Recent Facebook XSS Attacks Show Increasing Sophistication

Posted under Contributors, Facebook on April 21st, 2011 by

A few weeks ago, three separate cross-site scripting (XSS) vulnerabilities on Facebook sites were uncovered within a period of about 10 days. At least two of these holes were used to launch viral links or attacks on users – and it’s clear that attacks against Facebook users are becoming increasingly sophisticated.

The first issue came from a page on the mobile version of Facebook’s site. The interface was a prompt for posting stories to a user’s wall, and the parameter for the text of the prompt did not properly escape output. On March 28, a blogger identifying themselves as “Joy CrazyDaVinci” posted code that demonstrated how the vulnerability could be used to spread viral links:

<iframe id=”CrazyDaVinci” style=”display:none;”
src=”http://m.facebook.com/connect/prompt_feed.php?display=wap&user_message_prompt=’<script>window.onload=function(){document.forms[0].message.value=’Just visited http://y.ahoo.it/gajeBA Wow.. cool! nice page dude!!!‘;document.forms[0].submit();}</script>”></iframe>

This bit of HTML would be included in a viral page. The code sets the content of the wall post to a message that includes a link to a viral page, then submits the prompt automatically. Anyone clicking the link would get the same code executed on their account. The viral page could be used for malware distribution or phishing attacks, but in most cases where I saw this trick used, the page simply loaded advertisements or “offer spam”.

By the next day, several links were spreading virally and caught the attention of security researchers. Facebook moved quickly to patch the issue, and Crazy DaVinci issued an apology for the example code, explaining that versions of it had actually been circulating for several days prior and that the demonstration was intended to push Facebook for a fix.

On April 3, another XSS problem came to light, this time with a Facebook “channel” page used for session management. Both another security researcher and I had previously looked at this interface and found it properly escaped, so it’s likely a code update mistakenly changed the page’s behavior. Facebook again patched the problem soon after news of it spread.

I didn’t observe any viral exploitation of the second vulnerability in the wild, but after the first problem came to light, I noted that it was mostly used to submit a form already on the page for posting links. The payload made use of functionality within the vulnerable page, but XSS allows an attacker to do far more. I wondered when we might see a Facebook attack that made greater use of cross-site scripting’s potential.

What a Difference a Space Makes

I didn’t have to wait long. On April 7, I got word via Twitter of a Facebook app that had live XSS, but the app had disappeared before I got to see it in action. At first, I thought this was yet another case of XSS within the context of a Facebook app. But I soon found other version of the app which were still online, and I quickly realized this was actually an XSS problem with the Facebook Platform. Also, the XSS payload being used did much more than submit a form.

The attack used FBML-based Facebook apps, which render in the context of an apps.facebook.com page. Normally, Facebook filters code to prevent any scripts from directly modifying the page’s DOM, but the XSS problem gave attackers a bypass. When a user visited the app page, they would see what appeared to be a fairly benign page with a popular video.

Unlike many Facebook page scams, the promised video actually works – if you click play, the video will load and nothing unusual seems to happen. But as the code screenshot below reveals, that click does much more than load the video.

When the page first loads, the “video” is actually just an image placeholder with a link. Part of the href parameter for that link is shown above. Note the space after the opening quotation mark – that’s where the XSS comes in. Normally, Facebook would block a link to a javascript: URL. Adding the space worked around Facebook’s filters, but the browser would still execute the rest of parameter.

According to Facebook, it turned out that some older code was using PHP’s built-in parse_url function to determine allowable URLs. For example, while parse_url(“javascript:alert(1)”) yields a scheme of “javascript” and a path of “alert(1)”, adding whitespace gives a different result: parse_url(” javascript:alert(1)”) does not return a scheme and has a path of “javascript:alert(1)”. Other PHP developers should take note of the difference if parse_url is being used in security-related code.

A More Advanced Attack

Clicking the link executed an inline script that in turn added a script element to the page. This loaded more code from a remote address and included several parameters in the GET request. The parameters set variables within the remote code that specified what video to load, what URLs to use for viral posts, and so on. Multiple Facebook apps and domains were used for the viral links, but the main script always came from the same host. This helped the attack persist, since blocking one site would not stop it and the central code was loaded dynamically.

The remote code handled actually loading the video, but also included a number of functions which make use of having script access in a facebook.com context. The script would set the user as attending spam events, invite friends to those events, “like” a viral link, and even send IMs to friends using Facebook Chat.

When I came across the attack, one block of code had been commented out, but one blogger discovered a version of the attack a few days prior and saw it in action. This part loaded a fake login form which actually sent the entered username and password to a log interface on the attacker’s server. (Remember, this phishing form would appear in the context of a page with typical Facebook chrome.) Since the attack page would load even if a user was not logged in to Facebook, this could have also been a way to make sure a session was available before launching the other functions.

Fake videos and viral links are nothing new on Facebook, but most of these scams tend to be fairly simple. In fact, it’s not hard to find forums where people offer boilerplate code for launching such schemes – much like the first XSS worm above which simply submitted a form. But the April XSS attack involved multiple domains, multiple user accounts, and multiple methods for spreading and hijacking user accounts. And it still only scratched the surface of what’s possible with an XSS vulnerability. I expect we’ll see more XSS-based attacks and more powerful payloads in the future.

Postscript on Real-Time Research

I came across the April attack late one afternoon as I was preparing to leave work… so I could present on XSS at a local OWASP meeting! Those following me on Twitter saw a somewhat frantic stream of tweets as I tried to find live examples of the attack and sorted through the code while closely watching the clock and wrapping up last-minute presentation details. Earlier this week, I did some searching to review information for this post, and I came across this article from eWEEK: “Facebook Bully Video Actually an XSS Exploit“.

I was a bit surprised by it, as I hadn’t known about it before and saw that it quoted me. I then realized it was quoting my tweets! I then read that I had “confirmed to eWEEK on Twitter” one aspect of the story. At first I was confused, but then remembered that during my flood of tweeting, another user had sent an @ reply asking about the very detail the story talked about. Checking that tweet again, I found out the question had come from the article’s author.

I relate all this not because any of it bothered me, simply because (1) I found it somewhat fascinating that a few quick Twitter updates could become the primary source for a news article and (2) I was humbled to realize that a few quick Twitter updates could become the primary source for a news article! While it’s great that a story can spread so fast, it was certainly gave me a reminder to be careful when discussing topics of interest on a public forum. But I’m glad I can do my part in helping raise awareness of online dangers, particular the implications of XSS.

Looking at Facebook’s Strategy and Possible New Directions

Posted under Contributors, Facebook, General on November 15th, 2010 by

Over the last few months, Facebook has rolled out several significant new features, such as Places and the updated Groups. On Monday, Facebook is holding another event to announce what many expect to be an improved messaging feature. As I’ve watched these changes, I’ve been thinking about where Facebook might be headed.

At first, I started to think Facebook was simply looking to extend its reach by acting as an invisible layer of sorts. Anil Dash once talked about Facebook melting into the larger Web, but perhaps Facebook would end up becoming part of the underlying fabric of the Internet. In past public appearances, Facebook CEO Mark Zuckerberg seemed to be the kind of person who was content to remain in the background, and the company’s strategy seemed to reflect a similar style. I’ve mentioned before the idea of Facebook becoming and identity layer on the Internet, and innovations such as their Graph API have made it easier than ever for sites to integrate with Facebook.

But Facebook’s updated Groups feature changed my perspective, since it added functionality that would drive users back to facebook.com. Of course, the upgrade did enable e-mail as a way of interacting with groups. In some ways, Facebook’s overall strategy could be compared to Google’s. Years ago, many sites focused on “stickiness,” trying to keep users hooked. By contrast, Google drove users away by providing relevant links to other sites. But to see Google as non-sticky would be an oversimplification. In fact, the company built a successful ad network that extended its reach across the web. Also, Google has created a number of other products that many people stay logged into, such as Gmail.

And now, people are expecting Facebook to announce a web-based e-mail client that will compete with Gmail. I’m predicting that Facebook will roll out a new messaging system, but it won’t be a Gmail clone or simply another client for managing traditional POP/IMAP e-mail. That’s not to say there won’t be any e-mail gateway, but I think Facebook’s plans will go much further. I’m guessing that at least part of the new system will involve somehow extending private messaging features across Facebook-integrated websites.

In any event, I think Facebook’s announcement will include at least a few surprises for those who have been discussing the possibilities. Facebook has a history of introducing features that aren’t quite what people expected – and often end up leading to practical implementations of ideas that were previously niche experiments. Personally, I think it’s a bit short-sighted to think that Facebook would simply join the market for web-based e-mail without trying to reinvent it, especially given the service’s cautiousness about past features that allowed or potentially allowed spam-like behaviors.

Facebook has also been accused many times of somehow standing in opposition to “openness.” Personally, I think the term has become a buzzword that’s often used without much specificity. And even though I’ve often been a critic of Facebook, I do think many of the accusations aren’t entirely fair. From RSS feeds to developer APIs, Facebook has opened up data in ways that many other sites can’t claim. Today’s Facebook is certainly far more “open” that years ago – in fact, I would argue that the site has at times been too open lately, such as when some user data became reclassified as “publicly available” last fall. But regardless of Facebook’s degree of openness, the company has always been careful to maintain a high degree of control over information and features on the site. This can be positive, such as quickly removing malware links, or negative, such as controversial decisions to bar users or certain content.

Either way, that control has helped the site build a powerful database of profiles that generally reflects real people and real relationships. That’s part of what fascinated me about the site’s recent spat with Google over contact information. In the past, a list of e-mail addresses was about the only semi-reliable way to identify a group of people across the Internet. Now, many sites rely on Facebook’s social graph for that function. In terms of identity, the value of e-mail addresses has declined, and I don’t think exporting them from Facebook would provide as much value as Google might think. On the other hand, Google may realize this and be so concerned about the shift that they’re trying to curb Facebook’s influence. This would especially make sense if Google intends to introduce a more comprehensive social networking product that would need e-mail addresses as a starting point. Regardless, I’m sure Google feels threatened by the prospect of Facebook providing a better alternative to traditional e-mail – a change that would only bolster the value of a Facebook profile as the primary way to identify a typical Internet user.

Thoughts on the Wall Street Journal’s Facebook Investigation

Posted under Contributors, Facebook on October 25th, 2010 by

A front-page story in last Monday’s Wall Street Journal declared a “privacy breach” of Facebook information based on an investigation conducted by the paper. The Journal found that third-party applications using the Facebook Platform were leaking users’ Facebook IDs to other companies, such as advertising networks.

The report generated controversy across the Web, and some reactions were strongly negative. On TechCrunch, Michael Arrington dismissed the article as alarmist and overblown. Forbes’ Kashmir Hill surveyed other responses, including a conversation on Twitter between Jeff Jarvis and Henry Blodget, and expressed skepticism over the Journal’s tone.

I’ve been a bit surprised by the degree to which some have written off the Journal’s coverage. Some may disagree with the label of “privacy breach,” but I thought the report laid out the issues well and did not paint the problem as a conspiracy on the part of Facebook or application developers. Either way, I’m glad to see that the article has sparked renewed conversation about shortcomings of web applications and databases of information about web users. Also, many may not realize that information leakage on the Facebook Platform has historically been even worse.

Information leakage via a referrer is not a new problem and can certainly affect other websites. But that doesn’t lessen the significance of the behavior observed in the WSJ investigation. Privacy policies are nearly always careful to note that a service does not transfer personally identifiable information to third parties without consent. Online advertising networks often stress the anonymity of their tracking and data collection. The behavior of Facebook applications, even if unintentional, violated the spirit of such statements and the letter of Facebook’s own policies.

Some people downplayed the repercussions of such a scenario on the basis that it did not lead to any “private” profile information being transferred to advertisers – a point Facebook was quick to stress. Yet when did that become the bar for our concept of acceptable online privacy? Should other services stop worrying about anonymizing data or identifying users, since now we should only be concerned about “private” content instead of personally identifiable information? Furthermore, keep in mind that Facebook gets to define what’s considered private information in this situation – and that definition has changed over the last few years. At one time in the not-too-distant past, even a user’s name and picture could be classified as private.

Many reactions have noted that a Facebook user’s name and picture are already considered public information, easily accessed via Facebook’s APIs. Or as a Facebook spokesmen put it, “I don’t see from a logic standpoint how information available to anyone in the world with an Internet connection can even be ‘breached.’” But this argument fails to address the real problem with leaked IDs in the referrer. The issue was not simply what data applications were leaking, but when and how that data was leaked. The problem was not that advertisers could theoretically figure out your name given an ID number – it’s that they were given a specific ID number at the moment a user accessed a particular page. Essentially, advertisers and tracking networks were able to act as if they were part of Facebook’s instant personalization program. Ads could have theoretically greeted users by name – the provider could connect a specific visit with a specific person.

Interestingly enough, many past advertisements in Facebook applications did greet users by name. Some ads also including names and pictures of friends. Facebook took steps several times to quell controversies that arose from such tactics, but I’m not sure many people understood the technical details that enabled such ads. Rather than simply leak a user’s ID, applications were actually passing a value called the session secret to scripts for third-party ad networks.

With a session secret, such networks could (and often did) make requests to the Facebook API for private profile information of both the user and their friends, or even private content, such as photos. Typically, this information was processed client-side and used to dynamically generate advertisements. But no technical limitations prevented ad networks from modifying their code to retrieve the information. In fact, a number of advertisements did send back certain details, such as age or gender.

Change to the Facebook Platform, such as the introduction of OAuth earlier this year, have led to the deprecation of session secrets and removed this particular problem. I’m not sure how much this sort of information leakage or similar security problems motivated the changes, but problems with session secrets certainly persisted quite a while prior to them. If the WSJ had conducted their study a year ago, the results could have been even more worrying.

Still, I’m glad that the Journal’s research has led many to look more closely at the issues they raised. First, the story has drawn attention to more general problems with web applications. Remember, the Web was originally designed for accessing static pages of primarily textual information, not the sort of complex programs found in browsers today. (HTML 2.0 didn’t even have a script tag.) Data leaking via referrers or a page’s scripts all having the same scope are problems that go beyond Facebook apps and will likely lead to more difficulties in the future if not addressed.

Second, people are now investigating silos of information collected about website visitors, such as RapLeaf’s extensive database. Several responses to the Journal piece noted that many such collections of data provide far more detail on web users and are worthy of greater attention. I agree that they deserve scrutiny, and now reporters at the Journal seem to be helping in that regard as well.

We’ve entered an age where we can do things never previously possible. Such opportunities can be exciting and clearly positive, but others could bring unintended consequences. I think the availability and depth of information about people now being gathered and analyzed falls into the latter category. Perhaps we will soon live in a world where hardly any bit of data is truly private, or perhaps we will reach a more open world through increased sharing of content. But I think it well worth our time to stop and think about the ramifications of technological developments before we simply forge ahead with them.

Over the last few years, I’ve tried to bring attention to some of the issues relating to the information Facebook collects and uses. They’re certainly not the only privacy issues relevant to today’s Internet users, and they may not be the most important. But I think they do matter, and as Facebook grows, their importance may increase. Similarly, I think it wrong to dismiss the Journal’s investigation as “complete rubbish,” and I look forward to the rest of the dialogue they’ve now generated.

Instant Personalization Program Gets New Partner, Security Issue

Posted under Contributors, Facebook, General on September 21st, 2010 by

Facebook announced last week that movie information site Rotten Tomatoes would join Docs.com, Pandora, and Yelp as a partner in the social networking service’s “instant personalization” program. Rotten Tomatoes will now be able to automatically identify and access public information for visitors logged in to Facebook, unless those users have opted out of the program. This marks the first new partner since Facebook launched the feature earlier this year.

Soon after that initial roll-out, security researchers noted vulnerabilities on Yelp’s website that allowed an attacker to craft pages which would hijack Yelp’s credentials and gain the same level of access to user data. TechCrunch writer Jason Kincaid reported on the cross-site scripting (XSS) holes, and made this prediction: “I suspect we’ll see similar exploits on Facebook partner sites in the future.”

Kincaid’s suspicions have now been confirmed, as the latest site with instant personalization also had an exploitable XSS vulnerability, which has now been patched. I’ll quickly add that Flixster, the company behind Rotten Tomatoes, has always been very responsive when I’ve contacted them about security issues. They have assured me that they have done XSS testing and prevention, which is more than could be said for many web developers. In posting about this issue, I primarily want to illustrate a larger point about web security.

When I heard about the expansion of instant personalization, I took a look at Rotten Tomatoes to see if any XSS problems might arise. I found one report of an old hole, but it appeared to be patched. After browsing around for a bit, though, I discovered a way I could insert some text into certain pages. At first it appeared that the site properly escaped any characters which could lead to an exploit. But ironically enough, certain unfiltered characters affected a third-party script used by the site in such a way that one could then execute arbitrary scripts. Since I had not seen this hole documented anywhere, I reported it to Rotten Tomatoes, and they promptly worked to fix it.

I’ve long argued that as more sites integrate with Facebook in more ways, we’ll see this type of problem become more common. Vulnerable applications built on the Facebook Platform provided new avenues for accessing and hijacking user accounts; now external websites that connect to Facebook open more possible security issues. As Kincaid noted in May, “Given how common XSS vulnerabilities are, if Facebook expands the program we can likely expect similar exploits. It’s also worth pointing out that some large sites with many Facebook Connect users – like Farmville.com or CNN – could also be susceptible to similar security problems. In short, the system just isn’t very secure.”

Overcoming such weaknesses is not a trivial matter, though, especially given the current architecture of how scripts are handled in a web page. Currently, any included script has essentially the same level of access and control as any other script on the page, including malicious code injected via an XSS vulnerability. If a site uses instant personalization, injected scripts can access the data used by Facebook’s code to enable social features. That’s not Facebook’s fault, and it would be difficult to avoid in any single sign-on infrastructure.

Of course, all of this applies to scripts intentionally included in the page as well, such as ad networks. With the Rotten Tomatoes roll-out, Facebook made clear that “User data is never transferred to ad networks.” Also, “Partner sites follow clear product/security/privacy guidelines,” and I assume Facebook is monitoring their usage. I’m not disputing any of these claims – Facebook is quite correct that advertisers are not getting user data.

But that’s due to policy limitations, not technical restrictions. Rotten Tomatoes includes a number of scripts from external sources for displaying ads or providing various functions. Any of these scripts could theoretically access a Facebook user’s information, though it would almost certainly be removed in short order. I did find it interesting that an external link-sharing widget on the site builds an array of links on the page, including the link to a user’s Facebook profile. This happens client-side, though, and the data is never actually transferred to another server.

I bring up these aspects simply to note the technical challenges involved in this sort of federated system. I think it’s very possible that we will eventually see ad network code on a Facebook-integrated site that tries to load available user data. After all, I’ve observed that behavior in many Facebook applications over the last few years – even after Facebook issued explicit policies against such hijacking.

These dangers are part of the reason why JavaScript guru Douglas Crockford has declared security to be the number one problem with the World Wide Web today. Crockford has even advocated that we halt HTML5 development and focus on improving security in the browser first. While that won’t likely happen, I think Crockford’s concerns are justified and that many web developers have yet to realize how dangerous cross-site scripting can be. Perhaps these issues with instant personalization sites will help increase awareness and understanding of the threat.

Postscript: This morning, an XSS vulnerability on Twitter led to script-based worms (somewhat reminiscent of “samy is my hero”) and general havoc across the site. This particular incident was not related to any mashups, but once again emphasizes the real-world security ramifications of cross-site scripting in a world of mainstream web applications.

Update (Sep. 27): Today news broke that Scribd had also become part of Facebook’s Instant Personalization program. I took a look at the site and discovered within minutes that it has a quite trivial XSS vulnerability. This particular issue should have been obvious given even a basic understanding of application security. It also indicates that Facebook is not doing much to evaluate the security of new instant personalization partners. Update 2: Scribd patched the most obvious XSS issue right about the time I updated this post: entering HTML into the search box brought up a page that loaded it unfiltered. Another search issue remained, however: starting with a closing script tag would still affect code later in the results page. After about half an hour, that problem was also patched. I’m glad Scribd moved so quickly to fix these problems, but I still find it disconcerting they were there to start with. I’ve not done any further checking for other XSS issues.

Facebook Places Brings Simple Location Sharing to the Masses

Posted under Contributors, Facebook on August 19th, 2010 by

Yesterday, Facebook announced a much-anticipated feature that allows users to easily post their current location on the site. The new setup, known as Facebook Places, works much like other location-based services, such as Foursquare or Gowalla, by letting users “check in” at nearby places. Geolocation providers, such as a mobile phone’s GPS, pinpoint the user, and Localeze provides the initial database of places. Eventually, users will be able to add their own locations to the Facebook map. Inside Facebook has a run-down of the overall functionality.

Facebook also allows your friends to check you in at locations, and these check-ins are indistinguishable from ones you made for yourself. In typical opt-out fashion, you can disable these check-ins via your privacy settings, and you’ll be asked about allowing them the first time a friend checks you in somewhere.

Even if you stop friends from checking you in to places, however, they can still tag you with their check-ins, similar to how friends can tag you in photos or status updates. Such tags will appear on your wall, as tagged status updates do now. You’ll be able to remove tags after the fact, but it doesn’t seem that you’ll be able to prevent friends from tagging you altogether.

Applications have two new permissions related to places. One gives access to your check-ins, the other gives access to your friends’ check-ins as well. Both will appear in the list of requested permissions when you authorize an application, and they are required for API access to check-ins. If your friends grant an application access to friends’ check-ins, you can prevent yours from appearing via “Applications and Websites” privacy controls.

API access is currently read-only – authorized applications can access your check-ins, but can’t submit check-ins to Facebook. That sort of functionality is currently in closed testing, though.

ReadWriteWeb has a nice guide to applicable privacy settings. When these controls first appeared on my profile, Facebook set the visibility for all my check-ins to “Friends Only” by default and disabled API access to my check-ins via friends by default. But they also enabled by default another setting which makes individual check-ins visible to anyone nearby at the time, whether friends or not. The option for letting friends check me in was not specifically set, but apparently I would have been prompted the first time a friend checked me in.

According to Facebook, you will only be able to check-in at locations near where you are, as determined by the geolocation feature of your browser (or your phone’s GPS for the iPhone app). I’m a bit suspicious on how difficult faking a check-in will be, but I don’t yet have the ability to test that out.

Facebook’s initial geolocation rollout brings a fairly modest feature set, but when integrated with Facebook Pages and made available to a network of 500 million people, the service offers great potential. As with other recent changes, adding check-ins reduces friction for users to share their location and provides Facebook with another valuable set of data about people’s daily activities. It remains to be seen whether users will react with discomfort over the potential for an entirely new meaning of “Facebook stalking” or with excitement over potential new product offerings. Either way, the amount and variety of information under Facebook’s control continues to expand rapidly.

Security Through Obscurity and Privacy in Practice

Posted under Contributors, General on July 27th, 2010 by

Yesterday, security researcher Ron Bowes published a 2.8GB database of information collected from public Facebook pages. These pages list all users whose privacy settings enable a public search listing for their profile. Bowes wrote a program to scan through the listings and save the first name, last name, and profile URI of each user (though only if their last name began with a Latin character). The database includes this data for about 171 million profiles.

On the one hand, I wasn’t entirely surprised by this news – it was only a matter of time before someone started building up such a dataset. I’ve previously mentioned that developer Pete Warden had planned on releasing public profile information for 210 million Facebook users until the company’s legal team stepped in. But nothing technical prevented someone else from attempting the task and posting data without notice. I imagine Facebook may not be too happy with Bowes’ data, but I’m not going to delve into the legal issues surrounding page scraping.

However, the event did remind me of a related issue I’ve pondered over the last few months: the notion of “security through obscurity” as it relates to privacy issues.

I’ve often referenced the work of danah boyd, a social media researcher that I highly respect. In a talk earlier this year at WWW2010 entitled, ”Privacy and Publicity in the Context of Big Data,” she outlines several excellent considerations on handling massive collections of data about people. One in particular that’s worth remembering in the context of public Facebook information: “Just because data is accessible doesn’t mean that using it is ethical.” Michael Zimmer at the University of Wisconsin-Milwaukee has made similar arguments, noting that mass harvesting of Facebook data goes against the expectations of users who maintain a public profile for discovery by friends, among other issues. Knowing some of the historical issues with academic research involving human subjects, I tend to agree with these positions.

But a related point from boyd’s talk concerns me from a security perspective: “Security Through Obscurity Is a Reasonable Strategy.” As an example, she notes that people talking in public settings may still discuss personal matters, but they rely on being one conversation among hundreds to maintain privacy. If people knew other people were specifically listening to their conversation, they would adjust the topic accordingly.

In this “offline” example, taking advantage of obscurity makes sense. But boyd applies the same idea online: “You may think that they shouldn’t rely on being obscure, but asking everyone to be paranoid about everyone else in the world is a very very very unhealthy thing…. You may be able to stare at everyone who walks by but you don’t. And in doing so, you allow people to maintain obscurity. What makes the Internet so different? Why is it OK to demand the social right to stare at everyone just because you can?”

I would respond that at least three aspects make the Internet different. First, you rarely have anyway of knowing if someone is “staring at you” online. Public content on Facebook gets transferred to search engines, application developers, and individual web surfers every day without any notification to the creators of that content. Proxies and anonymizers can spoof or remove information that might otherwise help identify the source of a request. And as computing power increases each day, tracking down publicly accessible resources becomes ever easier.

Second, the nature of online data means that recording, parsing, and redistributing it tends to be far simpler than in the offline world. If I want to record someone’s in-person conversations, it’s theoretically possible that I could acquire a small recording device, place it in a convenient location, save the audio from it, type up a transcript of the person’s words, then send it to another person to read. But if I want to record someone’s conversations on Twitter (as an example), I can have all them in a format understandable to various computer-based analysis tools in just a few clicks. In fact, I could setup an automated system which monitors the person’s Twitter account and updates me whenever certain words of interest appear. Add the fact that this is true of any public Twitter account, and the capabilities for online monitoring grow enormously.

Finally, while digital content is in some ways more ephemeral than other media, web data tends to persist well beyond a creator’s ability to control. Search engine caches, archival sites, and user redistribution all contribute to keeping content alive. If someone records a spoken conversation on a tape, the tape can be destroyed before copies are made. But if you (or a friend of yours) post a sentence or photo on a social networking site, you may never be able to erase it fully from the Internet. Several celebrities have learned this the hard way lately.

From a privacy perspective, I wholeheartedly agree with boyd that we can’t expect users to become paranoid sysadmins. The final point of my own guide to Facebook privacy admonished, “You Have to Live Your Life.” But from a security perspective, I know that there will always be people and automated systems which are “staring at you” on the Internet. I’ve seen time and again that if data is placed where others can access it online, someone will access it – perhaps even unintentionally (Google indexes many pages that were obviously not meant for public consumption).

In my opinion, the only way to offer any setup online which resembles the sort of “private in public” context boyd described requires some sort of a walled garden, such as limiting your Facebook profile to logged in users. That alone still doesn’t provide the same degree of privacy, since many fake profiles exist and applications may still have access to your data. But while “security through obscurity” (or perhaps more accurately, privacy through obscurity) may be a decent strategy in many “offline” social situations, it simply can’t be relied on to protect users and data online.

Facebook users are starting to discover this firsthand. I’ve seen several reactions to Bowes’ release that characterize it as a security issue or privacy issue, and people have seemed quite surprised that building such a dataset was even possible. Yet it really shouldn’t come as a surprise to someone familiar with current technology and ways of accessing Facebook data. And it won’t be the last time we see someone make use of “public” data in surprising ways. Some of these uses may be unfortunate or unethical (see above), but we’ve often seen technology steam ahead in pursuit of fortune, and the web has many users with differing ideas on ethics. Reversing the effects of such actions may prove impossible, which is why I would argue we need to prevent them by not trusting obscurity for protection. And how do we balance this perspective to avoid unhealthy paranoia? I’m honestly not sure – but if content is publicly accessible online without any technical limitations, we can hardly consider it immune to publicizing.

Spam via Facebook Events Highlights Ongoing Challenges

Posted under Contributors, Facebook on July 26th, 2010 by

Earlier today, I received an invitation to a Facebook event from “Giovanna” – someone I’d never heard of and certainly never added as a friend. The invite came as a bit of a surprise, since my profile was fairly locked down. While anyone could search for it, all profile information was set to “Friends Only,” and sending messages or making friend requests was limited to “Friends of Friends.” None of my friends seem to know Giovanna, and her profile is probably fake anyway.

The event title proclaimed “iPhone Testers Needed!” and might be enticing to users who want an iPhone. While the event page included more information on the supposed testing program, the invite was followed by a message from the event creator. Once you’re on the guest list for a Facebook event, the event administrators can send out Facebook messages you’ll receive, regardless of privacy settings. This particular message (which also arrived in my e-mail inbox due to notifications settings) included a link to the iPhone opportunity, which unsurprisingly was a typical “offer” page that required me to submit personal information and try out some service before I could get my fancy new phone.

I began investigating how this all happened. When you create a Facebook event and try to invite people, you’ll only see a list of your friends to choose from. But it turns out that on the backend, nothing prevents you from submitting requests directly to Facebook with other people’s Facebook IDs. In my testing, I’ve been able to send event invitations to other users even if we’re not friends and they have tight privacy settings. I’m guessing that using this technique to invite more than a few people could raise a spam alert, but I’m not sure. Also, an event invitation does not give the event creator increased access to any profile information of guests, but as already noted, it does let event administrators send messages to people they might otherwise not be able to contact.

I’m sure Facebook will take action soon to clamp down on this particular loophole, so I think it unlikely we’ll see it exploited too widely. (The iPhone testing event currently has around 1800 guests – significant, but tiny compared to other Facebook scams.) But it does demonstrate the sort of challenges Facebook is having to handle as their network and power expand. Several years ago, when the site was used for little besides keeping in touch with college classmates and other offline friends, Facebook was seen as mostly spam-free, in contrast to services like Myspace. Now that applications, social gaming friends, and corporate brands have all become integral parts of the Facebook experience, black hat marketers keep finding new ways to spread links among users. And worse, those tricks can often be used to spread malware as well.

I do think that Facebook wants to avoid annoying users with spam, and works to prevent your inbox on the site from becoming as flooded as a typical e-mail account. But a network of 500 million people presents a very enticing target, and we’ll keep seeing new scam ideas pop up as Facebook expands and adds features. In the mean time, continue to be wary of any links  promising a glamorous reward for free.

Secure Your WordPress By Learning From My Mistakes

Posted under Contributors, General on June 25th, 2010 by

Several weeks ago, I managed to create a small ruckus on Twitter by issuing a warning about a possible WordPress vulnerability. I was rather embarrassed to eventually discover that the actual problem related to a backdoor still on my server from a previous hack. This was not my first lesson in WordPress security, but it was certainly a memorable one.

I first created this blog in 2007 after finding basic CSRF issues in the first publicly available OpenSocial application. At the time, I admittedly knew very little about application security (not that I know much now!), but I was interested in many aspects of building online social networking systems, and that led me to research security issues more and more. Over time, this blog grew and several other projects hosted on the same server fell by the wayside. As my understanding of security also grew, I found some of my sites hacked a few times, and I undertook a number of steps to secure this WordPress installation.

That maintenance contributed to the confidence I had in my warning on Twitter – malicious scripts kept popping up in my site’s footer, and the only apparent problem were some suspicious requests to a particular WordPress interface. I had looked gone through all my plug-ins (the apparent source of previous attacks), double-checked my permissions, changed passwords, etc. I finally did a thorough sweep of every single folder on my site, and lurking in an upload folder, I found a sophisticated PHP backdoor.

I’m guessing that file originally been placed during a much older attack and I’d simply missed it until now. Since deleting it and taking even more steps to protect my blog, I’ve not had any more trouble. I wouldn’t presume to think this site is 100% secure and I’ve never claimed to be an expert on application security, much less WordPress or PHP security, but I’m now quite confident that I’ve taken enough precautions to avoid most attacks.

That leads me to the following list of steps I’ve performed to harden this particular WordPress site. If you’ve not taken the time to ensure your blog is secure, this may be a good guide for you to start with. I’m indebted to many websites on WordPress security, and while I would want to link to all of them, I’m honestly not sure of all the specific ones I’ve drawn from and it would take a while to piece them together. A quick search will bring up many helpful recommendations, and I encourage you to check them out in addition to these tips.

  • Stay updated. Running the most current version of WordPress is probably the most important step. My host offers automatic updating for my installations. Also, be sure to keep your plug-ins updated as well.
  • Protect other sites. If you have more than one website running on the same server, make sure all of them are secure. One vulnerable application can compromise others. If you have sites that you don’t maintain, consider deleting them or locking them down to avoid future problems.
  • Scan through all of your folders. If you haven’t done this in a while, now would be a good time. Look through what files are present and keep an eye out for anything suspicious. Check your WordPress files against a fresh download to make sure they line up.
  • Scan through all of your permissions. This should be fairly easy with an FTP program that displays permissions settings. With rare exception, I keep files at chmod 644 and folders at chmod 755.
  • Periodically change passwords. Definitely modify your passwords if you’ve recovered from an attack. Remember to change your database password (and corresponding line in wp-config.php) as well as account passwords.
  • Use modified passphrases. This is one tip I don’t see often, but it’s one of my favorite tricks. Rather than simply jumbling characters into a password you have trouble remembering, start with a sentence. Not something terribly common, but something familiar to you. Pick one with at least six words in it. Take the whole sentence, with capitalization and punctuation, and add some complexity – append some numbers and punctuation at the beginning or end, and maybe change a few letters to numbers (such as “3″ for “e”). You should then have a very strong “password” that’s much easier to remember. Many websites and applications will let you use spaces and hundreds of characters in your password. But once again: avoid common phrases, include at least six words, and don’t just use a sentence without adding some numbers and special characters.
  • Check your users table in the database. I’ve seen attacks before that lead to the creation of an administrative account which is then hidden from the list of users in the web-based control panel. I’ve never quite understood why hidden users should be allowed, but that could be part of the attack to begin with. Anyway, just to be careful, I like to look at the actual table in the database and see if any other accounts have administrative privileges.
  • Double-check and clean up all plug-ins. I’ve deleted every plug-in I don’t use, and I try to keep all of my active plug-ins current. If you have a plug-in that’s no longer maintained or hasn’t been updated in a long time, you should probably check and see if a newer replacement is available. In my experience, plug-ins can be one of the weakest points in your WordPress installation. It’s kind of like a certain other site I know well – Facebook itself tends to be pretty secure, but you can often access data through vulnerable Facebook applications.
  • Add HTTP authentication to your wp-admin folder. This is covered in many places online so I’ll not recap specific steps here. And I’ll add that I realize this is not a silver bullet – basic authentication sends passwords in cleartext (so don’t use the same credentials as your WordPress account), and the traffic is not encrypted if you’re not using SSL/TLS. But adding another login prompt for the admin panel adds friction and may repel less-determined attackers. (This tip is obviously geared towards those who don’t have user accounts for non-admins.)
  • Move wp-config.php to a folder not as easily accessible. You can place wp-config.php one folder above your WordPress install; under my hosting setup, this location does not correspond to any public website folder. I also set mine to chmod 644 after changing it.
  • Rename your admin account. Several means exist to do this; I simply edited the record in the database.
  • Change your table prefix. This can be a bit of a hassle, but plug-ins exist (see below) to help. I’ll admit that I still need to check this one off my own list; long story.
  • Disable interfaces such as XML-RPC if you don’t use them. I don’t doubt that the programmers behind WordPress have worked hard to secure these interfaces, but I simply don’t like having another avenue of accessing administrative functions. And I think it’s not a bad idea to disable features you don’t actually need.
  • Use security tools. I installed the WP Security Scan plug-in after reading about it on WordPress’ own hardening guide.
  • Keep monitoring your site. I make a habit of loading up my homepage ever so often, hitting “View Source,” and scanning through the HTML. If I ever see an unfamiliar script or iframe element, I look closer.

That’s my personal list of WordPress security tips, based on many helpful resources and my own experiences of getting hacked. These certainly don’t apply to everyone, more could be added, and your mileage may vary, but hopefully this will help others avoid some of the problems I encountered. Be sure to look at other people’s advice as well and watch out for any WordPress security news.

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