For those of you who aren’t familiar with XSS Filter, a brief summary is that it is a client-side defense against reflected cross-site scripting (XSS) attacks.  It works by recognizing that reflected XSS attacks inject script into the string that the browser sends to the targeted web server.  If the server doesn’t neuter or strip out the injected script, it gets sent back to the browser and executed in the context of the target web page.  Bad things then happen.  At a high level, XSS Filter remembers the string that the browser sent to the server, and looks at the server’s response to see if any of the script was actually in that string.  If it was, then XSS Filter decides that it got there because it was injected by an XSS attack and blocks the script from executing.  The rest of the web page renders as usual.  This is a vastly oversimplified sketch of XSS Filter – for details, see the post by David Ross, inventor of XSS Filter on the Security Vulnerability Research and Defense blog.

So what does XSS Filter have to do with the SDL?  Well, for almost nine years, since XSS was first discovered at Microsoft, we’ve been trying to figure out effective ways to reduce vulnerability to XSS attacks.  Our focus has been on improving the ways that web page developers code their pages, and we’ve developed a lot of tools and techniques for making web content safer from XSS attacks and for detecting XSS vulnerabilities in live pages.  The SDL requires the use of many of these tools and techniques, and we’re sure we’ve prevented a lot of XSS vulnerabilities from being introduced into Microsoft web pages as a result. 

But while we identify (and the SDL requires) measures that allow developers to avoid classes of vulnerabilities, we also look to identify more sweeping solutions that can either 1) eliminate classes of vulnerabilities, 2) reduce their severity, or 3) reduce the likelihood of attacks being successful.  The process usually starts from deep understanding of a class of vulnerabilities and attacks, and then we broaden defenses from there.  In the case of XSS Filter, David’s years of work researching XSS led him to come up with an approach that blocks many of the most common vulnerabilities to reflected attacks found on the web today.  The solution is compatible with existing web pages (doesn’t “break the web”) and thus we were able to enable it by default for users of Internet Explorer 8.  Because it’s a client-side mitigation, it will help protect users from attacks even though the sites they visit may be vulnerable to XSS. 

Our work on buffer overrun defenses follows a somewhat similar pattern – we started by prescribing coding techniques, banning the use of some APIs, and building tools that detect coding constructs that look like buffer overruns.  As we gained a deeper understanding of how buffer overruns can be exploited, we enhanced the /GS compiler flag and added ASLR in a quest to cause classes of exploits to fail even if a buffer overrun remains.  We’re not yet close to eliminating the SDL requirements for use of tools and coding techniques, but the SDL also requires the use of the mitigations to reduce the severity of vulnerabilities that slip past.  Will we ever get to the point where the mitigating technologies are so strong that we can relax the coding requirements?  Maybe not, but we will continue to introduce technologies that reduce the chances of a successful attack.

Similarly, in the case of XSS, even after IE8 ships, the SDL will continue to require the use of safe web site coding practices and tools such as the Anti-XSS library both to protect users of browsers other than IE8 and to provide protection in recognition of the fact that XSS Filter is a mitigation or defense in depth rather than a complete solution.  But we’ll also be keeping our eyes open (and doing active research) in the quest for an even more effective defense – whether client or server side – that eliminates XSS for good.

This post is a little far afield from the normal content of the SDL blog, but I thought it was important to provide a picture of the role of security science and security research in defining SDL requirements and in making major improvements in software security.  You can read more about our work in security science in the Security Vulnerability Research and Defense blog.

For example, Reconnex that was recently absorbed by McAfee, touts "information protection" before compliance. Similarly, my friends from nexTier only mention "compliance" on a few pages. Even newly unveiled DLP resource  (DLP In-Depth portal) only contains a little bit  of information on how DLP solutions help with various compliance projects. People tout "data protection", " data security", "data governance" (aka "we know big words - bigger than you") or even "data risk management" (aka "we are confused about what we sell")

I decide to explore this curious phenomenon.

Initially, I thought that it was reverse compliance at work? People not wanting to know what content packs up and leaves their network. Then I thought that maybe DLP vendors just aren't "the bandwagon jumping kind" (yeah, right!) Then I thought that they are "beyond compliance" already :-)

But you know what? I actually think that it is something different, much more sinister. It is the ominous checklist mentality (here too)!  You know, DLP is newer than  most regulations (PCI DSS, HIPAA, FISMA, etc) and - what a shock! - the documentation for these mandates just doesn't mention DLP (or CMF) by name. Sure, they talk about data protection (e.g. PCI DSS Requirements 3 and 4), but mostly in terms of encryption, access control, logging (of course!).

Also, PCI DSS directly and explicitly says "get a firewall", "deploy log management", "get scanned", "install and update AV" - but where is DLP? Ain't there...

Yes, Virginia, folks who "go by the book" and just "do the minimum" are missing out on the chance to procure DLP while their compliance budgets are still flowing. To me that means that many still don't get the "compliance+" model - buy for compliance -> use for security, operations, having fun, etc. Think what a good DLP solution  will do for you in discovering regulated data across the entire organization, blocking those pesky email with SSNs, PHI (hi, HIPAA) and CCs (hi, PCI) as well as solving plenty of other problems ...