Friday, April 3, 2009

Found a Security Flaw (The Need for Software Testing Everywhere)

Today I was paying a bill online, and I crashed the company’s IIS server (I promise, I did nothing wrong—intentionally). The good news: they write their code rather securely, so they are using parameterized queries rather than embedded SQL statements. The bad news (besides the crash itself) is that they were running with tracing enabled, so I saw the entire stack trace.

I called the company and got in touch with their tech guy. He was really polite on the phone and very open to feedback. I shared a bunch of info with him and thought I ought to document it. So here’s an Open Letter to All Admins Running IIS:

· You need to check your machine.config (and possibly web.config) files and make sure <trace enabled=”false” localOnly=”true” pageOutput=”false” requestLimit=”10” traceMode=”SortByTime”/> See for more info.

· Either spin up Microsoft Baseline Security Analyzer (MBSA) or use IISLockDown and URLScan to scan your server(s) security, especially in configuration. See

· You might also benefit from a security review/audit from an experienced, independent consultant.

Security Focus has a decent article on the issue: (it’s old but still accurate). NOTE there is a chance that running IISlockdown may break something. If your developers built the site with some dependency on what’s actually a security hole, locking down your server could cause issues. I highly recommend that you run this against a test deployment and then run all of your automated tests against that deployment, and that you do some manual testing.

You might also consider picking up copies of

  • “Improving Web Application Security” (MS Press),
  • “Building Secure Microsoft ASP.NET Applications (MS Press),
  • “Writing Secure Code” (I *highly* recommend this – it’s the bible on secure coding, especially in MS technologies), and
  • “Secure Development Lifecycle” (MS Press).

From more to less specific, these books are pointers on secure IIS configuration, ASP.NET coding, coding in general, and strategies for maintaining application security throughout lifecyles. The latter book is a great read if you’re on a larger team and/or need to influence management to give you the time for security-related work.

1 comment:

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