On Feb 27, 2007, at 3:33 AM, Steven M. Christey wrote:
Given the complex manipulations that can work in XSS attacks (see RSnake's
cheat sheet) as well as directory traversal, combined with the sheer
number of potential inputs in web applications, multipied by all the
variations in encodings, I wouldn't be surprised if they were effective in
finding those kinds of implementation bugs, even in well-designed
software.  Although successfully diagnosing some XSS without live
verification smells like a hard problem akin to the Ptacek/Newsham
"vantage point" issues in IDS.

With the track record of non-web fuzzers and PROTOS style test suites, why
do you think web app fuzzing is less likely to succeed?

It's not so much that I don't think fuzzing is useful, it's that I don't see "one size fits all" fuzzing _products_ being useful.

To me, it gets to an issue of informed vs. uninformed (or "white box" vs. "black box" if you prefer) testing. While they're both useful and should both be exercised, I believe (though I have no hard statistics to validate) that issues of coverage/state are always going to doom uninformed testing to being less effective than informed testing. For a fuzzer to be really meaningful, I believe that a "smart fuzzing" approach is going to be the best bet, and that makes it hard for a "one size fits all" product solution to be feasible.

To do smart fuzzing, a lot of setup time is necessary in establishing an appropriate test harness and cases that fully exercise the files, network interface data, user data, etc., that the software is expecting.

Perhaps I'm totally off base, and I invite any product folks here to chime in and correct my misconceptions.


Kenneth R. van Wyk
SC-L Moderator
KRvW Associates, LLC

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