bugtraq - Re: Regular Expression Denial of Service

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Date: Fri, 11 Sep 2009 19:21:24 +0300
From: Gadi Evron <ge@...uxbox.org>
To: Alex Roichman <Alexr@...ckmarx.com>
Cc: bugtraq@...urityfocus.com, Ilja van Sprundel <ilja@...esec.org>
Subject: Re: Regular Expression Denial of Service

Alex Roichman wrote:
> Checkmarx Research Lab presents a new attack vector on Web applications. By
> exploiting the Regular Expression Denial of Service (ReDoS) vulnerability an
> attacker can make a Web application unavailable to its intended users. ReDoS
> is commonly known as a “bug” in systems, but Alex Roichman and Adar Weidman
> from Checkmarx show how serious it is and how using this technique, various
> applications can be “ReDoSed”. These include, among others, Server-side of
> Web applications and Client-side Browsers. The art of attacking the Web by
> ReDoS is by finding inputs which cannot be matched by Regexes and on these
> Regexes a Regex-based Web systems get stuck.
> 
> For further reading:
> http://www.checkmarx.com/NewsDetails.aspx?id=23&cat=3

Alex, nice work. Thank you for sharing it with us.

I'd recommend taking a look at Ilja van Sprundel's work with regular 
expression bugs in his Unusual bugs presentation.
... Where he played a bit with Google Code Search back in 2007, I think. 
He helped Google out by giving them his research, of course.

I found two versions online:
http://www.ruxcon.org.au/files/2006/unusual_bugs.pdf
http://www.slideshare.net/amiable_indian/unusual-bugs

Ilja and I later discussed creating a real regex fuzzer to discover 
vulnerabilities, but I at least never had the time to play with it. He 
might have, I am CC:ing him.

My best to Adar,

Gadi Evron,
http://www.gadievron.com/