Apache byte range vulnerability script

["Gillman, Joel - SAINT CORPORATION" <gillmanj () SAINTCORPORATION COM>]

Hello --

I'd like to contribute a fix related to the Apache byte range
vulnerability detection script at
http://nmap.org/svn/scripts/http-vuln-cve2011-3192.nse .

The current script submits a range request of eleven individual
byte ranges, short and not overlapping, with the comment that eleven
is "one more than allowed".  This method may detect one of the early
vulnerability work-around configurations, but I don't believe it
reliably detects the (fixed) Apache versions 2.2.20 or 2.2.21 --
first, because I've found no mention of a limit of ten ranges in
connection with the Apache 2.2.20 or .21 releases, and second,
because a simple test against a running Apache 2.2.20 server did
not show that behavior.

Instead, I would suggest this change:
    "bytes=0-0,1-1,2-2,3-3,4-4,5-5,6-6,7-7,8-8,9-9,10-10"
becomes
    "bytes=0-,1-,2-"

This requests more content than is present at the original URL,
regardless of the length of that content, and so should trigger
consolidation of three ranges (with response code 206) into
one range of the entire URL contents (with response code 200).
Apache's (subtle) reference to this behavior is in section "Caveats"
of http://httpd.apache.org/security/CVE-2011-3192.txt .

I hope this contribution is useful.  :)

-- 
Joel Gillman
Security software developer
Saint Corporation            http://www.saintcorporation.com



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