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Re: Report OWASP WAF Naxsi bypass Vulnerability
From: Jeffrey Walton <noloader () gmail com>
Date: Tue, 26 Mar 2013 18:47:02 -0400

Tracked through issue 65
(http://code.google.com/p/naxsi/issues/detail?id=65), fixed at
check-in R545 (http://code.google.com/p/naxsi/source/detail?spec=svn545&r=545).

On Mon, Mar 25, 2013 at 10:00 PM,  <safe3q () gmail com> wrote:
OWASP WAF Naxsi bypass Vulnerability

Certain unspecified input is not properly handed in
naxsi_src/naxsi_utils.c naxsi_unescape_uri(u_char **dst, u_char **src,
size_t size, ngx_uint_t type) before being used to filtered. This can
be exploited to bypass some WAF rules.

Naxsi site
https://code.google.com/p/naxsi/

Affected
All the version

My site
http://safe3.com.cn/

My nick name is Safe3

It happens like that,the naxsi_unescape_uri function process the % url
decode,if the next char after the % is a hex char and not after the
hex char,then it will drop the % and the next char.So if we input a
sql keyword "s%elect",it will come to "slect" instead,this is not the
standard url decode way.Such as the IIS asp,it will process the
"s%elect" as a result of "select",so we can bypass some
WAF rules just like that.

I afford a standard url decode function patch as the follow to fix this issue:
...


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