[UNIX] SuSE sdbsearch.cgi Security Weakness

From: support@securiteam.com
Date: 08/02/01 

From: support@securiteam.com
To: list@securiteam.com
Subject: [UNIX] SuSE sdbsearch.cgi Security Weakness
Message-Id: <20010802194209.954A713902@mail.der-keiler.de>
Date: Thu,  2 Aug 2001 21:42:09 +0200 (CEST)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com

  SuSE sdbsearch.cgi Security Weakness
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SUMMARY

The sdbsearch.cgi script is a part of SuSE distribution. A vulnerability
in this script allows attackers that are able to write local files (even
unprivileged local files) to get them executed with the privileges that
sdbsearch.cgi runs with.

DETAILS

Affected systems:
SuSE version 6.x
SuSE version 7.x (7.1 and 7.2 have tainting protection, but even with it
is still possible to pass sdbsearch files that should not be read)

Sdbsearch.cgi trusts the content of HTTP_REFERER variable, a variable that
is set by client during HTTP requests. Pieces of this data (the
HTTP_REFERER) are used later in the search engine (as keywords or
referring files).

A vulnerability in the script occurs if there is the possible of writing
local files on the target host (e.g. uploading through FTPd or any other
method). A vulnerability in the program allows attackers that access this
file to cause the sdbsearch to execute the arbitrary commands. This is
caused because sdbsearch will use the open() function to open up the
"keylist.txt" file which is known to be vulnerable to the standard pipe
open() based attack (only this time without the -T option).

Exploit:
Proof of concept is very simple; just create a harmful keylist.txt in /tmp
directory and send a request to HTTP that looks like this:

GET /cgi-bin/sdbsearch.cgi?stichwort=keyword HTTP/1.0
Referer: http://example.org/../../../../../tmp

/tmp/keylist.txt can include something of the sort of:
$ echo -e "keyword\0touch exploitable|" > /tmp/keylist.txt

After a successful attempt, there will be "exploitable" file in /tmp
directory.

Patch:
Filter the HTTP_REFERER variable.

ADDITIONAL INFORMATION

The information has been provided by <mailto:z33d@eth-security.net>
Maurycy Prodeus.

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