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TITLE:
X.Org xserver File Locking Weakness and Security Issue

SECUNIA ADVISORY ID:
SA46460

VERIFY ADVISORY:
Secunia.com
http://secunia.com/advisories/46460/
Customer Area (Credentials Required)
https://ca.secunia.com/?page=viewadvisory&vuln_id=46460

RELEASE DATE:
2011-10-22

DISCUSS ADVISORY:
http://secunia.com/advisories/46460/#comments

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http://secunia.com/advisories/46460/

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https://ca.secunia.com/?page=viewadvisory&vuln_id=46460

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http://secunia.com/vulnerability_scanning/personal/
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DESCRIPTION:
A weakness and a security issue have been reported in X.Org xserver,
which can be exploited by malicious, local users to disclose system
and sensitive information and cause a DoS (Denial of Service).

1) The weakness is caused due to the "LockServer()" function
(os/utils.c) behaving differently when trying to create the lock file
and the lock file already exists as a symlink, depending on whether or
not the symlink points to an existing or non-existing file.

2) The security issue is caused due to a race condition within the
"LockServer()" function (os/utils.c) when setting the permissions of
the lock file, which can be exploited to change the permissions of
arbitrary files to mode 444 via symlink attacks.

SOLUTION:
Fixed in the GIT repository.

Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

PROVIDED AND/OR DISCOVERED BY:
The vendor credits vladz.

ORIGINAL ADVISORY:
http://lists.freedesktop.org/archives/xorg/2011-October/053680.html
http://cgit.freedesktop.org/xorg/xserver/commit/?id=6ba44b91e37622ef8c146d8f2ac92d708a18ed34
http://cgit.freedesktop.org/xorg/xserver/commit/?id=b67581cf825940fdf52bf2e0af4330e695d724a4

OTHER REFERENCES:
Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

DEEP LINKS:
Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

EXTENDED DESCRIPTION:
Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

EXTENDED SOLUTION:
Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

EXPLOIT:
Further details available in Customer Area:
http://secunia.com/vulnerability_intelligence/

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