TITLE:
Windows XP Internet Connection Firewall Bypass Weakness

SECUNIA ADVISORY ID:
SA12793

VERIFY ADVISORY:
http://secunia.com/advisories/12793/

CRITICAL:
Less critical

IMPACT:
Security Bypass

WHERE:
Local system

OPERATING SYSTEM:
Microsoft Windows XP Professional
http://secunia.com/product/22/
Microsoft Windows XP Home Edition
http://secunia.com/product/16/

DESCRIPTION:
A weakness has been reported in Windows XP, which can be exploited to
bypass certain rules in the Internet Connection Firewall (ICF).

The problem is caused due to the firewall by default accepting
incoming connections to ports listened on by the "sessmgr.exe"
process.

This can e.g. be exploited by malicious, unprivileged users to host
an unauthorised service or by a trojan to accept incoming connections
by starting "sessmgr.exe" and then inject malicious code into the
running process.

Successful exploitation does not require administrative privileges on
an affected system.

The weakness has been reported in Windows XP SP2. Other versions may
also be affected.

NOTE: This is a general problem with personal firewalls and can be
exploited via any program granted access through the firewall without
user interaction. It is a known issue and have been discussed in the
security community about 2 years ago. PoC exploit code has also
priorly been released by Oliver Lavery.

SOLUTION:
Uncheck "Remote Assistance" under the "Exceptions" tab for the ICF
configuration.

Don't rely solely on personal firewalls to prevent unauthorised
Internet access.

PROVIDED AND/OR DISCOVERED BY:
Reported in ICF via "sessmgr.exe" by:
americanidiot[at]hushmail.com

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