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TITLE:
Cisco IOS GRE Decapsulation Vulnerability

SECUNIA ADVISORY ID:
SA21783

VERIFY ADVISORY:
http://secunia.com/advisories/21783/

CRITICAL:
Less critical

IMPACT:
Security Bypass

WHERE:
>From local network

OPERATING SYSTEM:
Cisco IOS R12.x
http://secunia.com/product/50/
Cisco IOS 12.x
http://secunia.com/product/182/

DESCRIPTION:
FX has reported a vulnerability in Cisco IOS, which can be exploited
by malicious people to bypass certain security restrictions.

The vulnerability is caused due to an error within the handling of
GRE packets with source routing information as the offset field is
not verified before being used to decapsulate a packet. This can
potentially be exploited to bypass access control lists on the router
by sending specially crafted packets.

The vulnerability affects Cisco IOS 12.0, 12.1, and 12.2 based trains
when configured with GRE IP or GRE IP multipoint tunnels.

NOTE: Cisco IOS version 12.0S, with a revision later than 12.0(23)S,
with CEF enabled is not affected.

SOLUTION:
Apply patch CSCuk27655, CSCea22552, or CSCei62762.

PROVIDED AND/OR DISCOVERED BY:
FX, Phenoelit.

ORIGINAL ADVISORY:
Phenoelit:
http://www.phenoelit.de/stuff/CiscoGRE.txt

Cisco:
http://www.cisco.com/warp/public/707/cisco-sr-20060906-gre.shtml

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About:
This Advisory was delivered by Secunia as a free service to help
everybody keeping their systems up to date against the latest
vulnerabilities.

Subscribe:
http://secunia.com/secunia_security_advisories/

Definitions: (Criticality, Where etc.)
http://secunia.com/about_secunia_advisories/


Please Note:
Secunia recommends that you verify all advisories you receive by
clicking the link.
Secunia NEVER sends attached files with advisories.
Secunia does not advise people to install third party patches, only
use those supplied by the vendor.

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