Software Engineering Institute

Internet Protocol version 6 (IPv6) is a IP standard that is designed to replace the Internet Protocol version 4 (IPv4). IPv6 Type 0 Routing headers can store multiple addresses and are processed by routers for generalized source routing.

Cisco IOS software contains a vulnerability that occurs when proccessing IPv6 Type 0 Routing headers. An attacker may be able to trigger this vulnerability by sending an IP packet with a speciallly crafted IPv6 Type 0 Routing header to a vulnerable system.

Cisco states that Type 2 Routing headers, commonly used in Mobile IPv6 implementations, cannot be used to trigger this vulnerability.

Note that a device with a configured IPv6 address accepting IPv6 packets that are tunneled over an IPv4 connection may also be vulnerable.

A remote unauthenticated attacker may be able to execute arbitrary code on an affected device, or create a denial of service condition.

Upgrade
See the Software Version and Fixes section of Cisco Security Advisory 20070124 for information on available upgrades.

Restrict Access

Restricitng public access to vulnerable systems or blocking IPv6 packets with Type 0 Routing headers by implementing management VLANs or Access Control Lists may mitigate this vulnerability. Note that networks not using mobile IPv6 can filter all packets that contain Routing headers.

Disable Services

Disabling IPv6 functionality on devices using IPv4 may prevent this vulnerability from being exploited.


For more information about these and other workarounds, see the workarounds section of Cisco Security Advisory 20070124 and Cisco PSIRT Document 81722.