Secunia

Some vulnerabilities have been reported in Cisco IOS, which can be exploited by malicious people to disclose sensitive information, manipulate certain data, or to cause a DoS (Denial of Service).

1) A memory leak exists in the handling of completed PPTP sessions, which can be exploited to exhaust memory on an affected system.

2) An error exists in the handling of PPTP sessions when virtual access interfaces are not removed from the interface descriptor block (IDB) and are not reused. This can result in an exhaustion of the interface descriptor block (IDB) limit.

Vulnerabilities #1 and #2 are reported in Cisco IOS versions prior to 12.3 with VPDN enabled.

3) Some errors exist in the Data-Link-Switching (DLSw) feature when processing UDP and IP protocol 91 packets. This can be exploited to cause a reload of the system or a memory leak.

4) An error exists in the processing of IPv6 packets, which can be exploited to prevent the interface from receiving additional traffic or to cause the device to crash (if RSVP service is configured on the interface) by sending a specially crafted IPv6 packet to the device.

Successful exploitation of this vulnerability requires that IPv6 and certain IPv4 UDP services are enabled.

5) An error exists in the implementation of Multicast Virtual Private Networks (MVPN), which can be exploited to create extra multicast states on the core routers via specially crafted Multicast Distribution Tree (MDT) Data Join messages. This can also be exploited to receive multicast traffic from VPNs that are not connected to the same Provider Edge (PE).

Successful exploitation of the multicast traffic leak requires that the attacker knows or guesses the Border Gateway Protocol (BGP) peering IP address of a remote PE router and the address of the multicast group that is used in other MPLS VPNs.

Solution
Update to the fixed version (please see the vendor's advisories for details).

Provided and/or discovered by
1, 2) The vendor credits Martin Kluge of Elxsi Security.
5) The vendor credits Thomas Morin.

Original Advisory
Cisco:
http://www.cisco.com/warp/public/707/cisco-sa-20080326-pptp.shtml
http://www.cisco.com/warp/public/707/cisco-sa-20080326-dlsw.shtml
http://www.cisco.com/warp/public/707/cisco-sa-20080326-IPv4IPv6.shtml
http://www.cisco.com/warp/public/707/cisco-sa-20080326-mvpn.shtml

Other references
Further details available in Customer Area

Deep Links
Links available in Customer Area