Software Engineering Institute

ISAKMP (RFC 2408) defines a framework for authentication, key management, and the negotiation of Security Associations (SAs). The Internet Key Exchange protocol (IKE, RFC 2049) operates within the framework of ISAKMP and uses parts of Oakley (RFC 2412) and SKEME to negotiate and provide cryptographic key exchange for ISAKMP SAs. ISAKMP/IKE is commonly used by IPSec-based virtual private networks (VPNs).

The ISAKMP implementation used in the Check Point VPN server (VPN-1) and clients (SecuRemote, SecureClient) does not adequately validate Certificate Request payloads. As a result, a specially crafted ISAKMP packet could overflow a static memory buffer, writing arbitrary data on the stack.

An attacker who is able to send a UDP packet to the ISAKMP service (500/udp) could execute arbitrary code with the privileges of the VPN process, typically root or SYSTEM. No authentication is required to exploit this vulnerability.

Upgrade
This issue is resolved in Firewall-1/VPN-1 versions NG FP2 (released in April 2002) and 4.1 SP6 (June 2002). For further information, please see the Check Point ISAKMP Alert.

Check Point workarounds

The Check Point ISAKMP Alert provides the following advice for customers who are unable to upgrade:

Customers using affected releases, who are not able to upgrade at this time, can confirm that they are not affected by running "fw checklic encryption" for a false return.

Customers using affected releases, who have a VPN encryption license should disable the VPN encryption and confirm that there are no Objects with ISAKMP checked.

Customers who are running an earlier version of VPN-1/FireWall-1 4.1 SP5a and prior, and cannot upgrade should contact Check Point Technical Services for assistance.
Block or Restrict Access

Block or restrict access to the ISAKMP service (500/udp) from untrusted networks such as the Internet. This will disable IKE and ISAKMP functionality (authentication, key exchange, SA negotiation) which is likely to disable most VPN services. Depending on service requirements, it may be possible to operate VPN connections without IKE/ISAKMP by using static SAs and pre-shared keys. Note also that in most cases it is trivial for an attacker to spoof the source of a UDP packet.