IPsec VPN flaw could yield new round of attacks

Attackers could exploit a vulnerability in a security protocol widely used in VPNs to cause a denial of service or buffer overflows, or to launch malicious code.

Earlier this week, Finnish researchers announced a high-risk vulnerability in a security protocol that serves an important role in key exchanges in IPsec VPNs. The severity of the flaw depends on different vendors, some of whom report it exists in their products and others who for now maintain their offerings are unaffected. But its impact could be great, given those vendors include heavyweights Cisco Systems, 3Com, Juniper Networks,...

Microsoft and IBM.

At issue is the handling of an international standard known as Internet Security Association and Key Management Protocol (ISAKMP), published by the Internet Engineering Task Force to establish, negotiate, modify and delete security associations. ISAKMP is a derivative of IKE and provides a framework for transferring key and authentication data that's independent of authentication, encryption algorithm or any key-generation technique, according to an advisory issued by CERT-FI and the United Kingdom's National Infrastructure Security Coordination Center.

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The vulnerabilities discovered by researchers at the University of Oulu in Finland can cause a denial of service, format string problems and buffer overflows. In some instances, it also can be used by an attacker to execute code. But, its discoverers add, "ISAKMP/IKE client applications may be harder to attack than server applications because in some cases, it may be required that clients initialize the negotiation."

So far, the following vendors have this to report:

  • 3Com says it's investigating if any of its devices are impacted.
  • Cisco has released a security advisory addressing the vulnerabilities. That bulletin includes this warning: "When receiving certain malformed packets, vulnerable Cisco devices may reset, causing a temporary Denial of Service (DoS)."
  • Openswan says it's continuing to test its IPsec software that's widely used in Linux distributions such as Red Hat Linux, SuSE/Novell, Debian, Fedora Linux and Mandrake. It reports that openswan v-1 is safe but openswan v-2 is open to denial-of-service attacks. It urges users to upgrade to the just-released openswan-2.4.2, which fixes a 3DES flaw.
  • Entrust has issued a security bulletin.
  • IBM doesn't believe the flaw impacts its products running on the AIX operating system. Nonetheless, it recommends IPsec be configured to use IKE in the main mode.
  • Intoto says its iGateway VPN has been tested and found not to be vulnerable.
  • Juniper Networks' M/T/J/E-series routers and JUNOS Security/JUNOSe Security platforms are vulnerable. Changes have been made in the software's coding to fix the flaw.
  • Microsoft reports none of its products are affected.
  • Mitel Corp. says it isn't vulnerable but is watching its 6042 Managed VPN closely.
  • Secgo's Crypt IP gateway and client products may be impactedbecause of defects in a third-party toolkit Secgo uses. It advises users running Secgo Crypto IP Gateway or Client v3.2.26 or earlier to upgrade immediately.
  • Stonesoft Corp has issued its own advisory.
  • StrongSwan, which offers Linux-based IPsec software, said its products are not impacted.
  • TeamF1 Inc. reports it is not impacted.

Mitigation includes using packet filtering and accepting ISAKMP negotiations only from trusted IP addresses. Users also should avoid the "aggressive mode" in phase one of a key exchange. This reduces the number of exchanges and packets sent back and forth during a negotiation before there is a secure channel.

The same Finnish research outfit in 2002 warned of a major flaw in the popular Simple Network Management Protocol (SNMP). This latest discovery was found in conjunction with further research into SNMP. Japan's CERT also assisted, according to an advisory.

This was first published in December 2005

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