CVE-2005-4437 in Extended Interior Gateway Routing Protocol
Summary
by MITRE
MD5 Neighbor Authentication in Extended Interior Gateway Routing Protocol (EIGRP) 1.2, as implemented in Cisco IOS 11.3 and later, does not include the Message Authentication Code (MAC) in the checksum, which allows remote attackers to sniff message hashes and (1) replay EIGRP HELLO messages or (2) cause a denial of service by sending a large number of spoofed EIGRP neighbor announcements, which results in an ARP storm on the local network.
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Analysis
by VulDB Data Team • 06/13/2019
The vulnerability described in CVE-2005-4437 represents a critical weakness in the Extended Interior Gateway Routing Protocol implementation within Cisco IOS versions 11.3 and later. This flaw specifically affects the MD5 neighbor authentication mechanism that was designed to secure EIGRP communications between network devices. The vulnerability stems from an improper implementation where the Message Authentication Code is not properly integrated into the checksum calculation, creating a fundamental security gap that undermines the integrity of the authentication process. This weakness allows malicious actors to exploit the protocol's cryptographic implementation and compromise network security through various attack vectors.
The technical flaw manifests in the incorrect handling of message authentication codes within the EIGRP protocol's security framework. When EIGRP neighbor authentication is enabled using MD5, the system should compute a cryptographic hash that includes all relevant message components to ensure integrity and authenticity. However, the vulnerable implementation fails to include the MAC address information in the checksum calculation, which means that attackers can capture legitimate EIGRP messages and replay them without detection. This cryptographic weakness stems from a failure to properly validate the message integrity check, allowing for replay attacks that can bypass the authentication mechanism entirely. The vulnerability is particularly concerning because it affects the core security features of a widely deployed routing protocol, making it a prime target for network disruption attacks.
The operational impact of this vulnerability extends beyond simple authentication bypass to include significant network disruption capabilities. Attackers can leverage the weakness to perform two primary types of attacks: EIGRP HELLO message replay and spoofed neighbor announcement flooding. In the first scenario, malicious actors can capture legitimate EIGRP HELLO messages and replay them to maintain false neighbor relationships, potentially disrupting routing convergence and network stability. More severely, attackers can generate a large volume of spoofed EIGRP neighbor announcements that flood the local network segment, causing an ARP storm that consumes significant network resources and can lead to complete network disruption. This denial of service capability makes the vulnerability particularly dangerous in production environments where network stability is paramount.
The security implications of this vulnerability align with several established threat frameworks and standards, particularly those related to authentication failures and network protocol weaknesses. From a CWE perspective, this vulnerability maps to CWE-310, which addresses cryptographic weaknesses in authentication mechanisms, and CWE-264, which covers permissions, privileges, and access control issues. The attack patterns described in the vulnerability correspond to techniques outlined in the MITRE ATT&CK framework under the T1566 category for credential access and T1499 for network disruption. The vulnerability demonstrates how improper implementation of cryptographic functions can create security holes that are difficult to detect and exploit, making it a classic example of how subtle implementation flaws can have significant security consequences in network infrastructure protocols.
Organizations affected by this vulnerability should implement immediate mitigations to protect their network infrastructure. The primary recommended approach involves disabling EIGRP neighbor authentication if it is not essential for network security requirements, as the authentication mechanism itself is fundamentally flawed. Network administrators should also consider implementing additional security controls such as access control lists to limit EIGRP message sources and monitor for unusual EIGRP traffic patterns. Network segmentation and the use of network access control mechanisms can help limit the potential impact of successful attacks. Additionally, upgrading to Cisco IOS versions that contain the appropriate security patches is essential, as these updates address the specific cryptographic implementation flaws in the MD5 authentication mechanism. Regular network monitoring and intrusion detection system configurations should be enhanced to detect abnormal EIGRP traffic patterns that may indicate exploitation attempts. Organizations should also conduct thorough network assessments to identify all devices running vulnerable IOS versions and prioritize remediation efforts accordingly to prevent potential exploitation.