CVE-2005-4436 in IOS
Summary
by MITRE
Extended Interior Gateway Routing Protocol (EIGRP) 1.2, as implemented in Cisco IOS after 12.3(2), 12.3(3)B, and 12.3(2)T and other products, allows remote attackers to cause a denial of service by sending a "spoofed neighbor announcement" with (1) mismatched k values or (2) "goodbye message" Type-Length-Value (TLV).
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Analysis
by VulDB Data Team • 08/02/2017
The vulnerability described in CVE-2005-4436 represents a critical denial of service weakness within the Extended Interior Gateway Routing Protocol implementation in Cisco IOS software. This flaw specifically affects EIGRP versions 1.2 and later, which were introduced in Cisco IOS releases 12.3(2), 12.3(3)B, 12.3(2)T, and subsequent versions. The vulnerability stems from insufficient validation mechanisms within the routing protocol's neighbor discovery and maintenance processes, creating an exploitable condition that can be leveraged by remote attackers to disrupt network operations.
The technical exploitation of this vulnerability occurs through the transmission of specially crafted spoofed neighbor announcements that manipulate either the k values or employ goodbye message Type-Length-Value (TLV) structures. These k values represent key parameters used by EIGRP for route calculation and neighbor relationship establishment. When mismatched k values are sent, they cause the receiving router to reject the neighbor announcement, potentially leading to neighbor flapping or complete neighbor shutdown. The goodbye message TLV manipulation allows attackers to send invalid termination signals that can trigger unexpected behavior in the routing protocol stack, ultimately resulting in the disruption of routing convergence and network connectivity.
From an operational impact perspective, this vulnerability can severely compromise network stability and availability, particularly in environments where EIGRP is the primary routing protocol. The denial of service condition can cause routers to continuously attempt to establish neighbor relationships, leading to increased CPU utilization and routing table instability. Network administrators may experience intermittent connectivity issues, routing loops, or complete routing protocol failures that can affect critical business operations. The remote nature of the attack means that adversaries do not require physical access or network credentials to exploit this weakness, making it particularly dangerous in publicly accessible network environments.
The vulnerability aligns with CWE-119, which addresses improper restriction of operations within a limited access scope, and demonstrates how insufficient input validation in network protocol implementations can lead to system instability. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network disruption and the T1562.001 technique for execution through privilege escalation or system manipulation. The attack vector requires minimal sophistication but can produce significant operational impact, making it attractive to threat actors seeking to disrupt network services.
Effective mitigation strategies include implementing Cisco IOS software patches that address the specific validation gaps in the EIGRP implementation, configuring access control lists to filter malicious neighbor announcements, and enabling authentication mechanisms for EIGRP neighbor relationships. Network administrators should also consider implementing monitoring solutions that can detect anomalous neighbor announcement patterns and automatically trigger alerts when suspicious k value mismatches or goodbye TLV manipulations are observed. Regular security assessments and network segmentation strategies can further reduce the attack surface and limit the potential impact of exploitation attempts.