CVE-2002-2053 in IOS
Summary
by MITRE
The design of the Hot Standby Routing Protocol (HSRP), as implemented on Cisco IOS 12.1, when using IRPAS, allows remote attackers to cause a denial of service (CPU consumption) via a router with the same IP address as the interface on which HSRP is running, which causes a loop.
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Analysis
by VulDB Data Team • 09/03/2019
The vulnerability described in CVE-2002-2053 represents a critical design flaw in the Hot Standby Routing Protocol implementation within Cisco IOS 12.1 systems. This issue specifically manifests when HSRP operates in conjunction with IRPAS functionality, creating a scenario where malicious actors can exploit the protocol's handling of duplicate IP addresses to trigger excessive CPU consumption. The vulnerability stems from the protocol's inability to properly manage situations where multiple routers attempt to assume the same IP address role within the same network segment, leading to a condition that can be exploited to cause significant performance degradation.
The technical root cause of this vulnerability lies in how HSRP processes router advertisements and state transitions when duplicate IP addresses are detected on the network. When a router configured with HSRP receives a packet from another device claiming the same IP address as the HSRP virtual IP, the protocol's state machine enters a problematic loop where it continuously attempts to resolve the conflict. This creates a scenario where the router's CPU resources become consumed in an endless cycle of processing these conflicting advertisements, ultimately leading to a denial of service condition that affects the entire network segment. The flaw is particularly dangerous because it can be triggered remotely without requiring authentication or specialized privileges, making it an attractive target for network-level attacks.
From an operational perspective, this vulnerability presents a severe threat to network availability and stability. When exploited, the affected router consumes excessive CPU cycles, potentially leading to complete service disruption for network traffic that relies on HSRP for redundancy. The loop condition created by the protocol's response to duplicate IP addresses can cause the router to become unresponsive, effectively breaking the high availability guarantee that HSRP is designed to provide. Network administrators may experience sudden and unexplained performance degradation, with the affected router becoming a bottleneck that prevents normal traffic flow. This vulnerability directly impacts the availability aspect of the CIA triad, compromising the network's ability to provide continuous service to legitimate users.
The impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire network infrastructure's reliability. When multiple routers in a network segment are affected by this issue, it can create cascading failures that propagate throughout the network topology. The attack vector is particularly concerning as it requires no privileged access and can be executed from any location within the network segment, making it difficult to detect and prevent. This vulnerability aligns with CWE-362 in the Common Weakness Enumeration, which identifies concurrent execution with improper synchronization as a weakness that can lead to denial of service conditions. The behavior also maps to attack techniques in the MITRE ATT&CK framework under the category of "Denial of Service" where adversaries exploit protocol implementations to consume system resources.
Mitigation strategies for this vulnerability should focus on implementing proper network segmentation and access control measures to prevent unauthorized devices from participating in HSRP operations. Network administrators should ensure that only authorized routers are permitted to participate in HSRP groups and implement monitoring systems to detect unusual CPU usage patterns that may indicate exploitation attempts. Cisco has released specific patches and firmware updates to address this vulnerability, which should be applied immediately to all affected systems. Additionally, implementing rate limiting on router advertisement messages and configuring proper authentication mechanisms for HSRP can help reduce the attack surface. Network segmentation strategies that isolate HSRP groups and limit the scope of potential attacks are also recommended to contain the impact should exploitation occur. The vulnerability demonstrates the importance of thorough protocol design reviews and the need for robust error handling in network infrastructure components to prevent exploitation scenarios that can lead to complete service disruption.