CVE-2012-4099 in NX-OS
Summary
by MITRE
The BGP implementation in Cisco NX-OS does not properly filter AS paths, which allows remote attackers to cause a denial of service (BGP service reset and resync) via a malformed UPDATE message, aka Bug ID CSCtn13065.
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Analysis
by VulDB Data Team • 05/26/2021
The vulnerability described in CVE-2012-4099 represents a critical flaw in Cisco NX-OS BGP implementation that fundamentally undermines network stability and availability. This issue affects the Border Gateway Protocol implementation within Cisco's network operating system, specifically targeting how the system processes Autonomous System (AS) path information in BGP UPDATE messages. The flaw manifests when the system fails to properly validate and filter AS path attributes, creating a condition where malformed or specially crafted UPDATE messages can trigger unexpected behavior in the BGP service.
The technical mechanism behind this vulnerability involves the improper handling of AS path data structures within the BGP protocol implementation. When a remote attacker crafts a malicious UPDATE message containing malformed AS path information, the NX-OS BGP daemon processes this data without adequate validation checks. This processing failure leads to a service reset and subsequent resynchronization process that disrupts BGP peer connections and network routing stability. The vulnerability operates at the protocol level where BGP UPDATE messages carry routing information including AS paths that indicate the route a packet should take through the internet. When these paths contain unexpected or malformed data, the NX-OS implementation crashes or resets its BGP service state.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire network operations and routing integrity. Network administrators face the risk of unauthorized denial of service attacks that can cascade through BGP peer relationships, causing widespread routing instability across affected networks. The service reset and resync process creates temporary routing black holes and can result in significant network downtime while the BGP service recovers and re-establishes peer connections. This vulnerability particularly affects service providers and large enterprise networks that rely heavily on BGP for internet connectivity and inter-domain routing operations.
This vulnerability maps to CWE-129, which describes improper validation of input ranges, and aligns with ATT&CK technique T1498.001 for Network Denial of Service attacks. The flaw represents a classic input validation issue where the system fails to properly sanitize and validate BGP UPDATE message content before processing. Organizations implementing Cisco NX-OS should consider deploying network segmentation and access control measures to limit exposure to untrusted BGP peers. Additionally, implementing BGP monitoring and alerting systems can help detect anomalous UPDATE message patterns that may indicate exploitation attempts. The recommended mitigations include applying Cisco's security patches and updates, implementing BGP message filtering policies, and configuring proper access controls to restrict BGP peer relationships to trusted network entities. Network administrators should also consider implementing BGP route reflection and confederation strategies to reduce the attack surface and improve resilience against such denial of service conditions.