CVE-2012-5039 in IOS
Summary
by MITRE
The BGP Router process in Cisco IOS before 12.2(50)SY1 allows remote attackers to cause a denial of service (memory consumption) via vectors involving BGP path attributes, aka Bug ID CSCsw63003.
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Analysis
by VulDB Data Team • 05/11/2026
The vulnerability identified as CVE-2012-5039 represents a critical memory consumption issue within the Border Gateway Protocol (BGP) router process of Cisco IOS software. This flaw affects Cisco IOS versions prior to 12.2(50)SY1 and enables remote attackers to execute a denial of service attack by manipulating BGP path attributes. The vulnerability specifically impacts the routing process that handles BGP communications, which forms the backbone of internet routing and inter-domain connectivity. When exploited, this weakness allows an attacker to consume excessive memory resources on the affected router, ultimately leading to system instability and service disruption. The bug was catalogued as CSCsw63003, indicating its classification within Cisco's internal tracking system for security vulnerabilities.
The technical implementation of this vulnerability stems from insufficient input validation within the BGP path attribute processing mechanism. When a malicious actor sends specially crafted BGP updates containing malformed or excessive path attributes, the IOS router's BGP process fails to properly handle these inputs, resulting in uncontrolled memory allocation. This memory consumption occurs in a manner that does not properly account for the size or complexity of the incoming path attributes, allowing an attacker to gradually exhaust available memory resources on the device. The flaw operates at the protocol level, making it particularly dangerous as it can be exploited from any remote location capable of establishing BGP sessions with the vulnerable device, without requiring authentication or privileged access.
The operational impact of CVE-2012-5039 extends beyond simple service disruption to potentially compromise entire network infrastructures that rely on affected Cisco routers. Since BGP is fundamental to internet routing and inter-domain communication, a successful attack can cause widespread connectivity issues affecting multiple networks simultaneously. Network operators may experience complete loss of routing functionality, requiring manual intervention to restore normal operations through device rebooting or manual memory cleanup processes. The vulnerability's remote exploitability means that attackers can target devices from outside the organization's network perimeter, making it particularly dangerous for service providers and enterprises that maintain public BGP sessions. This type of denial of service attack can persist until the affected router is manually restarted or the software is patched, creating extended periods of network instability.
Organizations should implement immediate mitigation strategies including applying the relevant Cisco IOS patches that address this vulnerability, specifically upgrading to IOS version 12.2(50)SY1 or later. Network segmentation and access control measures should be strengthened to limit BGP session establishment to trusted peers only, reducing the attack surface. Monitoring systems should be enhanced to detect unusual memory consumption patterns and BGP update anomalies that may indicate exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of input length, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Additionally, implementing BGP security measures such as BGPsec or route filtering can provide additional protection layers against malicious BGP updates. Regular vulnerability assessments and network monitoring should be conducted to identify and remediate similar issues before they can be exploited by threat actors.