CVE-2012-5036 in IOS
Summary
by MITRE
Cisco IOS before 12.2(50)SY1 allows remote authenticated users to cause a denial of service (memory consumption) via a sequence of VTY management sessions (aka exec sessions), aka Bug ID CSCtn43662.
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Analysis
by VulDB Data Team • 05/11/2026
Cisco IOS versions prior to 12.2(50)SY1 contain a vulnerability that enables remote authenticated attackers to consume excessive memory resources through a specific sequence of VTY management sessions. This flaw specifically affects the handling of exec sessions within the IOS operating system, creating a memory exhaustion condition that can lead to system denial of service. The vulnerability manifests when authenticated users establish multiple VTY sessions in a particular sequence that triggers improper memory management within the IOS kernel. The bug ID CSCtn43662 documents this specific weakness in the IOS implementation. This vulnerability represents a classic case of resource exhaustion attack where the attacker leverages legitimate authentication mechanisms to consume system resources beyond normal operational limits. The impact extends beyond simple service disruption as the memory consumption can potentially destabilize the entire IOS process, affecting other network services and protocols running on the same device. From a cybersecurity perspective, this vulnerability aligns with CWE-400 which categorizes unspecified resource management flaws, specifically targeting memory allocation and deallocation processes. The attack vector requires authentication, making it less likely to be exploited by casual attackers but still poses significant risk to network administrators who may not immediately recognize the resource consumption pattern. The vulnerability demonstrates a failure in proper session management and memory cleanup procedures within the IOS VTY subsystem. Organizations utilizing affected Cisco IOS versions face potential operational impacts including complete service outages, network management unavailability, and disruption of critical network infrastructure functions. The memory consumption pattern creates a gradual degradation that may not be immediately apparent, allowing the attack to persist undetected for extended periods. This flaw particularly affects network devices that rely heavily on remote management capabilities and multiple concurrent administrative sessions. The vulnerability can be exploited through normal network management operations, making it particularly dangerous as it leverages legitimate administrative functions to cause system instability. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers network denial of service attacks targeting network infrastructure. The attack requires minimal privileges since it only needs authenticated access to establish the problematic VTY session sequence. The memory consumption behavior creates a persistent threat that can be difficult to diagnose and remediate, as it may appear as normal system resource usage until the point of complete system failure. Network administrators should implement monitoring for unusual VTY session patterns and memory utilization spikes as early detection mechanisms. The vulnerability highlights the importance of proper session lifecycle management and memory deallocation in network operating systems. Cisco addressed this issue in the 12.2(50)SY1 software release through enhanced memory management routines and improved session handling protocols. The fix ensures proper cleanup of resources associated with VTY sessions and prevents the accumulation of memory that leads to system instability. Organizations should prioritize patching affected devices and implementing network segmentation to limit the potential impact of such vulnerabilities. Regular security assessments should include verification of IOS versions and patch status to prevent exploitation of known vulnerabilities. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date network operating system software and implementing robust network management practices.