CVE-2011-3273 in IOS
Summary
by MITRE
Memory leak in Cisco IOS 15.0 through 15.1, when IPS or Zone-Based Firewall (aka ZBFW) is configured, allows remote attackers to cause a denial of service (memory consumption or device crash) via vectors that trigger many session creation flows, aka Bug ID CSCti79848.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/23/2021
The vulnerability identified as CVE-2011-3273 represents a critical memory leak issue affecting Cisco IOS versions 15.0 through 15.1 when specific security features are enabled. This flaw manifests when the Intrusion Prevention System or Zone-Based Firewall components are configured, creating a condition where remote attackers can exploit the system through excessive session creation attempts. The vulnerability is catalogued under the Cisco bug ID CSCti79848 and demonstrates how security features designed to protect network infrastructure can themselves become attack vectors when improperly implemented. The memory leak occurs during normal operational conditions when the system processes multiple concurrent session creation flows, leading to gradual memory exhaustion that ultimately results in device instability and potential complete system failure.
The technical root cause of this vulnerability lies in the improper handling of memory allocation within the IOS processing pipeline when IPS or ZBFW modules are active. When numerous session creation requests are processed in rapid succession, the system fails to properly release allocated memory blocks back to the available pool, causing progressive memory consumption over time. This memory management flaw operates at the kernel level within the IOS operating system, where session state information is stored in dynamically allocated memory segments. The vulnerability specifically affects the session table management mechanism, where each new session creation consumes memory resources without adequate garbage collection or memory reclamation processes. The issue is particularly exacerbated when the system is under stress from legitimate traffic patterns that generate high session volume, making it difficult to distinguish between normal operational load and malicious exploitation attempts. This flaw directly corresponds to CWE-401, which identifies improper memory management as a critical weakness in software systems.
The operational impact of CVE-2011-3273 extends far beyond simple service disruption, as it can lead to complete device outages that compromise network availability and reliability. Remote attackers can systematically consume available memory resources through carefully crafted session creation sequences, eventually causing the device to crash or become unresponsive to legitimate traffic. Network administrators may observe gradual performance degradation before complete system failure, making early detection challenging. The vulnerability affects critical network infrastructure components including routers and switches running affected IOS versions, potentially disrupting large-scale network operations and creating cascading failures across interconnected systems. The attack vector requires no authentication and can be executed from remote locations, making it particularly dangerous for publicly accessible network devices. This vulnerability aligns with ATT&CK technique T1499.004, which describes network denial of service attacks targeting system resources, and represents a classic example of how insufficient resource management in security implementations can create exploitable conditions.
Mitigation strategies for CVE-2011-3273 require immediate implementation of both operational and configuration-based controls to prevent exploitation. Organizations should prioritize applying the relevant Cisco security patches and IOS updates that address the memory leak conditions in the IPS and ZBFW modules. Network administrators must consider disabling or temporarily removing the problematic security features when operating in high-risk environments until proper patches are deployed. Implementing rate limiting and session monitoring mechanisms can help detect abnormal session creation patterns that may indicate exploitation attempts. The configuration of proper logging and alerting systems becomes crucial to identify when memory consumption reaches critical levels, allowing for proactive intervention before complete system failure occurs. Additionally, network segmentation strategies should be employed to limit the potential impact of successful attacks, ensuring that exploitation of this vulnerability does not compromise entire network infrastructures. Regular monitoring of system memory usage and performance metrics provides early warning capabilities, while maintaining detailed audit trails helps establish attack patterns and supports incident response activities. The vulnerability demonstrates the importance of thorough testing of security features in production environments and highlights the need for robust memory management practices in network operating systems, particularly in the context of security modules that handle high-volume traffic processing operations.