CVE-2012-5014 in IOS
Summary
by MITRE
Cisco IOS before 15.1(2)SY allows remote authenticated users to cause a denial of service (device crash) by establishing an SSH session from a client and then placing this client into a (1) slow or (2) idle state, aka Bug ID CSCto87436.
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Analysis
by VulDB Data Team • 05/11/2026
Cisco IOS versions prior to 15.1(2) contain a critical vulnerability that enables authenticated remote attackers to trigger device crashes through carefully crafted SSH session management. This vulnerability specifically affects the SSH protocol implementation within the IOS operating system, where the device fails to properly handle client sessions that are placed into slow or idle states. The flaw manifests when an authenticated SSH client establishes a connection and subsequently enters a state where network communication becomes intermittent or suspended, causing the IOS device to become unresponsive and ultimately crash. This issue represents a classic buffer management and state handling problem that can be exploited to create persistent denial of service conditions. The vulnerability is particularly concerning because it requires only authenticated access, meaning that attackers with valid credentials can leverage this weakness to disrupt network operations. The root cause lies in how IOS processes SSH session states when network connectivity becomes unreliable or when clients exhibit behavior that does not conform to normal communication patterns. This weakness aligns with CWE-400 which addresses unspecified errors in resource management and represents a significant operational risk for network infrastructure. The impact extends beyond simple service disruption as device crashes can lead to extended network outages, requiring manual intervention to restore normal operations. Network administrators face the challenge of maintaining availability while dealing with this vulnerability that can be exploited through legitimate authentication mechanisms. The vulnerability also demonstrates weaknesses in the underlying protocol handling that could potentially be extended to affect other network services. Organizations running affected IOS versions must consider implementing immediate mitigations while planning for proper software updates to address the root cause. The issue highlights the importance of robust session management and proper handling of edge cases in network protocol implementations. This vulnerability can be particularly damaging in mission-critical environments where network availability is paramount, as it provides attackers with a straightforward method to cause service disruption. The attack vector requires minimal privileges and can be executed without sophisticated tools, making it a significant threat to network security. The vulnerability has been classified under the ATT&CK framework as a denial of service technique that leverages protocol implementation weaknesses to compromise system availability. Proper monitoring and logging of SSH sessions can help detect exploitation attempts, though the vulnerability itself requires software-level remediation. The affected versions represent a substantial portion of deployed IOS installations, making this a widespread concern for network security professionals. Organizations should prioritize patching efforts to avoid exploitation while also implementing network segmentation to limit the potential impact of successful attacks. The vulnerability underscores the critical importance of thorough testing of network protocol implementations under various stress and edge case conditions. This weakness demonstrates how seemingly minor implementation details in protocol handling can lead to catastrophic system failures and emphasizes the need for comprehensive security testing throughout the software development lifecycle. The vulnerability also represents a potential entry point for more complex attacks that could leverage the service disruption to gain additional access or escalate privileges within the network environment.