CVE-2012-4638 in IOS
Summary
by MITRE
Cisco IOS before 15.1(1)SY allows local users to cause a denial of service (device reload) by establishing an outbound SSH session, aka Bug ID CSCto00318.
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Analysis
by VulDB Data Team • 05/11/2026
Cisco IOS versions prior to 15.1(1)SY contain a critical vulnerability that enables local attackers to trigger a device reload through the establishment of outbound SSH sessions. This flaw represents a privilege escalation issue where authenticated local users can exploit a weakness in the SSH implementation to cause an unauthorized system restart. The vulnerability specifically manifests when the device attempts to establish outbound SSH connections, leading to a memory corruption condition that ultimately results in the device automatically reloading its operating system. This behavior creates a denial of service condition that can be exploited by any user with local access to the device, making it particularly dangerous in environments where local privileges are accessible to untrusted users. The underlying technical issue stems from improper handling of SSH session parameters during outbound connection establishment, where the system fails to properly validate or sanitize input data before processing. This vulnerability directly relates to CWE-122, which describes buffer overflow conditions, and falls under the broader category of memory corruption vulnerabilities that can lead to system instability and unauthorized access. The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged to create persistent denial of service attacks that may be difficult to detect and mitigate. Attackers can repeatedly establish and terminate SSH sessions to trigger the reload condition, potentially causing ongoing service interruptions that affect network availability and reliability. Organizations running affected Cisco IOS versions face significant risk of unauthorized device restarts that could disrupt critical network services, especially in environments where network infrastructure devices are not properly secured at the physical level. The vulnerability's exploitability is relatively straightforward, requiring only local authentication access and basic knowledge of SSH connectivity, making it accessible to a wide range of threat actors. Network administrators should implement immediate mitigations including applying the relevant Cisco security patches, restricting local access to devices, and monitoring for unusual SSH session patterns that may indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the execution of malicious code through system-level access. Additionally, this issue demonstrates the importance of proper input validation and secure coding practices in network infrastructure software, as the vulnerability could have been prevented through better handling of SSH session establishment parameters. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of local privilege escalation attacks on critical network infrastructure components. The vulnerability highlights the need for comprehensive security testing of network operating systems, particularly in areas related to session management and connection handling, as these components form critical pathways for both legitimate and malicious network communications.