CVE-2012-0386 in IOS
Summary
by MITRE
The SSHv2 implementation in Cisco IOS 12.2, 12.4, 15.0, 15.1, and 15.2 and IOS XE 2.3.x through 2.6.x and 3.1.xS through 3.4.xS before 3.4.2S allows remote attackers to cause a denial of service (device reload) via a crafted username in a reverse SSH login attempt, aka Bug ID CSCtr49064.
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Analysis
by VulDB Data Team • 03/22/2021
The vulnerability described in CVE-2012-0386 represents a critical denial of service flaw within Cisco IOS and IOS XE implementations that affects multiple software versions including 12.2, 12.4, 15.0, 15.1, 15.2 and various IOS XE releases. This issue specifically targets the SSHv2 protocol implementation and manifests when a remote attacker crafts a malicious username during a reverse SSH login attempt. The vulnerability operates at the network infrastructure level where Cisco devices running affected software versions become susceptible to deliberate disruption through carefully constructed authentication attempts that exploit implementation weaknesses in the Secure Shell protocol handling.
The technical flaw stems from insufficient input validation within the SSHv2 authentication process where the system fails to properly handle malformed or crafted usernames during reverse SSH connections. When a specially crafted username is submitted as part of the authentication sequence, the device's SSH implementation becomes vulnerable to a buffer overflow condition or memory corruption that ultimately leads to system instability. This type of vulnerability aligns with CWE-121 which describes heap-based buffer overflow conditions, and represents a classic example of improper input validation that can be exploited to cause system crashes. The flaw specifically impacts the SSH server implementation within Cisco's IOS operating system where authentication requests are processed without adequate boundary checking on user-provided data.
The operational impact of this vulnerability extends beyond simple service disruption as it can lead to complete device reloads and network outages across affected Cisco infrastructure. When exploited successfully, the vulnerability forces network administrators to deal with unexpected device restarts that can cascade through network operations, particularly in environments where redundant or failover mechanisms depend on stable SSH connectivity. The reverse SSH login scenario is particularly concerning as it allows attackers to target devices without requiring direct network access to the device itself, making the attack surface broader and more difficult to defend against. This vulnerability can be classified under ATT&CK technique T1499.004 which covers network denial of service attacks, and represents a significant threat to network availability and operational continuity.
Mitigation strategies for CVE-2012-0386 should prioritize immediate software patching of all affected Cisco IOS and IOS XE versions to address the underlying SSH implementation flaw. Network administrators should implement access controls to restrict SSH access to trusted networks and consider disabling reverse SSH functionality where possible. Additionally, monitoring systems should be configured to detect unusual authentication patterns or repeated failed login attempts that may indicate exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date network infrastructure software and implementing robust network segmentation to limit the potential impact of such flaws. Organizations should also consider implementing network-based intrusion detection systems that can identify and alert on suspicious SSH traffic patterns that may indicate exploitation attempts against this specific vulnerability.