CVE-2006-5051 in OpenSSH
Summary
by MITRE
Signal handler race condition in OpenSSH before 4.4 allows remote attackers to cause a denial of service (crash), and possibly execute arbitrary code if GSSAPI authentication is enabled, via unspecified vectors that lead to a double-free.
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Analysis
by VulDB Data Team • 12/17/2024
The vulnerability identified as CVE-2006-5051 represents a critical race condition flaw within the OpenSSH implementation that existed prior to version 4.4. This vulnerability specifically affects the signal handling mechanisms within the sshd daemon when GSSAPI authentication is enabled, creating a potential pathway for remote attackers to exploit the system through a double-free memory error. The race condition occurs during the processing of signals that are generated during the authentication process, particularly when GSSAPI is utilized, which allows for the integration of external authentication mechanisms such as Kerberos.
The technical nature of this vulnerability stems from improper synchronization of signal handlers within the OpenSSH server implementation, where concurrent access to shared memory resources during authentication operations can lead to unpredictable behavior. When GSSAPI authentication is active, the system's signal handling routines may be invoked simultaneously from multiple execution paths, causing memory management functions to be called twice on the same memory block. This double-free condition creates a scenario where freed memory is accessed or reallocated, potentially leading to memory corruption that can be leveraged by attackers to cause system crashes or in some cases, execute arbitrary code within the context of the sshd process.
The operational impact of this vulnerability extends beyond simple denial of service, as the potential for arbitrary code execution makes it particularly dangerous in environments where OpenSSH serves as a primary authentication mechanism. Attackers exploiting this vulnerability can cause the sshd daemon to crash and restart repeatedly, leading to service disruption, or more critically, gain elevated privileges within the system if they can successfully leverage the memory corruption to inject malicious code. The vulnerability is particularly concerning because it requires minimal prerequisites for exploitation, as GSSAPI authentication is often enabled in enterprise environments, and the attack can be executed remotely without requiring prior authentication.
Mitigation strategies for this vulnerability primarily involve upgrading to OpenSSH version 4.4 or later, where the race condition has been addressed through improved signal handling mechanisms and proper memory management practices. System administrators should also consider disabling GSSAPI authentication if it is not required for their specific use case, as this eliminates the attack surface associated with the vulnerable code path. Additionally, implementing network segmentation and access controls can help reduce the exposure of SSH services to potential attackers, while regular security audits should verify that all systems have been patched and that authentication mechanisms are properly configured. This vulnerability aligns with CWE-362, which describes a race condition, and represents a specific implementation weakness that can be addressed through proper synchronization techniques and memory management practices. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service tactics, as it enables both service disruption and potential code execution within the target system.