CVE-2012-4561 in libssh
Summary
by MITRE
The (1) publickey_make_dss, (2) publickey_make_rsa, (3) signature_from_string, (4) ssh_do_sign, and (5) ssh_sign_session_id functions in keys.c in libssh before 0.5.3 free "an invalid pointer on an error path," which might allow remote attackers cause a denial of service (crash) via unspecified vectors.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2012-4561 represents a critical memory management flaw within the libssh library version 0.5.2 and earlier. This issue affects multiple cryptographic functions including publickey_make_dss, publickey_make_rsa, signature_from_string, ssh_do_sign, and ssh_sign_session_id, all of which are located in the keys.c file. The vulnerability stems from improper handling of memory pointers during error conditions, specifically when the functions encounter invalid input data or unexpected processing scenarios. The flaw manifests when these functions free an invalid pointer reference on error paths, creating a potential for system instability and service disruption.
The technical implementation of this vulnerability involves the improper deallocation of memory resources within cryptographic signature processing workflows. When libssh encounters malformed or unexpected input data during key generation or signature operations, the affected functions attempt to free memory that may have already been deallocated or is otherwise invalid. This improper memory management creates a scenario where the application attempts to access freed memory locations, leading to segmentation faults or crashes. The vulnerability is particularly concerning because it can be triggered through various attack vectors involving malformed SSH protocol communications, making it exploitable by remote attackers without requiring authentication or elevated privileges.
From an operational perspective, this vulnerability creates significant denial of service risks for systems relying on libssh for secure communications. The remote attackers can cause service interruptions by sending specially crafted malformed data packets that trigger the invalid pointer freeing behavior. This creates cascading effects where legitimate users may be unable to establish secure connections to affected systems. The impact extends beyond simple service disruption as it can compromise the availability of critical infrastructure components that depend on SSH for secure remote access and management. Organizations running vulnerable versions of libssh face potential operational downtime and service degradation that can affect business continuity and system reliability.
The vulnerability aligns with CWE-415, which describes improper handling of memory allocation and deallocation, specifically addressing double free errors and invalid pointer dereferences. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, where attackers can leverage memory corruption flaws to disrupt service availability. The attack surface is broad as it affects any system using libssh for cryptographic operations, including servers, network appliances, and applications that implement SSH protocol support. Organizations should prioritize patching this vulnerability as it represents a straightforward exploit that can be automated and does not require specialized knowledge to execute.
Mitigation strategies include immediate upgrading to libssh version 0.5.3 or later, which contains the necessary memory management fixes. System administrators should also implement network monitoring to detect unusual traffic patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing intrusion detection systems that can identify malformed SSH protocol communications that could trigger this vulnerability. The patch addresses the root cause by ensuring proper memory handling during error conditions and prevents the freeing of invalid pointer references. Regular security assessments and vulnerability scanning should be conducted to identify other potentially vulnerable components within the system architecture that may be susceptible to similar memory management issues.