CVE-2012-4559 in libssh
Summary
by MITRE
Multiple double free vulnerabilities in the (1) agent_sign_data function in agent.c, (2) channel_request function in channels.c, (3) ssh_userauth_pubkey function in auth.c, (4) sftp_parse_attr_3 function in sftp.c, and (5) try_publickey_from_file function in keyfiles.c in libssh before 0.5.3 allow remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via unspecified vectors.
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Analysis
by VulDB Data Team • 12/20/2021
The CVE-2012-4559 vulnerability represents a critical class of memory corruption flaws affecting the libssh library version 0.5.2 and earlier. These double free vulnerabilities exist across multiple functions within the library's core components, specifically targeting the agent_sign_data function in agent.c, channel_request function in channels.c, ssh_userauth_pubkey function in auth.c, sftp_parse_attr_3 function in sftp.c, and try_publickey_from_file function in keyfiles.c. The vulnerability stems from improper memory management where the same memory block gets freed twice during different execution paths, creating a condition that can be exploited by remote attackers to manipulate the program's memory state.
These double free conditions occur when the library's authentication and channel management functions handle cryptographic operations and file processing without proper validation of memory allocation states. The flaw allows attackers to craft malicious input sequences that trigger the same memory block to be deallocated twice, leading to heap corruption that can result in program crashes or potentially arbitrary code execution. The vulnerability is particularly dangerous because it affects core authentication and file transfer operations within SSH implementations, making it exploitable during normal protocol interactions. The unspecified vectors indicate that attackers can leverage various attack surfaces within the library's protocol handling mechanisms.
The operational impact of CVE-2012-4559 extends beyond simple denial of service scenarios, as the heap corruption resulting from double free operations can enable remote code execution in certain conditions. This vulnerability directly affects systems implementing SSH protocols that rely on libssh for authentication and secure communication, potentially compromising the integrity of secure connections. The attack surface is broad since the affected functions handle common SSH operations including public key authentication, channel management, and SFTP file operations. Security researchers have classified these issues under CWE-415, which specifically addresses double free conditions in software development practices. The vulnerability aligns with ATT&CK technique T1059.007 for remote code execution through memory corruption, and T1499.004 for denial of service attacks targeting network services.
Mitigation strategies for CVE-2012-4559 require immediate patching of libssh installations to version 0.5.3 or later, where the double free conditions have been addressed through proper memory management practices. Organizations should implement comprehensive vulnerability scanning to identify systems running affected libssh versions and prioritize remediation efforts. Network segmentation and access controls can help limit potential exploitation by restricting access to SSH services. The fix typically involves implementing proper memory state validation before deallocation operations and ensuring that memory blocks are not freed multiple times during program execution. Security teams should also monitor for exploitation attempts through network intrusion detection systems that can identify crafted payloads targeting these specific memory corruption vulnerabilities in SSH implementations.