CVE-2011-0539 in OpenSSH
Summary
by MITRE
The key_certify function in usr.bin/ssh/key.c in OpenSSH 5.6 and 5.7, when generating legacy certificates using the -t command-line option in ssh-keygen, does not initialize the nonce field, which might allow remote attackers to obtain sensitive stack memory contents or make it easier to conduct hash collision attacks.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2011-0539 resides within the OpenSSH implementation, specifically in the key_certify function located in usr.bin/ssh/key.c. This flaw manifests when OpenSSH versions 5.6 and 5.7 generate legacy certificates using the -t command-line option through ssh-keygen. The core issue stems from improper initialization of the nonce field during certificate generation processes, creating a security exposure that affects the integrity and confidentiality of cryptographic operations.
The technical flaw represents a classic case of uninitialized memory usage, classified under CWE-457 as "Use of Uninitialized Variable." When the key_certify function processes certificate generation, it fails to properly initialize the nonce field before incorporating it into the cryptographic operations. This uninitialized memory segment may contain residual data from previous operations, potentially exposing stack contents that could include sensitive information such as cryptographic keys, session identifiers, or other confidential data. The vulnerability particularly impacts the generation of legacy certificates where the -t option is used to specify time-based certificates, making the uninitialized nonce field a vector for information disclosure.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could facilitate more sophisticated attacks including hash collision attempts. Attackers leveraging this flaw could potentially exploit the uninitialized nonce values to conduct hash collision attacks, where predictable or exposed nonce values might weaken the cryptographic strength of the generated certificates. This weakness undermines the fundamental security assumptions of certificate-based authentication systems, potentially allowing unauthorized parties to compromise the integrity of the certificate authority infrastructure. The vulnerability affects the security posture of systems relying on OpenSSH for certificate management, particularly in environments where legacy certificate generation is still in use.
Mitigation strategies for CVE-2011-0539 should prioritize immediate patching of affected OpenSSH versions to the latest stable releases that contain the fix for uninitialized nonce field handling. System administrators should also implement monitoring to detect any anomalous certificate generation patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1552.001 for unsecured credentials and T1071.004 for application layer protocol usage, as it affects the cryptographic security mechanisms that protect authentication processes. Organizations should conduct comprehensive vulnerability assessments to identify all systems running affected OpenSSH versions and ensure proper certificate management practices are implemented. Additionally, implementing proper memory initialization practices in cryptographic software development can prevent similar issues in future implementations, aligning with security best practices outlined in NIST SP 800-57 and ISO/IEC 27001 standards for cryptographic key management and secure software development practices.