CVE-2011-4327 in OpenSSH
Summary
by MITRE
ssh-keysign.c in ssh-keysign in OpenSSH before 5.8p2 on certain platforms executes ssh-rand-helper with unintended open file descriptors, which allows local users to obtain sensitive key information via the ptrace system call.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability described in CVE-2011-4327 represents a critical security flaw in the OpenSSH implementation that affects systems running versions prior to 5.8p2. This issue specifically targets the ssh-keysign component which is designed to facilitate secure key signing operations within the SSH framework. The vulnerability stems from improper handling of file descriptors during the execution of the ssh-rand-helper utility, creating an unexpected security exposure that could be exploited by local attackers to extract sensitive cryptographic information. The flaw is particularly concerning because it leverages the ptrace system call, which is commonly used for debugging and process tracing operations, making it a well-known and accessible attack vector for malicious actors with local system access.
The technical implementation of this vulnerability involves the ssh-keysign utility executing ssh-rand-helper with file descriptors that remain open and accessible to the calling process. When ssh-keysign runs on certain platforms, it does not properly close or manage the file descriptors inherited from the parent process, allowing these descriptors to persist and potentially expose sensitive information. The ptrace system call becomes instrumental in this attack as it enables a local user to attach to the running ssh-keysign process and access the open file descriptors that contain cryptographic keys or other sensitive data. This represents a classic case of improper resource management where the system fails to properly isolate and secure sensitive data during process execution, creating an information disclosure vulnerability that can lead to the compromise of cryptographic keys used for authentication and encryption purposes.
The operational impact of this vulnerability extends beyond simple information disclosure as it fundamentally undermines the security of SSH-based authentication systems. Local attackers who can execute code on the target system can leverage this flaw to extract private cryptographic keys that are used for SSH key authentication, potentially enabling them to impersonate legitimate users or gain unauthorized access to systems protected by SSH. The vulnerability is particularly dangerous in multi-user environments where local access is common, as it allows any user with local privileges to potentially compromise the security of the entire SSH infrastructure. According to CWE classification, this vulnerability maps to CWE-200, which deals with exposure of sensitive information to an unauthorized actor, and the ATT&CK framework would categorize this under privilege escalation and credential access techniques where adversaries exploit local system weaknesses to obtain sensitive information.
Mitigation strategies for CVE-2011-4327 primarily focus on upgrading to OpenSSH version 5.8p2 or later, where the file descriptor handling has been corrected to prevent the unintended exposure of sensitive information. System administrators should also implement proper access controls and privilege separation to limit the potential impact of local attackers who might attempt to exploit this vulnerability. Additional defensive measures include monitoring for unauthorized ptrace operations and implementing process monitoring to detect suspicious activities related to ssh-keysign and ssh-rand-helper processes. Organizations should also consider implementing file system permissions and access controls that prevent unauthorized access to sensitive system files and processes that might be involved in cryptographic operations. The vulnerability highlights the importance of proper resource management in security-critical applications and demonstrates how seemingly minor implementation flaws can have significant security implications.