CVE-2001-0529 in OpenSSH
Summary
by MITRE
OpenSSH version 2.9 and earlier, with X forwarding enabled, allows a local attacker to delete any file named cookies via a symlink attack.
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability described in CVE-2001-0529 represents a critical security flaw in OpenSSH versions 2.9 and earlier that specifically affects systems with X forwarding enabled. This issue stems from improper handling of file operations during X11 forwarding sessions, creating a path traversal condition that allows local attackers to exploit symbolic link manipulation for unauthorized file deletion. The vulnerability specifically targets files named cookies, which are typically used for X11 authentication and session management within the SSH framework.
The technical implementation of this flaw occurs when OpenSSH processes X11 forwarding requests and creates temporary files in a predictable manner. When X forwarding is enabled, the system generates cookie files to maintain authentication state between the local X server and remote X applications. The vulnerability arises from the insecure creation of these cookie files, where the software does not properly validate or sanitize symbolic link references before performing file operations. Attackers can exploit this by creating malicious symbolic links that point to arbitrary files on the system, then triggering the X forwarding process to delete these target files through the cookie deletion mechanism.
This vulnerability operates under the broader category of insecure file handling and path traversal attacks, aligning with CWE-367 which addresses time-of-check to time-of-use (TOCTOU) race conditions. The operational impact of this flaw is significant as it allows local attackers to delete any file named cookies, potentially compromising system integrity and security. The attack vector specifically targets systems where users have local access and X forwarding is enabled, making it particularly dangerous in multi-user environments or when users maintain elevated privileges. The vulnerability essentially allows attackers to perform unauthorized file deletions through the legitimate SSH X forwarding process.
The security implications extend beyond simple file deletion, as this flaw can be leveraged to disrupt system services, remove critical authentication files, or create denial of service conditions. The exploitation requires local access to the system and knowledge of the X forwarding configuration, but once achieved, the impact can be substantial for system administrators who rely on SSH for secure remote access. This vulnerability demonstrates the importance of proper file handling practices in security-critical applications and highlights how seemingly benign features like X11 forwarding can introduce serious security risks when not properly implemented with adequate access controls and file validation mechanisms.
The recommended mitigations for this vulnerability include immediate upgrading to OpenSSH version 3.0 or later, which contains the necessary patches to address the symbolic link handling issue. System administrators should also disable X forwarding for users who do not require this functionality, particularly in environments where local privilege escalation is a concern. Additional protective measures include implementing proper file permissions, using secure temporary file creation methods, and conducting regular security audits of SSH configurations. The vulnerability serves as a reminder of the importance of following secure coding practices, particularly regarding file operations and symbolic link handling, as outlined in various security frameworks and best practices for system hardening.