CVE-2000-1137 in GNU
Summary
by MITRE
GNU ed before 0.2-18.1 allows local users to overwrite the files of other users via a symlink attack.
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Analysis
by VulDB Data Team • 06/25/2021
The vulnerability identified as CVE-2000-1137 affects GNU ed text editor versions prior to 0.2-18.1, representing a critical security flaw that enables local users to perform unauthorized file overwrites through symbolic link manipulation. This vulnerability specifically targets the file handling mechanisms within GNU ed, creating a privilege escalation scenario where malicious users can exploit the software's inability to properly validate file paths during operations. The flaw arises from insufficient input validation and improper handling of symbolic links, allowing attackers to manipulate the file system in ways that compromise data integrity and potentially lead to unauthorized access to other users' files.
The technical implementation of this vulnerability stems from GNU ed's failure to properly resolve symbolic links when performing file operations, particularly during file creation or modification processes. When a user executes an ed command that involves file operations, the software does not adequately verify whether the target path represents a symbolic link that could point to another user's file. This weakness creates a race condition scenario where an attacker can create a symbolic link with a name that matches a file the victim intends to modify, then exploit the timing window to overwrite the target file with malicious content. The vulnerability directly maps to CWE-59, which describes improper handling of symbolic links, and represents a classic example of a symlink attack that has been documented in various security contexts.
Operationally, this vulnerability presents significant risks to system security and data integrity within multi-user environments where GNU ed is installed. Local users who can execute ed commands can potentially overwrite files owned by other users, including system configuration files, user data, or sensitive documents. The impact extends beyond simple file corruption, as attackers could overwrite critical system files, leading to system instability or privilege escalation opportunities. The vulnerability is particularly dangerous in shared computing environments, web servers, or systems where multiple users have access to the same software installation. Attackers can leverage this weakness to gain unauthorized access to other users' data, modify system configurations, or create persistent backdoors by overwriting critical system files with malicious content.
Mitigation strategies for CVE-2000-1137 involve immediate software updates to versions 0.2-18.1 or later, which contain patches addressing the symbolic link handling issues. System administrators should also implement proper file permissions and access controls to limit the scope of potential damage, ensuring that users cannot create symbolic links in directories where sensitive files reside. Additional protective measures include monitoring for suspicious file creation patterns, implementing file integrity monitoring solutions, and conducting regular security audits to identify potential symlink attack vectors. From an operational security perspective, organizations should consider implementing privilege separation mechanisms and restricting the execution of ed commands to trusted users only. This vulnerability aligns with ATT&CK technique T1059.002, which covers command and scripting interpreter usage, and represents a common attack pattern in privilege escalation scenarios where local users exploit software weaknesses to gain unauthorized access to system resources.