CVE-2021-23239 in sudo
Summary
by MITRE • 01/12/2021
The sudoedit personality of Sudo before 1.9.5 may allow a local unprivileged user to perform arbitrary directory-existence tests by winning a sudo_edit.c race condition in replacing a user-controlled directory by a symlink to an arbitrary path.
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Analysis
by VulDB Data Team • 05/16/2025
The vulnerability identified as CVE-2021-23239 affects the sudoedit functionality within the Sudo command-line utility version 1.9.5 and earlier. This represents a significant local privilege escalation risk that exploits a race condition in the sudoedit implementation. The flaw specifically impacts systems where unprivileged users can leverage the sudoedit personality to manipulate directory structures, creating a pathway for unauthorized access to restricted system resources. The vulnerability stems from insufficient synchronization mechanisms during file replacement operations, allowing malicious actors to exploit timing windows in the system's handling of user-controlled directories.
The technical implementation of this vulnerability resides in the sudo_edit.c source file where a race condition occurs during the replacement of user-controlled directories. When a user invokes sudoedit with certain parameters, the system creates temporary directories and performs file operations that can be manipulated by an attacker who controls the directory structure. The race condition manifests when an attacker can successfully replace a directory with a symbolic link pointing to an arbitrary location before the sudoedit process completes its operations. This timing issue enables attackers to bypass normal access controls and potentially gain elevated privileges. The flaw aligns with CWE-367, which addresses time-of-check to time-of-use vulnerabilities, where the system state changes between verification and actual use of resources. The race condition specifically enables directory traversal attacks that can be exploited to access files outside the intended scope of the sudoedit operation.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential data exposure and system compromise. An unprivileged local user who can execute sudoedit commands can leverage this flaw to perform arbitrary directory existence tests, effectively bypassing access controls and potentially gaining access to sensitive system files or directories. This capability allows for reconnaissance activities and can serve as a stepping stone for further exploitation within the system. The vulnerability affects Unix-like systems where Sudo is installed and where users have the ability to invoke sudoedit functionality, making it particularly concerning in multi-user environments where privilege separation is critical. Attackers can use this vulnerability to enumerate system directories, access restricted files, and potentially escalate privileges to root level access. The exploitability of this vulnerability requires local access and the ability to invoke sudoedit, but once successful, it can provide attackers with significant system control capabilities.
Mitigation strategies for CVE-2021-23239 focus primarily on upgrading to Sudo version 1.9.5 or later, where the race condition has been addressed through improved synchronization mechanisms and proper handling of directory operations. System administrators should implement immediate patching protocols to ensure all affected systems are updated. Additional defensive measures include reviewing sudoers configuration files to minimize unnecessary sudoedit usage, implementing proper file system permissions, and monitoring for suspicious directory creation patterns. The mitigation approach aligns with ATT&CK technique T1068 which covers local privilege escalation through race conditions and timing vulnerabilities. Organizations should also consider implementing automated patch management systems to prevent similar vulnerabilities from affecting their infrastructure. Security monitoring should include detection of symlink creation patterns and unusual directory operations that could indicate exploitation attempts. Regular security audits of sudo configurations and privilege escalation mechanisms remain essential for maintaining system integrity and preventing exploitation of similar timing-based vulnerabilities in other system components.