Source: secalert@redhat.com
virtualenv.py in virtualenv before 1.5 allows local users to overwrite arbitrary files via a symlink attack on a certain file in /tmp/.
Virtualenv versions prior to 1.5 are vulnerable to a symlink attack, allowing local users to overwrite arbitrary files. This vulnerability can lead to privilege escalation or system compromise by manipulating the creation of files within the virtual environment's temporary directory, potentially allowing attackers to inject malicious code or overwrite critical system files.
Step 1: Target Selection: The attacker identifies a target file on the system that can be overwritten to achieve a desired outcome (e.g., /etc/passwd for user account creation, or a configuration file for application compromise).
Step 2: Symlink Creation: The attacker creates a symbolic link (symlink) in the /tmp/ directory. This symlink points to the target file selected in Step 1.
Step 3: Virtualenv Trigger: The attacker initiates the creation or activation of a virtual environment using a vulnerable version of virtualenv.
Step 4: Race Condition Exploitation: During the virtual environment setup, virtualenv creates temporary files in /tmp/. The attacker's symlink intercepts the file creation process.
Step 5: File Overwrite: Virtualenv attempts to write to a file in /tmp/. Due to the symlink, this write operation is redirected to the target file, overwriting its contents with attacker-controlled data.
Step 6: Privilege Escalation/System Compromise: The overwritten file is now under the attacker's control, enabling them to achieve privilege escalation, inject malicious code, or otherwise compromise the system.
The vulnerability stems from a race condition in how virtualenv handles file creation within the /tmp/ directory. Specifically, virtualenv creates temporary files and directories during the virtual environment setup process. An attacker can exploit this by creating a symlink pointing from a file within the /tmp/ directory (where virtualenv creates temporary files) to a critical system file. When virtualenv attempts to create or write to a file in /tmp/, the attacker's symlink redirects the write operation to the target system file. This allows the attacker to overwrite the target file with attacker-controlled content. The root cause is the lack of proper validation and sanitization of file paths and the absence of checks to prevent symlink attacks during the file creation process. The use of /tmp/ as a temporary directory, combined with insufficient security checks, creates a window of opportunity for the attacker to manipulate file creation and overwrite arbitrary files.
While no specific APT groups are directly associated with this specific CVE, the techniques employed (symlink attacks) are common. This vulnerability could be leveraged by attackers with local access to a system. This is not listed in CISA KEV.
Monitor file system activity for suspicious symlink creation, especially within the /tmp/ directory.
Analyze system logs for unexpected file modifications, particularly those affecting critical system files.
Implement file integrity monitoring (FIM) to detect unauthorized changes to critical files.
Review virtualenv installation logs for any errors or unusual behavior during environment creation or activation.
Network traffic analysis may not be directly relevant, but unusual process behavior might be indicative of compromise.
Upgrade to virtualenv version 1.5 or later.
Implement file path validation and sanitization to prevent symlink attacks.
Use a more secure temporary directory that is not world-writable.
Regularly audit and update all installed Python packages, including virtualenv.
Enforce least privilege principles, limiting the permissions of users and processes.
Implement file integrity monitoring to detect unauthorized changes.