CVE-2015-4155 in Parallel
Summary
by MITRE
GNU Parallel before 20150422, when using (1) --pipe, (2) --tmux, (3) --cat, (4) --fifo, or (5) --compress, allows local users to write to arbitrary files via a symlink attack on a temporary file.
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Analysis
by VulDB Data Team • 03/10/2018
GNU Parallel version 20150422 and earlier contains a critical local privilege escalation vulnerability that stems from improper handling of temporary files during execution of specific command line options. This vulnerability manifests when users employ the --pipe, --tmux, --cat, --fifo, or --compress flags, which create temporary files that are susceptible to symbolic link attacks. The flaw occurs because the application does not adequately validate the existence and ownership of temporary files before writing to them, allowing local attackers to craft malicious symbolic links that redirect file operations to arbitrary locations on the filesystem. This represents a classic race condition vulnerability where the temporary file creation and access phases are not properly synchronized, creating a window of opportunity for attackers to exploit.
The technical implementation of this vulnerability leverages the fundamental principle of symlink attacks where an attacker creates a symbolic link with the same name as a temporary file that GNU Parallel will later access. When the application executes with elevated privileges, such as when running in a setuid context or when the user has administrative permissions, the symbolic link redirection can cause the application to write sensitive data to locations chosen by the attacker rather than the intended temporary file location. This vulnerability is particularly dangerous because it can be exploited to overwrite critical system files, modify configuration data, or inject malicious content into files that are processed by the system. The vulnerability directly maps to CWE-377, which addresses insecure temporary file handling, and CWE-378, which covers creation of temporary files with insecure permissions.
The operational impact of this vulnerability extends beyond simple file system manipulation as it can enable attackers to escalate privileges and gain unauthorized access to system resources. When combined with other exploitation techniques, this vulnerability can serve as a foundational attack vector for more sophisticated compromise scenarios. The attack requires local system access but can be particularly damaging in environments where GNU Parallel is executed with elevated privileges or where users have the ability to run the application in contexts that provide extended permissions. Attackers can leverage this vulnerability to create persistent backdoors, modify system binaries, or manipulate critical configuration files that affect system behavior and security posture.
Mitigation strategies for this vulnerability require immediate patching of GNU Parallel to version 20150422 or later, which implements proper temporary file handling mechanisms including atomic file creation and validation of file ownership. System administrators should also implement additional controls such as restricting execution permissions for GNU Parallel in setuid contexts and monitoring for unusual file system access patterns that may indicate exploitation attempts. The use of privilege separation techniques and mandatory access controls can further reduce the impact of this vulnerability by limiting the scope of potential damage. Organizations should also consider implementing file integrity monitoring solutions that can detect unauthorized modifications to critical system files that may result from exploitation of this vulnerability. From an operational security perspective, regular security assessments should verify that all instances of GNU Parallel are updated to secure versions and that appropriate access controls are in place to prevent unauthorized execution of potentially vulnerable applications.