CVE-2014-1624 in pyxdg
Summary
by MITRE
Race condition in the xdg.BaseDirectory.get_runtime_dir function in python-xdg 0.25 allows local users to overwrite arbitrary files by pre-creating /tmp/pyxdg-runtime-dir-fallback-victim to point to a victim-owned location, then replacing it with a symlink to an attacker-controlled location once the get_runtime_dir function is called.
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Analysis
by VulDB Data Team • 02/01/2022
The vulnerability described in CVE-2014-1624 represents a classic race condition flaw within the python-xdg library version 0.25, specifically affecting the xdg.BaseDirectory.get_runtime_dir function. This issue arises from improper handling of temporary file creation and directory management in a multi-threaded or multi-process environment where timing dependencies can be exploited by malicious actors. The flaw enables local privilege escalation through file overwrite operations that exploit the temporal window between file creation and symlink resolution. The vulnerability is particularly concerning as it affects a widely used library that implements the XDG Base Directory specification, which governs the standardization of directory locations for user-specific data in Linux and Unix-like systems.
The technical implementation of this race condition occurs when the get_runtime_dir function attempts to create a fallback runtime directory in the /tmp filesystem. The vulnerability stems from the library's failure to properly secure temporary file creation processes, allowing attackers to manipulate the filesystem state before the function completes its directory setup. When an attacker pre-creates a specific temporary file path /tmp/pyxdg-runtime-dir-fallback-victim with a symbolic link pointing to a location they control, they can effectively hijack the runtime directory creation process. This manipulation occurs because the function does not validate the integrity of the temporary path or implement proper atomic operations during directory creation, creating a window where the symlink can be replaced before the library's internal logic processes it.
The operational impact of this vulnerability extends beyond simple file overwrites, as it provides attackers with potential access to sensitive user data and system resources. When the get_runtime_dir function executes, it typically creates runtime directories for applications to store temporary files, sockets, and other runtime artifacts. By exploiting this race condition, an attacker can redirect this functionality to write data to arbitrary locations, potentially including configuration files, user data, or even system-critical files. The vulnerability affects any application that relies on python-xdg for managing XDG-compliant directory structures, making it particularly dangerous in environments where multiple applications interact with the same runtime directory mechanisms. This creates a cascading effect where a single compromised application could potentially compromise the entire system's runtime environment.
Mitigation strategies for this vulnerability require both immediate patching of the affected python-xdg library to version 0.26 or later, which implements proper race condition protections, and implementation of system-level security controls. System administrators should ensure all applications using python-xdg are updated to versions that address this specific race condition, typically through package management systems or direct library upgrades. The fix involves implementing atomic file creation operations, proper directory permission validation, and ensuring that temporary files are created with secure permissions that prevent symbolic link attacks. Additionally, organizations should consider implementing file system monitoring to detect suspicious symlink creation patterns and enforce proper privilege separation for applications that handle runtime directory creation. This vulnerability aligns with CWE-367, which addresses time-of-check to time-of-use (TOCTOU) race conditions, and represents a common attack vector categorized under ATT&CK technique T1059 for execution through command and scripting interpreters, as attackers may leverage this weakness to execute malicious code through manipulated runtime directories.