Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to deny service over a network.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Management Services allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Local Session Manager (LSM) allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Graphics Kernel allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Tablet Windows User Interface (TWINUI) Subsystem allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Capability Access Management Service (camsvc) allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Graphics Kernel allows an authorized attacker to elevate privileges locally.
Concurrent execution using shared resource with improper synchronization ('race condition') in Printer Association Object allows an authorized attacker to elevate privileges locally.
virtualenv is a tool for creating isolated virtual python environments. Prior to version 20.36.1, TOCTOU (Time-of-Check-Time-of-Use) vulnerabilities in virtualenv allow local attackers to perform symlink-based attacks on directory creation operations. An attacker with local access can exploit a race condition between directory existence checks and creation to redirect virtualenv's app_data and lock file operations to attacker-controlled locations. This issue has been patched in version 20.36.1.
## Vulnerability Summary
**Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock
**Affected Component:** `filelock` package - `SoftFileLock` class
**File:** `src/filelock/_soft.py` lines 17-27
**CWE:** CWE-362, CWE-367, CWE-59
---
## Description
A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly.
The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service.
### Attack Scenario
```
1. Lock attempts to acquire on /tmp/app.lock
2. Permission validation passes
3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock
4. os.open() tries to create lock file
5. Lock operates on attacker-controlled target file or fails
```
---
## Impact
_What kind of vulnerability is it? Who is impacted?_
This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization.
**Affected Users:**
- Applications using `filelock.SoftFileLock` directly
- Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy)
**Consequences:**
- **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed
- **Denial of Service** - attacker can prevent lock file creation by maintaining symlink
- **Resource serialization failures** - multiple processes may acquire "locks" simultaneously
- **Unintended file operations** - lock could operate on attacker-controlled files
**CVSS v4.0 Score:** 5.6 (Medium)
**Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
**Attack Requirements:**
- Local filesystem access to the directory containing lock files
- Permission to create symlinks (standard for regular unprivileged users on Unix/Linux)
- Ability to time the symlink creation during the narrow race window
---
## Patches
_Has the problem been patched? What versions should users upgrade to?_
Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation.
**Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0)
**Mitigation Details:**
- The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support
- On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented
- On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented
**Users should:**
- Upgrade to the patched version when available
- For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock`
---
## Workarounds
_Is there a way for users to fix or remediate the vulnerability without upgrading?_
For users unable to update immediately:
1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146)
2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories:
```bash
chmod 700 /path/to/lock/directory
```
3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation
4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations
---
## References
_Are there any links users can visit to find out more?_
- **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock)
- **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html
- **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html
- **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html
- **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html
- **GitHub Repository:** https://github.com/tox-dev/filelock
---
**Reported by:** George Tsigourakos (@tsigouris007)
axios4go is a Go HTTP client library. Prior to version 0.6.4, a race condition vulnerability exists in the shared HTTP client configuration. The global `defaultClient` is mutated during request execution without synchronization, directly modifying the shared `http.Client`'s `Transport`, `Timeout`, and `CheckRedirect` properties. Impacted applications include that that use axios4go with concurrent requests (multiple goroutines, `GetAsync`, `PostAsync`, etc.), those where different requests use different proxy configurations, and those that handle sensitive data (authentication credentials, tokens, API keys). Version 0.6.4 fixes this issue.
filelock is a platform-independent file lock for Python. In versions prior to 3.20.1, a Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. All users of filelock on Unix, Linux, macOS, and Windows systems are impacted. The vulnerability cascades to dependent libraries. The attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. The issue is fixed in version 3.20.1. If immediate upgrade is not possible, use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases); ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks; and/or monitor lock file directories for suspicious symlinks before running trusted applications. These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended.