# CVE-2026-112937: filelock: ReadWriteLock on the hard-link route deletes any directory another user renames onto its .filelock-* link directory name


- **Severity:** Medium 6.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 20 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-112937, ECHO-50ba-30e2-c806, GHSA-jqc4-5cvw-7w85, UBUNTU-CVE-2026-112937

## What is CVE-2026-112937?

CVE-2026-112937 is a medium-severity vulnerability in tox-dev filelock, published on 20 Oct 2026. 

### Official description

filelock is a platform-independent file lock for Python. From 4.1.0 until 4.2.1, ReadWriteLock can remove a randomized .filelock-* private-hard-link directory during cleanup, allowing another local user with rename access in a non-sticky parent to observe a live name or forge a dead-owner sweep name and rename a sibling directory onto it for deletion. This issue is fixed in version 4.2.1.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-112937?

2 open source packages ship an affected version, including filelock. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `filelock` | PyPI | From 4.1.0 | 4.2.1 |
| `filelock` | PyPI | From 4.1.0 | 4.2.1 |

Products: Tox-Dev Filelock.

## How do I fix CVE-2026-112937?

Upgrade filelock to 4.2.1 or later.

## Is CVE-2026-112937 being exploited?

There is no known exploitation of CVE-2026-112937 in the wild and no public exploit code.

## Other vulnerabilities in tox-dev filelock

- [CVE-2026-112940](https://insights.sbomify.com/CVE-2026-112940/): filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files (high 7.1)
- [CVE-2026-112911](https://insights.sbomify.com/CVE-2026-112911/): filelock: StrictSoftFileLock and SoftReadWriteLock adopt a protocol directory another user created first, losing mutual exclusion (medium 6.3)
- [CVE-2025-68146](https://insights.sbomify.com/CVE-2025-68146/): filelock has TOCTOU race condition that allows symlink attacks during lock file creation (medium 6.3)
- [CVE-2026-112909](https://insights.sbomify.com/CVE-2026-112909/): filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path (medium 6.1)
- [CVE-2026-112934](https://insights.sbomify.com/CVE-2026-112934/): filelock: SoftReadWriteLock holder refresh writes through a hard link and hangs on a named pipe that another local user renames over its record (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-112937 and fix it if it is affected.

What it is: CVE-2026-112937 is a medium-severity vulnerability in tox-dev filelock, published on 20 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-112937 in the wild and no public exploit code.

Affected packages and fixed versions:
- filelock (PyPI): affected from 4.1.0; fixed in 4.2.1
- filelock (PyPI): affected from 4.1.0; fixed in 4.2.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-112937/ (Markdown: https://insights.sbomify.com/CVE-2026-112937/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-112937
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-112937
- OSV: https://osv.dev/vulnerability/CVE-2026-112937

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-112937/
Summaries are generated and may contain mistakes; the official description above is the record.