---
id: "CVE-2026-112912"
kind: "vulnerability"
aliases: ["CVE-2026-112912"]
title: "filelock: symlink race lets local users probe file writability"
severity: "low"
cvss: 2.5
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "tox-dev filelock", "fixed": ["4.2.1"], "affected": ">= 3.32.6, < 4.2.1", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["filelock", "local-multi-user", "package", "python"]
not_affected_if: ["filelock-below-3.32.6", "no-softfilelock", "single-user-host"]
published_at: "2026-10-20T15:17:15+00:00"
first_seen_at: "2026-10-23T21:57:20+00:00"
updated_at: "2026-10-25T04:49:34+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112912", "first_seen_at": "2026-10-23T21:57:20+00:00"}]
---

# filelock: symlink race lets local users probe file writability

SoftFileLock in filelock versions 3.32.6 through 4.2.1 can follow a swapped symbolic link during its writability check. A local user can infer whether a chosen path exists and is writable from whether the lock acquisition succeeds.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:tox-dev filelock affected >= 3.32.6, < 4.2.1 fixed 4.2.1

## How to check

- Run `pip show filelock` or `python -c "import filelock; print(filelock.__version__)"` and check whether the version is at least `3.32.6` and below `4.2.1`.
- Check whether the project pins filelock in a lock file such as `requirements.txt`, `poetry.lock` or `uv.lock`.

## Fix

- Upgrade filelock to `4.2.1` or later.

## Timeline

- 2026-10-23T21:57:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112912

## From the sources

filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition result. This issue is fixed in version 4.2.1.

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