# CVE-2026-112912: filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker - **Severity:** Low 2.5 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N`) - **Exploited in the wild:** Not known - **Fix available:** Yes - **Published:** 20 Oct 2026 - **Updated:** 20 Oct 2026 - **Also known as:** CLEANSTART-2026-AQ00517, DEBIAN-CVE-2026-112912, GHSA-9j6q-wvj5-jgjg, UBUNTU-CVE-2026-112912 ## What is CVE-2026-112912? CVE-2026-112912 is a low-severity vulnerability in tox-dev filelock, published on 20 Oct 2026. ### Official description 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. Weakness: CWE-59 (Improper Link Resolution Before File Access) ## Which versions are affected by CVE-2026-112912? 2 open source packages ship an affected version, including filelock. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `filelock` | PyPI | From 3.32.6 | 4.2.1 | | `filelock` | PyPI | From 3.32.6 | 4.2.1 | Products: Tox-Dev Filelock. ## How do I fix CVE-2026-112912? Upgrade filelock to 4.2.1 or later. ## Is CVE-2026-112912 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-112912 exists. ## 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-2026-112912 and fix it if it is affected. What it is: CVE-2026-112912 is a low-severity vulnerability in tox-dev filelock, published on 20 Oct 2026. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-112912 exists. Affected packages and fixed versions: - filelock (PyPI): affected from 3.32.6; fixed in 4.2.1 - filelock (PyPI): affected from 3.32.6; 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-2026-112912/ (Markdown: https://insights.sbomify.com/CVE-2026-112912/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-112912 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-112912 - OSV: https://osv.dev/vulnerability/CVE-2026-112912 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-112912/ Summaries are generated and may contain mistakes; the official description above is the record.