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Response snapshot Oct 29, 2026, 02:31 UTC

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VulnerabilityCVE-2026-112936

filelock: ReadWriteLock follows a symlink at the lock path into SQLite

ReadWriteLock and AsyncReadWriteLock resolve the lock path with pathlib.Path.resolve() and pass it to sqlite3.connect() without refusing a symlink.

Published Updated

At a glance

Exploited
Not known
Severity
6.1 Medium (CVSS 3.1)
Chance of exploitation
0.2% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: filelock: 4.0.9. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-j8f7-rjxc-mr56 (opens a new tab)

What happened

Summary

ReadWriteLock and AsyncReadWriteLock resolve the lock path with pathlib.Path.resolve() and pass it to sqlite3.connect() without refusing a symlink. A local user who can create names in the lock's directory, such as /tmp or a shared cache, can plant a symlink at the lock path and make the victim's process create, lock, or write the file it points to, or break mutual exclusion between the victim's own processes.

Details

ReadWriteLock.init stores pathlib.Path(lock_file).resolve(), which follows a final symlink, and every connection opens that path through sqlite3.connect() with no O_NOFOLLOW or regular-file check. SQLite's own VFS also resolves the final symlink in user space, so fs.protected_symlinks and the sticky bit do not help: the kernel never sees a symlink to refuse.

Continue reading

The other lock classes do not follow a final symlink: FileLock opens with O_NOFOLLOW, and SoftReadWriteLock coordinates through .rw/.

Proof of concept

On Linux, with the victim and attacker as different users and /shared mode 1777 with fs.protected_symlinks=1:

1. The attacker runs ln -s /home/victim/private/pwned.flag /shared/app.rwlock.db. 2. The victim constructs ReadWriteLock("/shared/app.rwlock.db"). A plain os.open(..., O_NOFOLLOW) on the same path fails, but the lock creates /home/victim/private/pwned.flag, owned by the victim, inside a directory the attacker cannot write. 3. With /shared/cache.rwlock.db -> /shared/a.db, one victim process holds the write lock.

The attacker repoints the link to /shared/b.db, and a second victim process acquires the write lock while the first still holds it.

The same behavior reproduces on macOS, on Windows 11, and through AsyncReadWriteLock.

Impact

A local attacker with write access to the lock directory can make the victim create empty files it owns at paths the attacker cannot write, make the victim hold a SQLite lock on another application's database so that application gets database is locked, and give two victim processes the write lock at once, letting them corrupt the resource the lock protects.

Workarounds

Keep ReadWriteLock paths in directories that only trusted users can write.

Affected package ranges reported by GitHub: filelock: >= 3.20.4, <= 4.0.8

Scores and how they were measured

CVSS base severity

6.1

Version 3.1As of

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.2%

Scored Percentile 14.1%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Follow Python packages (PyPI): RSS feedAll its recordsAsk your AI assistant

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-j8f7-rjxc-mr56 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-j8f7-rjxc-mr56, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-112936, scored 2026-10-28. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). filelock: ReadWriteLock follows a symlink at the lock path into SQLite (CVE-2026-112936). https://kevwire.com/record/CVE-2026-112936

MLA

"filelock: ReadWriteLock follows a symlink at the lock path into SQLite (CVE-2026-112936)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-112936.

Chicago

KEVWire. "filelock: ReadWriteLock follows a symlink at the lock path into SQLite (CVE-2026-112936)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-112936.

Evidence summary (plain text)

filelock: ReadWriteLock follows a symlink at the lock path into SQLite (Oct 28, 2026).
ReadWriteLock and AsyncReadWriteLock resolve the lock path with pathlib.Path.resolve() and pass it to sqlite3.connect() without refusing a symlink. A local user who can create names in the lock's directory, such as /tmp or a shared cache, can plant a symlink at the lock path and make the victim's process create, lock, or write the file it points to, or break mutual exclusion between the victim's own processes.
CVSS 6.1 (version 3.1; evidence as of Oct 28, 2026; https://github.com/advisories/GHSA-j8f7-rjxc-mr56).
EPSS 0.2% for the following 30 days, scored Oct 28, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-112936&date=2026-10-28).
Sources:
GitHub-reviewed advisory GHSA-j8f7-rjxc-mr56: https://github.com/advisories/GHSA-j8f7-rjxc-mr56
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-112936&date=2026-10-28
Record ID: CVE-2026-112936.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 02:16 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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