filelock: On Windows an oplock on a soft lock's marker holds SoftFileLock.acquire() past its timeout and blocks the stale break
- Exploited
- No known exploitation
- Fix
- Fixed in 4.2.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.2.1.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 23/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
A local attacker with low-privilege access on Windows can hold an oplock on a stale SoftFileLock marker, causing lock acquisition to hang past its timeout and blocking removal of the stale lock. Mutual exclusion stays intact and no other file is accessed, so the impact is limited to availability of the affected lock in filelock versions from 3.22.0 through 4.2.1.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, soft lock classes on Windows read an existing marker with _read_lock_file and remove a stale marker through break_lock_file using pathname operations that wait for an oplock break. Another local account with read access to an unheld marker can keep a Level 1 or batch oplock unanswered, causing SoftFileLock.acquire and related async or fallback locks to wait beyond timeout, blocking=False, and cancel_check. A stale marker under the oplock cannot be broken, but mutual exclusion remains intact and no file other than the marker is accessed. This issue is fixed in version 4.2.1.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach20/20filelock: 138.8M downloads a week
- Severity2.5/10CVSS 2.5
- No patch0/5No signal
What would change the score
- Would score about 78 if added to CISA KEV
- Would score about 73 if CISA's SSVC rates exploitation active
- Would score about 45 if advisories confirm default setups are exposed
Impact
- Widely used
filelock has 138.8m weekly downloads.Source: pypistats.org
47.2k packages depend on filelock.Source: deps.dev
What to do
Upgrade to a fixed version: 4.2.1.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- tox-dev filelock
From 3.22.0 · fixed in 4.2.1
- filelockPyPI
From 3.22.0 · fixed in 4.2.1
Evidence 5
- Advisory
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-112907
Is CVE-2026-112907 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-112907?
filelock: from 3.22.0 before 4.2.1. filelock (PyPI): from 3.22.0 before 4.2.1.Source: cve.now feed data
How do I fix CVE-2026-112907?
Upgrade to a fixed version: 4.2.1.Source: cve.now feed data