{"id":"CVE-2026-112911","kind":"vulnerability","aliases":["CVE-2026-112911"],"related":[],"title":"filelock: local users can break lock state in shared directories","description":"filelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, StrictSoftFileLock versions from 3.30.0 and SoftReadWriteLock versions from 4.0.0 can adopt a protocol directory created first by another local user in a shared parent directory, allowing that user to alter protocol state and admit concurrent holders. This issue is fixed in version 4.2.1.","summary":"filelock is a Python library for cross-process file locks. Between versions 3.30.0 and 4.2.1, StrictSoftFileLock and SoftReadWriteLock can adopt a lock directory created first by another local user in a shared parent directory, letting that user alter lock state and let concurrent holders in.","severity":"medium","cvss":6.3,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"tox-dev filelock","fixed":["4.2.1"],"affected":">= 3.30.0, < 4.2.1","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["filelock","multi-user-hosts","package","python","shared-tmp"],"not_affected_if":["other-lock-classes","private-lock-directory","single-user-host"],"how_to_check":"- Run `pip show filelock` or `pip freeze | grep -i filelock` and check whether the version is at least `3.30.0` and below `4.2.1`.\n- Check whether code uses `StrictSoftFileLock` or `SoftReadWriteLock` with lock paths in a shared directory such as `/tmp`.","fix":"- Upgrade filelock to `4.2.1` or later.\n- Until upgraded, keep lock paths in directories only the application user can write to.","status":"open","published_at":"2026-10-20T15:17:15+00:00","first_seen_at":"2026-10-23T21:57:20+00:00","triaged_at":"2026-10-25T04:01:36+00:00","updated_at":"2026-10-25T04:01:36+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-25T04:01:36Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade filelock to `4.2.1` or later.\n- Until upgraded, keep lock paths in directories only the application user can write to.","reach":"local","title":"filelock: local users can break lock state in shared directories","impact":"medium","summary":"filelock is a Python library for cross-process file locks. Between versions 3.30.0 and 4.2.1, StrictSoftFileLock and SoftReadWriteLock can adopt a lock directory created first by another local user in a shared parent directory, letting that user alter lock state and let concurrent holders in.","category":"package","nicknames":[],"who_cares":["python","filelock","multi-user-hosts","shared-tmp"],"confidence":0.7,"needs_auth":"yes","worst_case":"local user alters lock state and admits concurrent holders","analyst_note":"","how_to_check":"- Run `pip show filelock` or `pip freeze | grep -i filelock` and check whether the version is at least `3.30.0` and below `4.2.1`.\n- Check whether code uses `StrictSoftFileLock` or `SoftReadWriteLock` with lock paths in a shared directory such as `/tmp`.","needs_analyst":false,"not_affected_if":["single-user-host","private-lock-directory","other-lock-classes"],"who_is_affected":"Exposure needs a Python application that uses StrictSoftFileLock (from 3.30.0) or SoftReadWriteLock (from 4.0.0) with lock files in a directory other local users can write to, such as a shared /tmp path on a multi-user host. Single-user machines, containers with a private lock directory, and code that uses other filelock lock classes are not affected.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.000642,"input_tokens":3381,"output_tokens":608,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-112911':13A,16A '-2026':12A,15A '3.30.0':44B,87C,93C '4.0.0':98C '4.2.1':46B,89C,132C 'admit':123C 'adopt':51B,100C 'allow':115C 'alter':69B,119C 'anoth':58B,107C 'break':5A 'concurr':74B,124C 'creat':55B,104C 'cross':38B 'cross-process':37B 'cve':11A,14A 'dev':19A 'directori':10A,54B,65B,103C,114C 'file':40B,82C 'filelock':1A,20A,21B,31B,76C 'first':56B,105C 'fix':129C 'holder':75B,125C 'host':25B 'independ':81C 'issu':127C 'let':66B,73B 'librari':35B 'local':2A,59B,108C 'lock':6A,41B,53B,70B,83C 'multi':23B 'multi-user-host':22B 'packag':26B 'parent':64B,113C 'platform':80C 'platform-independ':79C 'process':39B 'protocol':102C,120C 'python':27B,34B,85C 'share':9A,29B,63B,112C 'shared-tmp':28B 'softreadwritelock':49B,95C 'state':7A,71B,121C 'strictsoftfilelock':47B,90C 'tmp':30B 'tox':18A 'tox-dev':17A 'user':3A,24B,60B,68B,109C,117C 'version':43B,91C,96C,131C","nicknames":[],"mitigations":[],"who_affected":"Exposure needs a Python application that uses StrictSoftFileLock (from 3.30.0) or SoftReadWriteLock (from 4.0.0) with lock files in a directory other local users can write to, such as a shared /tmp path on a multi-user host. Single-user machines, containers with a private lock directory, and code that uses other filelock lock classes are not affected.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-20T15:17:15+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H","cvss_by":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-112911","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-112911","severity":null,"published_at":"2026-10-20T15:17:15+00:00","modified_at":"2026-10-21T21:21:20+00:00","first_seen_at":"2026-10-23T21:57:20+00:00","fetched_at":"2026-10-23T22:28:58+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}