Bug 2567560 (CVE-2026-112910)

Summary: CVE-2026-112910 filelock: filelock: Denial of Service via improper lock file permissions on Windows
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in filelock. On Windows platforms, the library ignores requested file mode permissions when creating lock files and database files, causing them to inherit default permissions from the parent directory's access control list (ACL). A local user on the same system can exploit this flaw to cause a Denial of Service (DoS) by taking the lock and blocking legitimate processes, read lock metadata, or modify lock state if write permissions are inherited.
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Description OSIDB Bzimport 2026-11-05 22:07:33 UTC 
filelock is a platform-independent file lock for Python. From 3.10.0 until 4.2.1, filelock on Windows ignores the mode argument for WindowsFileLock files and the ReadWriteLock SQLite database. A lock created with mode=0o600 receives the parent directory's inheritable ACL because _open_non_reparse_fd and _nt_open do not create an owner-only security descriptor. Another local account with inherited access can read holder metadata or the lock database, modify those files where the ACL permits writes, or take the byte-range lock after release and delay later acquisitions. UnixFileLock is not affected, and mutual exclusion between cooperating processes continues to hold. This issue is fixed in version 4.2.1.