CVE-2026-112915 in filelock
Summary
by MITRE • 10/20/2026
filelock is a platform-independent file lock for Python. From 3.20.4 until 4.2.1, ReadWriteLock can open a crafted SQLite lock database without bounding schema and query work, allowing another local user who can replace the database to make acquisition stall or hang; versions from 3.20.4 expose this on initial per-instance opening, and versions from 3.30.0 repeat the exposure on every acquisition. This issue is fixed in version 4.2.1.
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Analysis
by VulDB Data Team • 10/20/2026
The filelock library for Python provides platform-independent mechanisms to manage exclusive access to files through locking primitives. A significant security vulnerability exists within the ReadWriteLock implementation, specifically affecting versions ranging from 3.20.4 up to and including 4.2.1. This flaw stems from an insufficient validation of input data when interacting with SQLite-based lock databases. The core technical deficiency lies in the library's failure to enforce a predefined schema or bound query parameters for the underlying database structure. By allowing the creation or use of a crafted SQLite lock database without verifying its integrity against expected standards, the application inadvertently trusts external inputs that can be manipulated by local actors. This lack of strict schema enforcement creates an opening for attackers who possess write access to the target directory where the lock file resides.
The operational impact of this vulnerability centers on the potential for denial-of-service conditions through resource exhaustion or logic manipulation. An attacker with local privileges and the ability to replace or modify the SQLite database used by filelock can engineer a scenario that causes the acquisition of the lock to stall indefinitely. This hang occurs because the crafted database contains structures or queries that exploit ambiguities in how the library processes locking requests without proper validation. In versions starting from 3.20.4, this vulnerability is triggered during the initial per-instance opening of the lock mechanism. However, a more severe exposure was introduced in version 3.30.0 and persists through 4.2.1, where the flaw manifests on every subsequent acquisition attempt rather than just at initialization. This means that any process relying on filelock for synchronization can be disrupted repeatedly by an attacker who controls the lock database file, leading to application hangs or failures in critical workflows dependent on exclusive access guarantees.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-754: Improper Check for Unusual or Exceptional Conditions within the context of resource management. The attack vector is categorized under Local Privilege Escalation scenarios where an attacker leverages file system permissions to interfere with application logic. In terms of MITRE ATT&CK, this behavior corresponds to techniques involving Resource Hijacking and Denial of Service via logical exploitation rather than brute force or network flooding. The vulnerability highlights the risks associated with using dynamic database structures for critical synchronization primitives without rigorous schema validation, a common pitfall in libraries that abstract complex system interactions into simple API calls.
To mitigate this risk, organizations must upgrade to version 4.2.1 of filelock immediately, as it contains the necessary patches to enforce strict schema and query bounds on SQLite lock databases. For environments where upgrading is not immediately feasible, operational mitigations include restricting write permissions on directories containing lock files so that only the intended application process can create or modify them. Additionally, implementing integrity checks such as checksums for critical configuration and state files can help detect unauthorized modifications before they are processed by the locking mechanism. Developers should also review any custom implementations of file locks to ensure that database schemas are explicitly defined and validated against known safe structures rather than relying on implicit assumptions about data format.