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CVE-2025-68146— filelock has TOCTOU race condition that allows symlink attacks during lock file creation

Quick assessment

Affected
tox-dev filelock
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

filelock是tox development team开源的一个Python文件锁。 filelock 3.20.1之前版本存在安全漏洞，该漏洞源于存在TOCTOU竞争条件，可能导致任意文件损坏或截断。

CVSS 6.3 · Medium EPSS 0.20% · P9
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I. Basic Information for CVE-2025-68146

Vulnerability Information
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Vulnerability Title
filelock has TOCTOU race condition that allows symlink attacks during lock file creation
Source: CVE Program / CVE List V5
Vulnerability Description
filelock is a platform-independent file lock for Python. In versions prior to 3.20.1, a Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. All users of filelock on Unix, Linux, macOS, and Windows systems are impacted. The vulnerability cascades to dependent libraries. The attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. The issue is fixed in version 3.20.1. If immediate upgrade is not possible, use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases); ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks; and/or monitor lock file directories for suspicious symlinks before running trusted applications. These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
检查时间与使用时间(TOCTOU)的竞争条件
Source: CVE Program / CVE List V5
Vulnerability Title
filelock 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
filelock是tox development team开源的一个Python文件锁。 filelock 3.20.1之前版本存在安全漏洞，该漏洞源于存在TOCTOU竞争条件，可能导致任意文件损坏或截断。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
tox-dev filelock < 3.20.1 -

II. Public POCs for CVE-2025-68146

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III. Intelligence Information for CVE-2025-68146

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Patches & Fixes for CVE-2025-68146 (2)

Vendor Advisories for CVE-2025-68146 (1)

Other References for CVE-2025-68146 (1)

IV. Related Vulnerabilities

Same product: filelock
Same vendor: tox-dev
Same weakness: CWE-367

V. Comments for CVE-2025-68146

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