CVE-2026-112909VulnerabilityPublished 29 Oct 2026

lexicon · filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path

Affects lexiconSource GCVE Database

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Authoritative record:CVE-2026-112909· Medium 6.1

Not known to be exploited · CVSS 6.1 Medium : upgrade to 3.25.2_5 when convenient.

Data as of 30 Oct 2026, 07:32 UTC

CVSS 3.1 base score

6.1Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	6.1

Patch: Available – fixed in 3.25.2_5

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade lexicon to 3.25.2_5.

Affected software

Product	Affected	Fixed in
Homebrewlexicon`pkg:brew/lexicon`Other threats	Affected >=3.11.2 <3.25.2_5	Fixed in 3.25.2_5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in filelock version 3.25.2_5. Users should upgrade to this version or later to remediate the vulnerability. The vulnerability depends on directory permissions and kernel settings; ensuring directories containing lock files have the sticky bit set and that fs.protected_hardlinks is enabled (set to 1) can reduce risk. No additional action is required once patched.

Description

UnixFileLock, used by FileLock and AsyncFileLock on Unix systems, truncates and changes permissions of any regular file that another local user renames or hard-links onto the lock path. This can lead to unintended file truncation and permission changes, allowing the other user to read and modify the file contents thereafter. The vulnerability affects all filelock releases up to and including 4.2.0, with the chmod behavior introduced since version 3.10.2. Exploitation requires local access and the ability to rename or hard-link files in certain directory conditions. The issue is patched in version 3.25.2_5.

Impact

A local attacker with low privileges can cause the lock user's file to be truncated and have its permissions changed, enabling the attacker to read and modify the file contents. This compromises the integrity of the lock user's data and potentially allows code execution if the affected file is executed or trusted by the lock user. Confidentiality impact is limited to what the lock user writes after truncation. There is no availability impact. The attack requires the attacker to control file names in non-sticky directories or have kernel settings that allow hard-link creation in sticky directories.

Summary

The UnixFileLock backend empties (truncates) any regular file found at the lock path once it acquires the flock. If an explicit mode is set, it also changes the file's permission bits regardless of whether it created the file. A local attacker who can rename or hard-link one of the lock user's files onto the lock path before the lock user's next acquire call can cause that file to be truncated and have its permissions changed. This allows the attacker to read and modify the file contents subsequently. The vulnerability depends on directory permissions and kernel settings such as the sticky bit and fs.protected_hardlinks. It affects all filelock versions up to 4.2.0, with the chmod behavior since 3.10.2. The issue is fixed in version 3.25.2_5.

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Description

AI analysisMachine-generated, updated 30 Oct 2026, 07:32 UTC

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