CVE-2026-112909VulnerabilityPublished 29 Oct 2026

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

Affects poetrySource 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 2.5.1_1 or 1.6.1_1 when convenient.

Data as of 30 Oct 2026, 08:30 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 2.5.1_1, 1.6.1_1

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 poetry to 2.5.1_1 or 1.6.1_1.

Affected software

Product	Affected	Fixed in
Homebrewpoetry`pkg:brew/poetry`Other threats	Affected >=1.1.0 <1.6.1_1 >=1.8.0 <2.5.1_1	Fixed in 1.6.1_1 2.5.1_1

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

AI-suggested

A patch is available and should be applied by upgrading filelock to versions 1.6.1_1 or 2.5.1_1 or later. The vulnerability is conditional on directory permissions and kernel settings; ensuring lock directories have the sticky bit set and that fs.protected_hardlinks is enabled (set to 1) can mitigate the risk. No additional action is required once the patch is applied.

Description

UnixFileLock, used by FileLock and AsyncFileLock on Unix systems, truncates and can change permissions of any regular file that another local user renames or hard-links onto the lock path before the lock is acquired. This allows a local attacker with write access to certain directories to cause the lock user to truncate and potentially expose files to unauthorized read/write access. The vulnerability affects all filelock releases up to and including 4.2.0 and requires specific conditions such as writable non-sticky directories or disabled kernel hardlink protections. The CVSS 3.1 score is 6.1 (Medium).

Impact

A local attacker with low privileges can cause the lock user's process to truncate arbitrary files by renaming or hard-linking them onto the lock path before the lock is acquired. If the lock is acquired with an explicit mode (e.g., 0o666), the attacker can also gain read and write access to the file, potentially leading to unauthorized modification of the lock user's data or code execution if the file is later executed or trusted. Confidentiality impact is limited to what the lock user writes after the truncation, and availability is not affected. The attack requires specific filesystem and directory permissions conditions to be exploitable.

Summary

The UnixFileLock backend truncates any regular file it finds at the lock path once it acquires the flock, and if an explicit mode is set, it also changes the file's permissions regardless of whether it created the file. A local user can exploit this by renaming or hard-linking one of the lock user's files onto the lock path before the lock is acquired, causing that file to be truncated and potentially made readable and writable by the attacker if a permissive mode is applied. The attack requires the attacker to have write permissions in a directory without the sticky bit or a system with fs.protected_hardlinks=0. This vulnerability affects all filelock versions up to 4.2.0, with truncation present since the project's inception and chmod behavior since version 3.10.2. The vulnerability is rated medium severity with CVSS 3.1 vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N. Fixes are available in filelock versions 1.6.1_1 and 2.5.1_1.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:30 UTC

Technical details

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