---
id: CVE-2025-12972
title: >-
  Fluent Bit out_file plugin does not properly sanitize tag values when deriving
  output file names
summary: >-
  Fluent Bit out_file plugin does not properly sanitize tag values when deriving
  output file names. When the File option is omitted, the plugin uses untrusted
  tag input to construct file paths. This allows attackers with network access
  to …
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-22
vendor: treasuredata
product: fluent_bit
affected:
  - fluent_bit = 4.1.0
published: '2025-11-24'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T10:10:00.227'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-12972'
references:
  - url: >-
      https://fluentbit.io/blog/2025/10/28/security-vulnerabilities-addressed-in-fluent-bit-v4.1-and-backported-to-v4.0/
    label: cret@cert.org
  - url: >-
      https://www.oligo.security/blog/critical-vulnerabilities-in-fluent-bit-expose-cloud-environments-to-remote-takeover
    label: cret@cert.org
tags:
  - nvd
epss: 0.00898
epssPercentile: 0.58354
ingestedAt: '2026-10-08T10:28:22.457Z'
---

## Overview

Fluent Bit out_file plugin does not properly sanitize tag values when deriving output file names. When the File option is omitted, the plugin uses untrusted tag input to construct file paths. This allows attackers with network access to craft tags containing path traversal sequences that cause Fluent Bit to write files outside the intended output directory.

## Affected

- `fluent_bit = 4.1.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.