---
id: CVE-2025-5271
title: >-
  Previewing a response in Devtools ignored CSP headers, which could have
  allowed content injection attacks
summary: >-
  Previewing a response in Devtools ignored CSP headers, which could have
  allowed content injection attacks. This vulnerability was fixed in Firefox 139
  and Thunderbird 139.
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-116
vendor: mozilla
product: firefox
affected:
  - firefox < 139.0
patched:
  - firefox 139.0
published: '2025-05-27'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-5271'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1920348'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-42/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-45/'
    label: security@mozilla.org
tags:
  - nvd
epss: 0.00305
epssPercentile: 0.20975
ingestedAt: '2026-09-30T18:17:24.441Z'
---

## Overview

Previewing a response in Devtools ignored CSP headers, which could have allowed content injection attacks. This vulnerability was fixed in Firefox 139 and Thunderbird 139.

## Affected

- `firefox < 139.0`

## Remediation

Upgrade past the affected range:

- `firefox 139.0`