CVE-2025-5271 — Improper Encoding or Escaping of Output in Mozilla Firefox

CWE-116 — Improper Encoding or Escaping of OutputCWE-807 — Reliance on Untrusted Inputs in a Security Decision9 documents8 sources
Severity
6.5MEDIUMNVD
EPSS
0.3%
top 48.39%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
2
Mozilla FirefoxMozilla Thunderbird
Timeline
PublishedMay 27
Latest updateFeb 2

Description

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:NExploitability: 3.9 | Impact: 2.5

Affected Packages2 packages

▶NVDmozilla/firefox< 139.0
▶Ubuntumozilla/thunderbird< 1:140.7.1+build1-0ubuntu0.22.04.1

🔴Vulnerability Details

3
CVEList
Devtools' preview ignored CSP headers↗2025-05-27
▶
GHSA
GHSA-jc7v-r8h6-xr5c: Previewing a response in Devtools ignored CSP headers, which could have allowed content injection attacks↗2025-05-27
▶
OSV
CVE-2025-5271: Previewing a response in Devtools ignored CSP headers, which could have allowed content injection attacks↗2025-05-27
▶

📋Vendor Advisories

5
Ubuntu
Thunderbird vulnerabilities↗2026-02-02
▶
Red Hat
firefox: Devtools' preview ignored CSP headers↗2025-05-27
▶
Debian
CVE-2025-5271: firefox - Previewing a response in Devtools ignored CSP headers, which could have allowed ...↗2025
▶
Mozilla
Mozilla Foundation Security Advisory 2025-42: CVE-2025-5271↗
▶
Mozilla
Mozilla Foundation Security Advisory 2025-45: CVE-2025-5271↗
▶
CVE-2025-5271 — Improper Encoding or Escaping of Output | cvebase