What’s Vulnerable › Vulnerabilities

CVE-2025-5271: Devtools' preview ignored CSP headers

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-05-27 · updated 2026-09-30
• Weakness: CWE-116

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.

Affected products

• Mozilla Firefox: before 139.0 — fixed in 139.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 139.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1920348
• https://www.mozilla.org/security/advisories/mfsa2025-42/
• https://www.mozilla.org/security/advisories/mfsa2025-45/

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