CVE-2025-5271 Devtools' preview ignored CSP headers

What is CVE-2025-5271?

CVE-2025-5271 is a medium-severity cross-site scripting vulnerability in Mozilla Firefox, published on 27 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-116

Which versions are affected by CVE-2025-5271?

It affects 1 product.

Products include Mozilla Firefox.

How do I fix CVE-2025-5271?

Upgrade to a fixed version.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2025-5271 being exploited?

There is no known exploitation of CVE-2025-5271 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-jc7v-r8h6-xr5c, UBUNTU-CVE-2025-5271.