CVE-2025-6427 connect-src Content Security Policy restriction could be bypassed

What is CVE-2025-6427?

CVE-2025-6427 is a critical vulnerability in Mozilla Firefox, published on 24 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Weakness: CWE-693

Which versions are affected by CVE-2025-6427?

It affects 1 product.

Products include Mozilla Firefox.

How do I fix CVE-2025-6427?

Upgrade to a fixed version.

Is CVE-2025-6427 being exploited?

There is no known exploitation of CVE-2025-6427 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-823q-pcrj-c4xv, UBUNTU-CVE-2025-6427.