Description
Setting a nameless cookie with an equals sign in the value shadowed other cookies. Even if the nameless cookie was set over HTTP and the shadowed cookie included the `Secure` attribute. This vulnerability was fixed in Firefox 141, Firefox ESR 140.1, Thunderbird 141, and Thunderbird 140.1.
Affected products
mozilla: firefox; mozilla: thunderbird
References5
- www.mozilla.org/security/advisories/mfsa2025-56/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-59/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-61/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-63/ Vendor Advisory
- bugzilla.mozilla.org/show_bug.cgi?id=1964767 Permissions Required
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 0% percentile: 19 · as of 8 November 2026
- CWE
- CWE-614
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.