What’s Vulnerable › Vulnerabilities

CVE-2026-74962: Site isolation issue in the Networking: Cookies component

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-18 · updated 2026-08-19
• Weakness: CWE-346

Description

Site isolation issue in the Networking: Cookies component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

Affected products

• Mozilla Firefox: before 140.14.0; from 141.0.0 before 153.1.0 — fixed in 140.14.0, 153.1.0
• Mozilla Thunderbird: before 140.14.0; from 141.0 before 153.1.0 — fixed in 140.14.0, 153.1.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.14.0, 153.1.0; Mozilla Thunderbird 140.14.0, 153.1.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2050425
• https://www.mozilla.org/security/advisories/mfsa2026-74/
• https://www.mozilla.org/security/advisories/mfsa2026-76/
• https://www.mozilla.org/security/advisories/mfsa2026-77/
• https://www.mozilla.org/security/advisories/mfsa2026-78/
• https://www.mozilla.org/security/advisories/mfsa2026-79/
• https://www.mozilla.org/security/advisories/mfsa2026-80/

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