CVE-2026-74962
Site-isolation flaw in Firefox/Thunderbird allows cross-origin cookie access.
Is CVE-2026-74962 being exploited?
Not confirmed. CVE-2026-74962 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.16% probability of exploitation in the next 30 days.
How severe is CVE-2026-74962?
CVE-2026-74962 is rated High with a CVSS score of 8.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-74962?
Yes. A fix has been recorded for CVE-2026-74962. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74962 affect?
CVE-2026-74962 affects Mozilla Firefox < 154, Firefox ESR < 140.14, Firefox ESR < 153.1, Mozilla Thunderbird < 154, and 2 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74962?
Update Firefox/Thunderbird to 154 or ESR 140.14/153.1 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypass site isolation to read/modify cross-origin cookies and data via web/email content, enabling session hijack, data disclosure, or auth bypass.
Patch when possible