CVE-2026-74979
Add‑ons Manager mitigation bypass in Firefox/Thunderbird allows silent malicious extension install.
Is CVE-2026-74979 being exploited?
Not confirmed. CVE-2026-74979 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 0.31% probability of exploitation in the next 30 days.
How severe is CVE-2026-74979?
CVE-2026-74979 is rated Critical with a CVSS score of 9.8. 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-2026-74979?
Yes. A fix has been recorded for CVE-2026-74979. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74979 affect?
CVE-2026-74979 affects Firefox < 154, Firefox ESR < 153.1, Thunderbird < 154, Thunderbird ESR < 153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74979?
Update to Firefox 154 / ESR 153.1 and Thunderbird 154 / ESR 153.1 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypass permits silent install/enable of malicious add-ons, enabling remote code execution, persistent compromise, and data exfiltration.
Immediate action required