Firefox sandbox escape; widely deployed product; could lead to host compromise.
CVE-2026-8401
Sandbox escape in Firefox Profile Backup; patched in 150.0.3
Is CVE-2026-8401 being exploited?
Not confirmed. CVE-2026-8401 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-2026-8401?
CVE-2026-8401 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-2026-8401?
Yes. A fix has been recorded for CVE-2026-8401. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-8401 affect?
CVE-2026-8401 affects Mozilla Firefox. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-8401?
Update Firefox to 150.0.3 or newer
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Escape browser sandbox to execute arbitrary code on the OS via Profile Backup component.
Patch when possible