What is CVE-2026-0881?

CVE-2026-0881 is a critical-severity vulnerability in Mozilla Firefox, classified under Improper Access Control. CVSS score: 10.0/10. Published 2026-01-13.

How severe is CVE-2026-0881?

Critical severity. CVSS v3 base score is 10.0 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-0881

Sandbox escape in the Messaging System component. This vulnerability was fixed in Firefox 147 and Thunderbird 147.

Published 2026-01-13 · last modified 2026-07-15.

CVSS v3 metric

CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (26.9th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.000

Affected products

Mozilla Firefox — versions 147
Mozilla Thunderbird — versions 147

Weakness classification (CWE)

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-01/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-04/ (Vendor Advisory)
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Frequently asked questions

What is CVE-2026-0881?: CVE-2026-0881 is a critical-severity vulnerability in Mozilla Firefox, classified under Improper Access Control. CVSS score: 10.0/10. Published 2026-01-13.
How severe is CVE-2026-0881?: Critical severity. CVSS v3 base score is 10.0 out of 10.