What is CVE-2026-84135?

CVE-2026-84135 is a critical-severity vulnerability in Mozilla Firefox Mobile, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2026-09-01.

How severe is CVE-2026-84135?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Information disclosure in Mozilla Firefox Mobile

CVE-2026-84135

Other issue in Firefox Focus for Android. This vulnerability was fixed in Firefox 155.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2026-09-01 · last modified 2026-09-03.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (37.6th percentile), scored 2026-10-17.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 38th percentile — 37.6% 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: +0.002

Affected products

Mozilla Firefox Mobile

Weakness classification (CWE)

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2026-82/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-84135?: CVE-2026-84135 is a critical-severity vulnerability in Mozilla Firefox Mobile, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2026-09-01.
How severe is CVE-2026-84135?: Critical severity. CVSS v3 base score is 9.8 out of 10.