What is CVE-2026-2634?

CVE-2026-2634 is a critical-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 9.8/10. Published 2026-02-24.

How severe is CVE-2026-2634?

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

Vulnerability in Mozilla Firefox

CVE-2026-2634

Malicious scripts could cause desynchronization between the address bar and web content before a response is received in Firefox iOS, allowing attacker-controlled pages to be presented under spoofed domains. This vulnerability was fixed in Firefox for iOS 147.4.

Published 2026-02-24 · last modified 2026-06-17.

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: 0.005 (39.9th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 39.9% 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: 0.005 · change: +0.002

Affected products

Mozilla Firefox
Mozilla Firefox For iOS — versions 147.4

Weakness classification (CWE)

CWE-451 — User Interface (UI) Misrepresentation of Critical Information

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2026-12/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-2634?: CVE-2026-2634 is a critical-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 9.8/10. Published 2026-02-24.
How severe is CVE-2026-2634?: Critical severity. CVSS v3 base score is 9.8 out of 10.