What is CVE-2025-54143?

CVE-2025-54143 is a critical-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 9.8/10. Published 2025-08-19.

How severe is CVE-2025-54143?

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

Vulnerability in Mozilla Firefox

CVE-2025-54143

Sandboxed iframes on webpages could potentially allow downloads to the device, bypassing the expected sandbox restrictions declared on the parent page. This vulnerability was fixed in Firefox for iOS 141.

Published 2025-08-19 · last modified 2026-10-05.

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 (40.1th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 40.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Mozilla Firefox
Mozilla Firefox For iOS — versions 141

Weakness classification (CWE)

CWE-693 — Protection Mechanism Failure

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2025-60/ (Vendor Advisory)

Frequently asked questions

What is CVE-2025-54143?: CVE-2025-54143 is a critical-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 9.8/10. Published 2025-08-19.
How severe is CVE-2025-54143?: Critical severity. CVSS v3 base score is 9.8 out of 10.