What is CVE-2025-23109?

CVE-2025-23109 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2025-01-11.

How severe is CVE-2025-23109?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Mozilla Firefox

CVE-2025-23109

Long hostnames in URLs could be leveraged to obscure the actual host of the website or spoof the website address. This vulnerability was fixed in Firefox for iOS 134.

Published 2025-01-11 · last modified 2026-10-05.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (7.7th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 7.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Mozilla Firefox
Mozilla Firefox For iOS — versions 134

Weakness classification (CWE)

CWE-346 — Origin Validation Error

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2025-06/ (Vendor Advisory)

Frequently asked questions

What is CVE-2025-23109?: CVE-2025-23109 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2025-01-11.
How severe is CVE-2025-23109?: Medium severity. CVSS v3 base score is 6.5 out of 10.