What is CVE-2026-53899?

CVE-2026-53899 is a medium-severity vulnerability in Mozilla Firefox For Ios, classified under Insufficient Verification of Data Authenticity. CVSS score: 6.5/10. Published 2026-06-16.

How severe is CVE-2026-53899?

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

Vulnerability in Mozilla Firefox For Ios

CVE-2026-53899

Firefox for iOS used partial domain matching when attaching cookies to PDF requests, allowing a malicious site on a suffix domain to receive cookies belonging to the target site. This vulnerability was fixed in Firefox for iOS 152.0.

EPSS: 0.001 (0.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

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

Affected products

Mozilla Firefox For Ios — versions 152.0
Mozilla Firefox_mobile

Weakness classification (CWE)

CWE-345 — Insufficient Verification of Data Authenticity

References

security@mozilla.org (Permissions Required)
security@mozilla.org (Vendor Advisory)

Frequently asked questions

What is CVE-2026-53899?: CVE-2026-53899 is a medium-severity vulnerability in Mozilla Firefox For Ios, classified under Insufficient Verification of Data Authenticity. CVSS score: 6.5/10. Published 2026-06-16.
How severe is CVE-2026-53899?: Medium severity. CVSS v3 base score is 6.5 out of 10.