CVE-2026-53899

Description

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.

CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0010

Probability of exploitation

0.01%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-345 CWE-345

Affected Products

Vendor	Product	Versions
mozilla	firefox_mobile	< 152.0

References

Advisories & Patches

https://www.mozilla.org/security/advisories/mfsa2026-56/

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=2042909

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-53899? +

CVE-2026-53899 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0010, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-53899? +

CVE-2026-53899 affects products from mozilla, specifically: firefox_mobile. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-53899? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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