CVE-2026-53899: Cross-origin cookies could be leaked when opening a PDF link

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-16 · updated 2026-10-26
Weakness: CWE-345

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.

Affected products

Mozilla Firefox for Android: before 152.0 — fixed in 152.0

How to fix

Upgrade to a fixed version: Mozilla Firefox for Android 152.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2042909
https://www.mozilla.org/security/advisories/mfsa2026-56/

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