PatchSiren cyber security CVE debrief
CVE-2026-53899 Mozilla CVE debrief
CVE-2026-53899 is a vulnerability in Firefox for iOS that allows a malicious site on a suffix domain to receive cookies belonging to the target site due to partial domain matching when attaching cookies to PDF requests. This issue was fixed in Firefox for iOS 152.0. The vulnerability was published on [cvePublishedAt] and has not been associated with a CVSS score or severity level.
- Vendor
- Mozilla
- Product
- Firefox for iOS
- CVSS
- MEDIUM 6.5
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-06-16
- Original CVE updated
- 2026-06-17
- Advisory published
- 2026-06-16
- Advisory updated
- 2026-06-17
Who should care
Users of Firefox for iOS, particularly those visiting sites on suffix domains, should be aware of this vulnerability. Developers and administrators should ensure that users update to Firefox for iOS 152.0 or later.
Technical summary
The vulnerability arises from the browser's partial domain matching behavior when attaching cookies to PDF requests. This allows a malicious site on a suffix domain to potentially intercept cookies intended for a different site.
Defensive priority
High
Recommended defensive actions
- Update Firefox for iOS to version 152.0 or later.
- Be cautious when visiting sites on suffix domains, especially if they are similar to legitimate sites.
Evidence notes
The CVE record was obtained from [resourceLinkAnnotations:cve-org]. Additional details were found in the NVD entry [resourceLinkAnnotations:nvd] and Mozilla's security advisories [resourceLinkAnnotations:ref-5].
Official resources
CVE-2026-53899 was published and modified on 2026-06-16T13:16:37.420Z.