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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].

Sources and references

Verified primary and authoritative sources

  • CVE-2026-53899 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-53899

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-53899 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-53899

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.