How severe is CVE-2026-53899?

CVE-2026-53899 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-53899 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-53899?

CVE-2026-53899 affects Mozilla Firefox Mobile. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-53899?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-53899 have an EU (EUVD) identifier?

Yes. CVE-2026-53899 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37077.

When was CVE-2026-53899 published?

CVE-2026-53899 was published on 2026-06-16 and last updated on 2026-06-17.

CVE-2026-53899

CVE-2026-53899 is a medium-severity vulnerability in Mozilla Firefox Mobile with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (1st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37077
Weakness: CWE-345
Affected product: Mozilla Firefox Mobile
Published: 2026-06-16
Last modified: 2026-06-17

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.

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.
How severe is CVE-2026-53899?: CVE-2026-53899 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-53899 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-53899?: CVE-2026-53899 affects Mozilla Firefox Mobile. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-53899?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-53899 have an EU (EUVD) identifier?: Yes. CVE-2026-53899 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37077.
When was CVE-2026-53899 published?: CVE-2026-53899 was published on 2026-06-16 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mozilla:firefox_mobile:*:*:*:*:*:iphone_os:*:*

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