How severe is CVE-2026-12304?

CVE-2026-12304 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-12304 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-12304?

CVE-2026-12304 primarily affects Mozilla Firefox. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-12304?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-12304 have an EU (EUVD) identifier?

Yes. CVE-2026-12304 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37095.

When was CVE-2026-12304 published?

CVE-2026-12304 was published on 2026-06-16 and last updated on 2026-06-17.

CVE-2026-12304

CVE-2026-12304 is a critical-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 9.1. 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-346.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (9th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37095
Weakness: CWE-346
Affected product: Mozilla Firefox
Published: 2026-06-16
Last modified: 2026-06-17

Description

Same-origin policy bypass in the Networking: Cookies component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

Frequently asked questions

What is CVE-2026-12304?: Same-origin policy bypass in the Networking: Cookies component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.
How severe is CVE-2026-12304?: CVE-2026-12304 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-12304 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-12304?: CVE-2026-12304 primarily affects Mozilla Firefox. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-12304?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-12304 have an EU (EUVD) identifier?: Yes. CVE-2026-12304 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37095.
When was CVE-2026-12304 published?: CVE-2026-12304 was published on 2026-06-16 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

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