Is CVE-2026-12304 in the CISA KEV catalog?

No. CVE-2026-12304 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-12304?

CVE-2026-12304 has a CVSS v3 base score of 9.1 (CRITICAL).

What is the EPSS score for CVE-2026-12304?

CVE-2026-12304 has an EPSS score of 0.19% (9th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-12304?

Upgrade firefox on debian unstable to 152.0-1 or later. Fixes are available for 18 affected products.

CVE & CISA-KEV Catalog

CVE-2026-12304

CRITICAL

9.1

CVSS v3

NVD

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.

CWE-346

How to fix

Remediation Available

firefoxDebian

Fixed in:152.0-1CVE-2026-12304

firefoxRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefoxRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-debuginfoRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-debuginfoRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-debugsourceRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-debugsourceRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:27733

Fixed in:0:140.12.0-1.el8_10RHSA-2026:27717

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-x11Rocky

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

firefox-x11Red Hat / RHEL

Fixed in:0:140.12.0-1.el9_8RHSA-2026:27734

thunderbirdRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

thunderbirdRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

thunderbird-debuginfoRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

thunderbird-debuginfoRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

thunderbird-debugsourceRocky

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

thunderbird-debugsourceRed Hat / RHEL

Fixed in:0:140.12.0-1.el10_2RHSA-2026:30846

Fixed in:0:140.12.0-1.el8_10RHSA-2026:33445

Fixed in:0:140.12.0-1.el9_8RHSA-2026:29940

DeveloperEditionWindows application

Affected:152.0.0Fixed in:152.0.0Mozilla

Affected:140.12.0Fixed in:140.12.0Mozilla

Mozilla Firefox (en-US)Windows application

Affected:152.0.0Fixed in:152.0.0Mozilla

Affected:140.12.0Fixed in:140.12.0Mozilla

Mozilla Thunderbird (en-US)Windows application

Affected:140.12.0Fixed in:140.12.0Mozilla

Affected:152.0.0Fixed in:152.0.0Mozilla

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploit Intelligence

0.19%probability of exploitation in 30 days

9thpercentile

Low risk: more likely to be exploited than 9% of all known CVEs.

References

Vendor Advisory4

Other references1

bugzilla.mozilla.org

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.