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VulnerabilityPublished

CVE-2026-12304: Mozilla Firefox · CWE-346

Affects Mozilla FirefoxSource CVE Database V5

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Not known to be exploited · CVSS 9.1 Critical · patch available : patch Mozilla Firefox as a priority.

Data as of 30 Oct 2026, 20:25 UTC

CVSS 3.1 base score
9.1Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
Mozilla FirefoxAffected
  • <152
  • <140.12
Fixed in
  • 152
  • 140.12

AI-suggested

This vulnerability has been fixed in Mozilla Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12. Users and administrators should update affected products to these versions or later to remediate the issue. Mozilla manages the patching process for these products and has published official advisories detailing the fixes. Patch status is confirmed by the vendor advisories. No additional mitigations beyond applying the official updates are indicated.

Description

CVE-2026-12304 is a same-origin policy bypass vulnerability in the Networking: Cookies component of Mozilla Firefox and Thunderbird. This vulnerability allows bypassing the same-origin policy, which is a fundamental security mechanism in web browsers. The issue was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12. The vulnerability has a critical CVSS score of 9.1. Mozilla has published official security advisories confirming the fix and providing detailed information about this and other related vulnerabilities.

References

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