Review reviewCritical

CVE-2026-12304

Mozilla Firefox, Thunderbird, firefox

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.

CVSS
9.1
EPSS
0.19%
8.82% percentile
CISA KEV
Not listed
Published
2026.06.16
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.19%
Technical severityCVSS 9.1

Vulnerability overview

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.

Affected product and versions

Product
Mozilla Firefox, Thunderbird, firefox
Affected versions
< 140.12.0, < 152.0.0
Fixed versions
140.12.0, 152.0.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Mozilla Firefox, Thunderbird, firefox and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CWE
CWE-346
CVE-2026-12304 — Mozilla Firefox, Thunderbird, firefox | SECUFOCUS NOW