Cyber Resilience

CVE-2026-12304

Critical

Published: 16 June 2026

Published
16 June 2026
Modified
17 June 2026
KEV Added
—
Patch
—
CVSS Score v3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS Score 0.0019 8.8th percentile
Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-12304 is a critical-severity Origin Validation Error (CWE-346) vulnerability in Mozilla Firefox. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Steal Web Session Cookie (T1539); ranked at the 8.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability details

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(s)
CWE-346

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1539 Steal Web Session Cookie Credential Access
An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials.
attack.mitre.org →
Why these techniques?

SOP bypass in cookie handling directly enables theft of web session cookies across origins.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

Affected Assets

mozilla
firefox
≤ 140.12.0 · ≤ 152.0.0
mozilla
thunderbird
≤ 140.12.0 · ≤ 152.0.0

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

IA-9 Service Identification and Authentication
addresses: CWE-346

Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.

SC-11 Trusted Path
addresses: CWE-346

Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.

SC-20 Secure Name/Address Resolution Service (Authoritative Source)
addresses: CWE-346

Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.

SC-21 Secure Name/Address Resolution Service (Recursive or Caching Resolver)
addresses: CWE-346

Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.

SC-23 Session Authenticity
addresses: CWE-346

Mandates origin validation so that only legitimate endpoints can continue the authenticated session.

References