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Mozilla Firefox CVE-2026-16349

| EUVDEUVD-2026-46189 CRITICAL
Origin Validation Error (CWE-346)
2026-07-21 mozilla GHSA-9cw3-v4hh-fhf9
Authentication Bypass Red Hat Mozilla
9.8
CVSS 3.1 · Vendor: mozilla
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Severity by source

Vendor (mozilla) PRIMARY
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
9.3 CRITICAL

A browser SOP bypass needs the victim to load attacker content (UI:R) and crosses the origin trust boundary (S:C); high confidentiality/integrity but no genuine availability impact (A:N).

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:L/SA:N
SUSE
CRITICAL
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
Analysis Generated
Jul 22, 2026 - 17:17 vuln.today
CVSS changed
Jul 22, 2026 - 16:22 NVD
9.8 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:37 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 21, 2026 - 12:37 cve.org
CRITICAL 9.8

DescriptionCVE.org

Same-origin policy bypass in the DOM: Navigation component. This vulnerability was fixed in Firefox 153, Firefox ESR 115.38, and Firefox ESR 140.13.

AnalysisAI

Same-origin policy bypass in Mozilla Firefox's DOM: Navigation component allows a malicious web page to read or manipulate content belonging to another origin, defeating the browser's core cross-origin isolation boundary. All Firefox users on affected pre-153 releases and unpatched ESR branches are exposed, and while Mozilla's vector maps to CVSS 9.8, EPSS estimates only a 0.16% exploitation probability (6th percentile). There is no public exploit identified at time of analysis and it is not in CISA KEV.

Technical ContextAI

The flaw sits in Firefox's DOM Navigation handling, the Gecko subsystem responsible for enforcing the Same-Origin Policy (SOP) as documents navigate, redirect, and pass references between browsing contexts. The root cause is CWE-346 (Origin Validation Error): the component fails to correctly validate or attribute the security origin during a navigation transition, so a document from origin A gains access it should only have over origin B. The affected CPE (cpe:2.3:a:mozilla:firefox:*) identifies the desktop/ESR browser engine rather than a plugin or extension. Mozilla tags this as an Authentication Bypass because breaking SOP effectively lets attacker script reach the authenticated session context of an unrelated site (cookies, DOM, credentialed responses).

RemediationAI

Vendor-released patch: upgrade to Firefox 153 on the mainline channel, Firefox ESR 115.38 on the 115 branch, or Firefox ESR 140.13 on the 140 branch, per Mozilla advisories mfsa2026-68/69/70 (https://www.mozilla.org/security/advisories/mfsa2026-68/, /mfsa2026-69/, /mfsa2026-70/). Because Firefox auto-updates by default, ensure automatic updates are enabled and restart the browser to apply the new build; in managed fleets push the updated MSI/PKG or set update policy so ESR clients pull 115.38/140.13. There is no reliable configuration-only workaround for a same-origin policy engine flaw, so patching is the only complete fix; as an interim compensating control for high-risk users, restrict browsing to trusted sites or isolate Firefox in a sandboxed/VDI profile to reduce exposure to malicious pages, accepting the usability trade-off that this limits general web use.

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Same weakness CWE-346 – Origin Validation Error

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Same technique Authentication Bypass

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CVE-2023-46805 HIGH POC
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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected

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CVE-2026-16349 vulnerability details – vuln.today
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