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Mozilla Firefox CVE-2026-16406

| EUVDEUVD-2026-46244 CRITICAL
Protection Mechanism Failure (CWE-693)
2026-07-21 mozilla GHSA-ff33-vw52-c9p4
Authentication Bypass Red Hat Mozilla Suse
Critical
Disputed · 9.1 Vendor: mozilla
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Severity by source

Sources disagree (Low–Critical)
Vendor (mozilla) PRIMARY
9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
vuln.today AI
8.1 HIGH

Network-reachable low-complexity bypass with high confidentiality/integrity impact, but as a browser flaw it realistically needs the victim to load attacker content, so UI:R rather than the vendor's UI:N.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/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:N/SI:N/SA:N
SUSE
CRITICAL
qualitative
Red Hat
3.4 LOW
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: mozilla

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

Lifecycle Timeline

4
Analysis Generated
Jul 21, 2026 - 20:24 vuln.today
CVSS changed
Jul 21, 2026 - 20:22 NVD
9.1 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:38 cve.org
UNKNOWN (no severity yet)
CVE Published
Jul 21, 2026 - 12:38 cve.org
CRITICAL 9.1

DescriptionCVE.org

Mitigation bypass in the Networking component. This vulnerability was fixed in Firefox 153.

Articles & Coverage 1

News Critical Security Mitigation Bypass in Mozilla Firefox before 153 - CVE-2026-16406 Jul 22, 2026

AnalysisAI

Security mitigation bypass in the Networking component of Mozilla Firefox before version 153 lets remote attackers defeat a built-in protection mechanism, carrying high confidentiality and integrity impact per the CVSS 9.1 rating. The flaw was reported and fixed by Mozilla in Firefox 153 (advisory MFSA2026-68) and is classified under CWE-693 (Protection Mechanism Failure), with tags indicating an authentication/authorization bypass. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV.

Technical ContextAI

The vulnerability resides in Firefox's Networking component, which governs how the browser handles connections, request/response processing, and enforcement of network-layer security boundaries such as origin isolation, connection partitioning, CORS/same-origin controls, or transport protections. CWE-693 (Protection Mechanism Failure) indicates the root cause is not memory corruption but a defense that can be circumvented - a designed safeguard fails to be applied or can be sidestepped under specific conditions. The affected CPE is cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* (all versions prior to the fix), and Mozilla's 'Authentication Bypass' tag suggests the bypassed mitigation relates to an access-control or trust boundary within networking rather than a crash-based defect.

RemediationAI

Vendor-released patch: Firefox 153 - upgrade all Firefox installations to version 153 or later, which resolves the networking mitigation bypass per Mozilla advisory MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/). Firefox's built-in auto-update mechanism will deliver this for most users; enterprises using managed deployments or ESR channels should confirm the corresponding fixed build with Mozilla and push the update via their management tooling. No specific vendor workaround was published in the provided data, so as an interim compensating control restrict users from browsing untrusted sites and consider network egress filtering or a web proxy to limit exposure to attacker-controlled content, accepting the usability trade-off that such restrictions may block legitimate destinations. Refer to the tracking bug https://bugzilla.mozilla.org/show_bug.cgi?id=2040382 for technical detail.

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Same weakness CWE-693 – Protection Mechanism Failure

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9.8
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Same technique Authentication Bypass

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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected

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CVE-2026-16406 vulnerability details – vuln.today
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