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Mozilla Firefox CVE-2026-16380

| EUVDEUVD-2026-46217 CRITICAL
Protection Mechanism Failure (CWE-693)
2026-07-21 mozilla GHSA-fhc2-c9vh-xrg3
Authentication Bypass Red Hat Mozilla
Critical
Disputed · 9.1 Vendor: mozilla
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Severity by source

Sources disagree (Medium–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
6.8 MEDIUM

Browser mitigation bypass realistically needs a victim to visit attacker content (UI:R) and depends on network/second-bug conditions (AC:H), while remaining unauthenticated with high C/I and no availability impact.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
4.0 AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
CRITICAL
qualitative
Red Hat
6.1 MEDIUM
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 22, 2026 - 19:39 vuln.today
CVSS changed
Jul 22, 2026 - 18:22 NVD
9.1 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:37 cve.org
CRITICAL 9.1
CVE Published
Jul 21, 2026 - 12:37 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

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

AnalysisAI

Protection mechanism bypass in the Networking component of Mozilla Firefox (versions prior to 153) allows remote attackers to circumvent a built-in security mitigation over the network without authentication or user interaction, per the CVSS vector (AV:N/AC:L/PR:N/UI:N). Mozilla (MFSA2026-68) tags this as an authentication/mitigation bypass with high confidentiality and integrity impact but no availability impact. No public exploit identified at time of analysis, and EPSS exploitation probability is low at 0.15% (5th percentile).

Technical ContextAI

The flaw resides in Firefox's Networking component, which handles HTTP(S) connections, protocol parsing, origin/security-boundary enforcement, and transport-layer protections. It is classified under CWE-693 (Protection Mechanism Failure), meaning an existing security control - likely a network-facing safeguard such as an origin, transport, or authentication/isolation check - can be bypassed rather than a memory-safety defect. The affected CPE is cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*, covering the Firefox desktop browser application across versions before the fixed 153 release. Because it is a mitigation bypass rather than a direct memory-corruption bug, exploitation typically requires chaining this weakness with a malicious server or crafted network response to defeat the intended protection.

RemediationAI

Vendor-released patch: Firefox 153 - upgrade all Firefox desktop installations to version 153 or later, which is the primary and complete fix per Mozilla advisory MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/). Because this is a browser-side networking mitigation bypass with no documented standalone workaround, the practical compensating controls until patching are to enforce Firefox auto-update, restrict browsing to trusted sites, and route traffic through an inspecting proxy or DNS/URL filtering to reduce exposure to malicious servers that could trigger the bypass; these controls reduce but do not eliminate risk and add management overhead and potential HTTPS-inspection privacy trade-offs. Enterprises managing Firefox via policy should push the update through their software distribution channel and verify the running version. Reference the Bugzilla tracker (https://bugzilla.mozilla.org/show_bug.cgi?id=2040386) for technical follow-up.

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Same weakness CWE-693 – Protection Mechanism Failure

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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-2026-16380 vulnerability details – vuln.today
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