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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 Mozilla Suse Red Hat
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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
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. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Lure victim to malicious content
Exploit
Craft request abusing networking flaw
Execution
Bypass network security mitigation
Impact
Read or tamper with protected data
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Vulnerability AssessmentAI

Exploitation The affected code path is Firefox's Networking component and the bug is a mitigation/protection-mechanism bypass (CWE-693), so exploitation requires that the specific network-layer defense being circumvented is engaged in the victim's session - the terse description does not name the exact feature (e.g., connection partitioning, origin isolation, or an auth-related network control). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N, score 9.1) presents this as network-reachable, low-complexity, unauthenticated, with high confidentiality and integrity impact and no availability impact - consistent with a protection-mechanism bypass that leaks or tampers with data rather than crashing the browser. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker hosts a malicious web page or holds a privileged network position and crafts traffic that causes Firefox's networking layer to skip or bypass a security mitigation, allowing the attacker to read sensitive data or tamper with request/response integrity across a trust boundary that should have been enforced. Given the low attack complexity, once the specific bypass technique is known it could be reliably reproduced; however, no public exploit identified at time of analysis.
Remediation 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/). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, inventory all Mozilla Firefox installations organization-wide and identify systems running versions prior to 153; establish direct communication with Mozilla security advisors regarding MFSA2026-68 patch timeline and confirm remediation schedule. …

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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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