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Mozilla Firefox CVE-2026-16407

| EUVDEUVD-2026-46245 CRITICAL
Improper Access Control (CWE-284)
2026-07-21 mozilla GHSA-x563-34jc-9396
Authentication Bypass Red Hat Mozilla
Critical
Disputed · 9.8 Vendor: mozilla
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Severity by source

Sources disagree (Low–Critical)
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
7.1 HIGH

Client-side browser flaw needs the victim to load malicious web content (UI:R); an origin/scope access-control bypass primarily threatens confidentiality (C:H) with limited integrity and no availability impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:L/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
High

Lifecycle Timeline

4
Analysis Generated
Jul 22, 2026 - 21:11 vuln.today
CVSS changed
Jul 22, 2026 - 19:22 NVD
9.8 (CRITICAL)
CVE Published
Jul 21, 2026 - 12:38 cve.org
CRITICAL 9.8
CVE Published
Jul 21, 2026 - 12:38 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

Mitigation bypass in the DOM: Service Workers component. This vulnerability was fixed in Firefox 153.

AnalysisAI

Access-control mitigation bypass in the DOM Service Workers component of Mozilla Firefox before version 153 allows remote content to circumvent a browser security mitigation, undermining protections intended to isolate web origins. Mozilla self-reported the flaw (MFSA2026-68/71) and shipped a fix in Firefox 153; there is no public exploit identified at time of analysis and EPSS is low (0.14%, 4th percentile). The NVD-assigned CVSS of 9.8 (full CIA impact, no user interaction) is notably higher than typical for a browser mitigation bypass, which warrants scrutiny.

Technical ContextAI

The affected component is the Service Workers subsystem of Firefox's DOM implementation. Service Workers are background scripts that intercept and proxy network requests for a given origin/scope, enabling offline caching, push, and fetch interception; because they sit between a web page and the network, the platform enforces strict origin, scope, and secure-context restrictions on their registration and control. The flaw is classed as CWE-284 (Improper Access Control) and tagged as an authentication/authorization bypass, indicating that one of these mitigations enforcing origin or scope boundaries could be circumvented. The single affected CPE is cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* (Firefox, all versions prior to the 153 fix). Mozilla frequently assigns 'mitigation bypass' to defects that weaken a defense-in-depth control rather than directly achieving code execution, so the practical impact depends on what secondary attack the bypass unlocks.

RemediationAI

Vendor-released patch: Firefox 153 - upgrade all Firefox installations to version 153 or later, which is the definitive fix. Because Firefox auto-updates by default, most endpoints will remediate automatically once the update is fetched; in managed environments, push the update via your software distribution/policy channels and verify the deployed build is >= 153. Consult MFSA2026-68 (https://www.mozilla.org/security/advisories/mfsa2026-68/) and MFSA2026-71 (https://www.mozilla.org/security/advisories/mfsa2026-71/) to confirm the corresponding fixed build for any ESR or extended-support channel you run. No standalone workaround is documented; as an interim compensating control you could disable Service Workers via the about:config preference dom.serviceWorkers.enabled=false, which removes the vulnerable code path but breaks offline/PWA/push functionality for legitimate sites, so this should be treated as temporary until the update lands.

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Same weakness CWE-284 – Improper Access Control

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9.8
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9.8
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CVE-2016-3427 CRITICAL
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CVE-2025-12480 CRITICAL POC
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Same technique Authentication Bypass

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CVE-2023-22515 CRITICAL POC
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CVE-2012-4681 CRITICAL POC
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CVE-2013-2465 CRITICAL POC
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CVE-2011-3544 CRITICAL POC
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CVE-2022-40684 CRITICAL POC
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CVE-2025-61882 CRITICAL POC
9.8
CVE-2024-0012 CRITICAL POC
9.3
CVE-2023-46805 HIGH POC
8.2

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-2026-16407 vulnerability details – vuln.today
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