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Mozilla Firefox CVE-2026-74959

| EUVDEUVD-2026-60758 CRITICAL
Protection Mechanism Failure (CWE-693)
2026-08-18 mozilla GHSA-hq5h-hpvx-rq86
Authentication Bypass 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
8.1 HIGH

Remote web-content bug exploitable without auth (PR:N) but realistically requires the victim to load a malicious page (UI:R); high confidentiality/integrity, no availability impact.

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
HIGH
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

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
Aug 21, 2026 - 22:32 vuln.today
CVSS changed
Aug 21, 2026 - 20:22 NVD
9.1 (CRITICAL)
CVE Published
Aug 18, 2026 - 12:23 cve.org
CRITICAL 9.1
CVE Published
Aug 18, 2026 - 12:23 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

Mitigation bypass in the Storage: Cache API component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.

AnalysisAI

Protection-mechanism bypass in the Storage: Cache API of Mozilla Firefox lets remote web content defeat a built-in security mitigation, exposing sensitive data and allowing unauthorized modification (CVSS 9.1, C:H/I:H). All Firefox builds prior to Firefox 154, ESR 140.14, and ESR 153.1 are affected. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Lure victim to malicious page
Delivery
Load crafted Cache API script
Exploit
Bypass Cache API mitigation
Execution
Access or alter cross-boundary data
Impact
Exfiltrate sensitive information
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Vulnerability AssessmentAI

Exploitation Exploitation targets the Storage: Cache API code path, so the concrete prerequisite is that the victim loads attacker-controlled web content in a vulnerable Firefox build (any version before Firefox 154 / ESR 140.14 / ESR 153.1) that exercises CacheStorage/Cache - commonly reached through a Service Worker or page script. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals here conflict and warrant scrutiny. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker lures a Firefox user to a malicious or compromised web page whose script abuses the Cache API to bypass the intended protection mechanism, reading data or influencing content across a security boundary it should not cross. No public exploit code has been identified, and given the CWE-693 nature the attack relies on the victim loading attacker-controlled web content rather than any pre-existing foothold.
Remediation Vendor-released patch: upgrade to Firefox 154, or to Firefox ESR 140.14 or ESR 153.1 if you run an Extended Support Release channel; these are the exact fixed versions and represent the primary and recommended fix. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: identify all systems running Firefox versions prior to 154, ESR 140.14, or ESR 153.1 and communicate the critical patch requirement to IT and desktop support teams. …

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Threat intelligence, references, and detailed analysis are available after sign-in.

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Same technique Authentication Bypass

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
Container suse/kiosk/firefox-esr:140.14-75.12 Affected
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Module for Desktop Applications 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Fixed

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CVE-2026-74959 vulnerability details – vuln.today
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