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Firefox CVE-2026-84129

| EUVDEUVD-2026-69078 CRITICAL
Origin Validation Error (CWE-346)
2026-09-01 mozilla GHSA-vhhv-v3m2-wvqf
Information Disclosure Mozilla Suse
9.8
CVSS 3.1 · Vendor: mozilla
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Severity by source

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
8.2 HIGH

Client-side browser flaw needs the victim to load malicious content (UI:R); site-isolation bypass crosses origins (S:C) with primarily cross-origin data exposure (C:H), minor integrity, no availability impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/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:H/SI:L/SA:N
SUSE
HIGH
qualitative

Primary rating from Vendor (mozilla).

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
Sep 02, 2026 - 16:30 vuln.today
CVSS changed
Sep 02, 2026 - 16:22 NVD
9.8 (CRITICAL)
CVE Published
Sep 01, 2026 - 12:18 cve.org
UNKNOWN (no severity yet)
CVE Published
Sep 01, 2026 - 12:18 cve.org
CRITICAL 9.8

DescriptionCVE.org

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155 and Firefox ESR 153.2.

AnalysisAI

Cross-origin data exposure in Mozilla Firefox arises from a site-isolation defect in the DOM Navigation component, where origin boundaries are not correctly enforced during navigation, potentially letting a malicious page access data belonging to another origin. It affects Firefox before 155 and Firefox ESR before 153.2, and was fixed by Mozilla in those releases (advisories mfsa2026-82/85/86/88). …

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Vulnerability AssessmentAI

Exploitation Exploitation requires the victim to load attacker-controlled web content in a vulnerable Firefox build (before 155 / ESR before 153.2) and requires the crafted navigation sequence in the DOM Navigation component to be exercised - i.e., the site-isolation origin check is only bypassed along this specific navigation path. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The provided CVSS is 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), but that score is inconsistent with the vulnerability class: a client-side browser site-isolation issue realistically requires the victim to navigate to attacker-controlled web content (UI:R), and a CWE-346 origin-validation defect is predominantly a confidentiality/cross-origin-read problem rather than a full I:H/A:H compromise - so the base score appears overstated. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Vendor-released patch: upgrade to Firefox 155 or Firefox ESR 153.2 (or later); consult the Mozilla advisories at https://www.mozilla.org/security/advisories/mfsa2026-82/ and mfsa2026-88 for the exact channel mapping. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, audit your organization's Firefox deployment to identify instances running versions prior to Firefox 155 and Firefox ESR prior to 153.2. …

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected

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CVE-2026-84129 vulnerability details – vuln.today
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