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Mozilla Firefox CVE-2026-74934

| EUVDEUVD-2026-60743 HIGH
Information Exposure (CWE-200)
2026-08-18 mozilla GHSA-fwhj-g32m-x3vf
Information Disclosure Mozilla
7.5
CVSS 3.1 · Vendor: mozilla
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Attacker crafts malicious WebGL canvas page
  2. Delivery
    Victim visits page via phishing or malvertising
  3. Exploit
    WebGL rendering triggers site isolation boundary flaw
  4. Execution
    Cross-origin data exposed to attacker page context
  5. Impact
    Sensitive session or page content exfiltrated to attacker

Vulnerability Assessment

Weakness
CWE
CWE-200
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V14 - Data Protection Data exposure prevention
MITRE ATT&CK

2 techniques across 2 tactics: Collection, Discovery

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Exploitation Conditions

Exploitation requires the victim to visit a malicious web page, satisfying the UI:R requirement in the CVSS vector. No attacker authentication or privileges are required (PR:N). High Attack Complexity (AC:H) indicates that specific technical conditions must be met - likely involving precise timing or cross-origin resource co-loading alongside the WebGL operation - though the exact requirements are not detailed in the public description. The victim must be running an unpatched Firefox version (any standard release prior to 154, or any ESR prior to the respective patched build). WebGL must be enabled, which is the default state in Firefox. No specific non-default configuration or platform restriction is identified; the flaw applies to Firefox on all supported operating systems.
Impact

The provided CVSS 3.1 vector (AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H, score 7.5) reflects meaningful impact, but the real-world risk is moderated by several factors. High Attack Complexity (AC:H) indicates conditions beyond simple page visitation are required, and the EPSS score of 0.16% at the 6th percentile reflects minimal automated exploitation pressure at time of analysis. There is no CISA KEV listing and no confirmed public proof-of-concept code. A notable discrepancy exists between the CWE-200 (information disclosure) characterization and the I:H/A:H CVSS impact components - a pure site isolation information leak would normally affect only confidentiality, and defenders should verify the integrity and availability ratings directly against Mozilla's published advisories before elevating incident priority on that basis. The no-privileges-required, network-accessible nature of the flaw is a genuine concern for consumer and enterprise deployments alike, but user interaction (UI:R) remains a meaningful friction point.
Exploit ScenarioDerived

An attacker hosts a malicious web page containing crafted WebGL canvas content engineered to trigger the site isolation boundary flaw. When a user visits the page - potentially delivered via phishing or a malicious advertisement - the WebGL operation causes the browser to expose data from a cross-origin context, such as content loaded in a co-located banking or webmail tab. No confirmed public POC exists, and AC:H suggests additional setup complexity is required beyond simple page load.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 21, 2026

Site isolation bypass in Firefox's Graphics: CanvasWebGL component allows a malicious web page to leak cross-origin data through the browser's graphics subsystem. All Firefox releases prior to version 154 are affected, along with ESR branches fixed in 115.39, 140.14, and 153.1. No public exploit code or active exploitation has been confirmed; EPSS places this in the 6th percentile, suggesting widespread automated exploitation is currently unlikely despite the High CVSS score.

RemediationAI

Standard channel users should upgrade to Firefox 154 or later. Enterprise ESR users should identify their active ESR branch and upgrade to the corresponding fixed release: Firefox ESR 115.39, Firefox ESR 140.14, or Firefox ESR 153.1. Mozilla's advisories at https://www.mozilla.org/security/advisories/mfsa2026-74/ through mfsa2026-80/ provide branch-specific guidance and changelogs. Where immediate patching is not feasible, disabling WebGL via about:config by setting webgl.disabled to true eliminates the vulnerable attack surface at the cost of breaking WebGL-dependent web applications, which is a significant trade-off for most environments. Browser isolation proxies or restricting navigation to known-safe sites are additional compensating controls with lower application-compatibility impact.

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Technical ContextAI · show details

The root cause is CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) within Firefox's CanvasWebGL subsystem, which implements the WebGL API through HTML canvas elements. Site isolation is a browser security architecture that confines each web origin to a separate process, preventing cross-origin memory or render-output access. A flaw in how CanvasWebGL enforces these boundaries allows graphical or memory content from one origin to be observable by another. CPE data (cpe:2.3:a:mozilla:firefox:*) confirms the affected product spans all Firefox channels - both standard and all ESR (Extended Support Release) branches - prior to the patched versions.

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Severity by source

Vendor (mozilla) PRIMARY 7.5 HIGH
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
vuln.today AI 6.1 MEDIUM

Site isolation bypass inherently crosses origin boundaries warranting S:C; CWE-200 description supports only C:H impact; I:H and A:H from the provided vector are not supported by information-disclosure framing.

3.1 AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:N/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N
SUSE HIGH
Red Hat 7.5 HIGH

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

3
CVSS changed
Aug 21, 2026 - 21:22 NVD
7.5 (HIGH)
CVE Published
Aug 18, 2026 - 12:23 cve.org
HIGH 7.5
CVE Published
Aug 18, 2026 - 12:23 cve.org
UNKNOWN (no severity yet)

DescriptionCVE.org

Site isolation issue in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.

Executive ViewAI

Why It Matters

Firefox versions prior to 154 contain a site isolation bypass vulnerability (CVE-2026-74934) enabling malicious websites to extract cross-origin data through the browser's graphics subsystem; no public exploit identified at time of analysis. This directly compromises user data confidentiality across organizations relying on Firefox, particularly where sensitive cross-origin services are accessed. With no currently available patch, organizations must implement interim controls while preparing for deployment of patched versions 154, ESR 115.39, 140.14, and 153.1.

Business Impact: High
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations include enforcing restrictive Content-Security-Policy (CSP) headers on sensitive cross-origin resources, disabling graphics acceleration where feasible, limiting JavaScript access to cross-origin content, and restricting Firefox usage to isolated network segments for users accessing sensitive data. Continuously monitor vendor advisories for Firefox 154, ESR 115.39, 140.14, and 153.1 availability.

Threat Intelligence Overview

EPSS Score
0.2%
Top 94% exploitable
Prevalence
High
Firefox is a major global browser with broad enterprise and consumer deployment.
Data Quality
6 sources
Confidence: High
EUVD 🇯🇵JVN NVD CVE.org EPSS Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact
High

Priority Score

38
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +38
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)CVE.org

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

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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

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-74934 ADVISORY https://vuldb.com/vuln/391587 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:3658/ REF https://bugzilla.mozilla.org/show_bug.cgi?id=2050584 REF https://www.mozilla.org/security/advisories/mfsa2026-74/ REF https://www.mozilla.org/security/advisories/mfsa2026-75/ REF https://www.mozilla.org/security/advisories/mfsa2026-76/ REF https://www.mozilla.org/security/advisories/mfsa2026-77/ REF https://www.mozilla.org/security/advisories/mfsa2026-78/ REF https://www.mozilla.org/security/advisories/mfsa2026-79/ REF https://www.mozilla.org/security/advisories/mfsa2026-80/

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