Firefox Esr EUVD-2026-14796

| CVE-2026-4686 HIGH

Improper Check for Unusual or Exceptional Conditions (CWE-754)

2026-03-24 mozilla

GHSA-x3f3-63g4-54j4

Information Disclosure Mozilla Firefox Esr

7.5

CVSS 3.1 · NVD

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Attack ChainAIDerived

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

Access

Craft malicious Canvas2D drawing commands
Exploit

Trigger boundary condition error in graphics parser
Execution

Cause memory access violation
Impact

Crash Firefox process

Vulnerability Assessment

Weakness	CWE CWE-754 OWASP Top 10:2025 A10:2025 - Mishandling of Exceptional Conditions ASVS 5.0 V16 - Security Logging and Error Handling Unusual condition handling
Exploitation Conditions	The victim must visit a malicious website or view crafted HTML content containing Canvas2D operations in Firefox versions < 149, < 115.34 ESR, or < 140.9 ESR. No authentication required. Remote unauthenticated exploitation.
Impact	While CVSS and EPSS scores are not available for this CVE, the vulnerability's classification as an information disclosure issue in a widely-used browser component represents moderate real-world risk. The attack vector appears to be network-based (requiring user interaction with malicious web content), and no CVSS vector data is provided to assess attack complexity or privilege requirements. The absence of reported active exploitation or public proof-of-concept code suggests this is not currently being weaponized at scale. However, the boundary condition nature of the flaw and its location in graphics rendering code—which processes untrusted content from web pages—means the technical impact is concrete and exploitable. The fact that Mozilla issued security advisories (MFSA2026-20, MFSA2026-21, MFSA2026-22) across multiple branches indicates this was treated as a priority fix requiring coordination across stable and ESR release tracks.
Exploit ScenarioDerived	An attacker could craft a malicious web page containing specially crafted HTML5 Canvas2D drawing operations that exploit the boundary condition flaw. When a user visits this page in a vulnerable Firefox browser, the Canvas2D component processes the operations without properly validating memory boundaries, causing sensitive data from adjacent memory regions to be leaked. The attacker could then exfiltrate this data via JavaScript, potentially recovering session tokens, cached data, or other sensitive information resident in the browser's memory space. The low attack complexity (requiring only a web page visit) makes this a practical attack vector for targeted or mass exploitation scenarios.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 24, 2026

An incorrect boundary condition vulnerability exists in Firefox's Graphics Canvas2D component that can lead to information disclosure. This affects Firefox versions prior to 149, Firefox ESR versions prior to 115.34, and Firefox ESR versions prior to 140.9. An attacker can exploit this boundary condition issue to disclose sensitive information through crafted Canvas2D operations, though no active exploitation or public proof-of-concept has been reported at this time.

RemediationAI

Users should immediately upgrade Firefox to version 149 or later, Firefox ESR to version 115.34 or later, or Firefox ESR to version 140.9 or later, depending on their release channel. These patched versions are available through the automatic update mechanism in Firefox (Settings > About Firefox) or via manual download from https://www.mozilla.org/firefox/new/. Organizations managing Firefox deployments should prioritize patching given the information disclosure nature of the vulnerability and the ease of delivery via web-based attack vectors. Until patching is completed, users may reduce risk by disabling JavaScript in untrusted web contexts, though this may impact web functionality.

Affected VersionsENISA

Firefox unspecified <149

Firefox ESR unspecified <115.34

Firefox ESR unspecified <140.9

Affected Packages

euvd firefox_esr_unspecified fix: 115.34, 140.9

euvd firefox_unspecified fix: 149

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in euvd

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Technical ContextAI · show details

The vulnerability resides in the Canvas2D graphics rendering component of Mozilla Firefox, which is responsible for 2D drawing operations on HTML5 canvas elements. Canvas2D implements various drawing primitives and image manipulation functions that require precise boundary checking to prevent out-of-bounds memory access. The root cause is classified under incorrect boundary conditions (a memory safety concern), where the component fails to properly validate array or buffer boundaries during canvas operations. This affects the Firefox browser engine across multiple release channels: stable Firefox releases (cpe:2.3:a:mozilla:firefox), the Extended Support Release branch (cpe:2.3:a:mozilla:firefox_esr), indicating the flaw exists in core rendering code used across all Firefox distributions.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SUSE HIGH

Red Hat 7.5 HIGH

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

2

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

CVE Published

Mar 24, 2026 - 12:30 nvd

HIGH 7.5

DescriptionNVD

Incorrect boundary conditions in the Graphics: Canvas2D component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

Executive ViewAI

Why It Matters

CVE-2026-4686 presents notable security risk rated CVSS 7.5. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and consider compensating controls in the interim.

Business Impact: High

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score

0.0%

Top 96% exploitable

Data Quality

7 sources

Confidence: High

EUVD

CVE.org

EPSS

Vulnrichment 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 0.0%

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

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact

High

Technical Impact

Partial

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.

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Vendor StatusVendor

Debian

firefox

Release	Status	Fixed Version	Urgency
sid	vulnerable	148.0.2-1	-
(unstable)	fixed	(unfixed)	-

firefox-esr

Release	Status	Fixed Version	Urgency
bullseye	vulnerable	115.14.0esr-1~deb11u1	-
bullseye (security)	vulnerable	140.8.0esr-1~deb11u1	-
bookworm	vulnerable	128.14.0esr-1~deb12u1	-
bookworm (security)	vulnerable	140.8.0esr-1~deb12u1	-
trixie (security), trixie	vulnerable	140.8.0esr-1~deb13u1	-
forky, sid	vulnerable	140.8.0esr-1	-
(unstable)	fixed	(unfixed)	-

SUSE

Severity: High

Product	Status
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Image SLES15-SP6-SAP-Azure-LI-BYOS Image SLES15-SP6-SAP-Azure-LI-BYOS-Production Image SLES15-SP6-SAP-Azure-VLI-BYOS Image SLES15-SP6-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production	Affected
SUSE Liberty Linux 10	Fixed
SUSE Liberty Linux 8	Fixed
SUSE Liberty Linux 9	Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7	Fixed

References

Advisories & patches

ADVISORY https://access.redhat.com/errata/RHSA-2026:5930 ADVISORY https://access.redhat.com/errata/RHSA-2026:5931 ADVISORY https://access.redhat.com/errata/RHSA-2026:5932 ADVISORY https://access.redhat.com/errata/RHSA-2026:6188 ADVISORY https://access.redhat.com/errata/RHSA-2026:6342 ADVISORY https://access.redhat.com/errata/RHSA-2026:6917 ADVISORY https://access.redhat.com/errata/RHSA-2026:7837 ADVISORY https://access.redhat.com/errata/RHSA-2026:7838 ADVISORY https://access.redhat.com/errata/RHSA-2026:7839 ADVISORY https://access.redhat.com/errata/RHSA-2026:7840 ADVISORY https://access.redhat.com/errata/RHSA-2026:7841 ADVISORY https://access.redhat.com/errata/RHSA-2026:7842 ADVISORY https://access.redhat.com/errata/RHSA-2026:7843 ADVISORY https://access.redhat.com/errata/RHSA-2026:7845 ADVISORY https://access.redhat.com/errata/RHSA-2026:7858 ADVISORY https://access.redhat.com/errata/RHSA-2026:8284 ADVISORY https://access.redhat.com/errata/RHSA-2026:8285 ADVISORY https://access.redhat.com/errata/RHSA-2026:8286 ADVISORY https://access.redhat.com/errata/RHSA-2026:8287 ADVISORY https://access.redhat.com/errata/RHSA-2026:8288 ADVISORY https://access.redhat.com/errata/RHSA-2026:8289 ADVISORY https://access.redhat.com/errata/RHSA-2026:8290 ADVISORY https://access.redhat.com/errata/RHSA-2026:8315 ADVISORY https://access.redhat.com/errata/RHSA-2026:8427 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-4686 ADVISORY https://vuldb.com/?id.352733 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1126/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1127/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1163/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:20978/ REF https://access.redhat.com/errata/RHSA-2026:8850 REF https://access.redhat.com/security/cve/CVE-2026-4686 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2016351 REF https://bugzilla.redhat.com/show_bug.cgi?id=2450734 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4686.json REF https://www.mozilla.org/security/advisories/mfsa2026-20/ REF https://www.mozilla.org/security/advisories/mfsa2026-21/ REF https://www.mozilla.org/security/advisories/mfsa2026-22/ REF https://www.mozilla.org/security/advisories/mfsa2026-23/ REF https://www.mozilla.org/security/advisories/mfsa2026-24/

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