Red Hat EUVD-2026-14821

| CVE-2026-4702 CRITICAL

Access of Resource Using Incompatible Type (Type Confusion) (CWE-843)

2026-03-24 mozilla

GHSA-mrrg-439g-x65p

Information Disclosure Memory Corruption Red Hat Mozilla Suse

Critical

Disputed · 9.8 NVD

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Attack ChainAIDerived

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

Access

Deliver malicious JavaScript to Firefox browser
Exploit

JIT compiler miscompiles code
Execution

Bypass security checks
Impact

Execute arbitrary code with browser privileges

Vulnerability Assessment

Weakness	CWE CWE-843 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Type safety enforcement MITRE ATT&CK 1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Exploitation Conditions	Remote unauthenticated attacker can exploit Firefox versions below 149 (or ESR below 140.9) by delivering crafted JavaScript code. No victim interaction required if malicious script executes automatically on visited webpage. Default Firefox configurations are vulnerable.
Impact	Without CVSS scores, EPSS probability data, or confirmed KEV/active exploitation status provided in the source data, assessment relies on structural factors. The vulnerability affects widely-deployed browsers (Firefox and Firefox ESR) across all versions below specified thresholds, which significantly increases potential impact scope. Information disclosure from JIT miscompilation typically requires specific JavaScript payloads to trigger, suggesting moderate attack complexity, though no POC availability was documented. The fact that Mozilla issued multiple security advisories (MFSA2026-20 and MFSA2026-22) indicates this was treated as a priority security issue. The vulnerability's presence in both standard Firefox and ESR (Extended Support Release) branches suggests widespread exposure. Real-world risk is elevated due to the prevalence of Firefox, the potential for remote exploitation via malicious websites, and the information disclosure impact which could compromise user privacy or enable further attacks. However, without active exploitation evidence or CVSS/EPSS data, this should be prioritized based on user base size and deployment patterns rather than assumed critical severity.
Exploit ScenarioDerived	An attacker could host a malicious webpage containing carefully crafted JavaScript code designed to trigger the JIT miscompilation. When a user visits this page in a vulnerable Firefox browser, the malicious script could exploit the miscompiled code path to read sensitive data from the browser's memory, such as authentication tokens, cached credentials, or data from other browser tabs. The attack requires user interaction (visiting the malicious site) but no special privileges, making it a viable vector for mass exploitation through drive-by attacks or watering hole campaigns.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 24, 2026

A JIT (Just-In-Time) compilation miscompilation vulnerability exists in Firefox's JavaScript Engine that can lead to information disclosure. This affects Firefox versions below 149 and Firefox ESR versions below 140.9. An attacker can exploit this vulnerability through malicious JavaScript code to potentially disclose sensitive information from the browser's memory or process space.

RemediationAI

Upgrade Firefox to version 149 or later, and Firefox ESR to version 140.9 or later immediately. Users should navigate to Help > About Firefox (or Help > About Firefox ESR) which will automatically download and prompt installation of the latest patched version. Organizations managing Firefox deployments should use Mozilla's official security advisories at https://www.mozilla.org/security/advisories/mfsa2026-20/ and https://www.mozilla.org/security/advisories/mfsa2026-22/ to coordinate patching across their environments. Until patching is completed, users should avoid visiting untrusted websites and consider disabling JavaScript in high-risk scenarios, though this significantly impacts web functionality. Additionally, keeping Firefox and Firefox ESR updated with automatic security updates enabled is the primary control to prevent exploitation of JIT miscompilation vulnerabilities.

Affected VersionsENISA

Firefox unspecified <149

Firefox ESR unspecified <140.9

Affected Packages

euvd firefox_esr_unspecified fix: 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 JavaScript Engine component of Mozilla Firefox, specifically in the JIT compiler which translates JavaScript bytecode into native machine code for performance optimization. The affected products are identified via CPE strings cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* and cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*, indicating all versions of both Firefox and Firefox ESR up to the patched releases are potentially vulnerable. JIT miscompilation occurs when the compiler incorrectly optimizes code, potentially causing unintended memory access or state leakage. While a specific CWE was not provided in the vulnerability data, JIT miscompilation issues typically fall under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) or related memory safety categories. The vulnerability's classification as an information disclosure issue suggests the miscompilation allows reading memory that should be restricted from access.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Sources disagree (Medium–Critical)

NVD PRIMARY 9.8 CRITICAL

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

SUSE CRITICAL

Red Hat 6.1 MEDIUM

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 VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

2

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

CVE Published

Mar 24, 2026 - 12:30 nvd

CRITICAL 9.8

DescriptionCVE.org

JIT miscompilation in the JavaScript Engine component. This vulnerability affects Firefox < 149 and Firefox ESR < 140.9.

Executive ViewAI

Why It Matters

Organizations using the JavaScript Engine component. This vulnerability affects Firefox face critical risk from CVE-2026-4702 rated CVSS 9.8. Successful exploitation could critically impact the confidentiality, integrity, and availability of affected systems. Organizations should apply vendor updates immediately when available and implement compensating controls in the interim.

Business Impact: Severe

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

6 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 CRITICAL

CISA KEV No

Public POC No

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

CRITICAL severity

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

Out-of-Cycle

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact

Very High

Technical Impact

Total

Priority Score

49

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +49

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Memory Corruption HIGH

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

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: Critical

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-2026-4702 ADVISORY https://vuldb.com/?id.352748 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://bugzilla.mozilla.org/show_bug.cgi?id=2013560 REF https://www.mozilla.org/security/advisories/mfsa2026-20/ 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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