Firefox Esr EUVD-2026-14813

| CVE-2026-4698 CRITICAL

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

2026-03-24 mozilla

Information Disclosure Memory Corruption Mozilla Firefox Esr

9.8

CVSS 3.1 · NVD

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Attack ChainAIDerived

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

Access

Deliver malicious JavaScript to victim
Exploit

JIT engine 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Weakness	CWE CWE-843 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Type safety enforcement MITRE ATT&CK 1 technique across 1 tactic: Execution The technique list with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 exploits JIT miscompilation in JavaScript Engine. Victim must visit a malicious webpage or open crafted content in Firefox < 149, Firefox ESR < 115.34, or Firefox ESR < 140.9. No special configuration required; default browser configurations are vulnerable.
Impact	The real-world risk of this vulnerability is moderate to significant, despite the absence of CVSS and EPSS scores in the provided intelligence. The information disclosure impact indicates potential for sensitive data leakage from browser memory. Firefox's ubiquity as a widely-used browser means the affected population is substantial. The vulnerability affects three distinct product lines (mainline Firefox and two ESR branches), suggesting it was discovered during active development and backported to legacy versions. No public exploit (POC) is referenced in the available data, and KEV status is not indicated, suggesting this may not be actively exploited in the wild at disclosure time. However, the technical nature of JIT miscompilation—requiring memory corruption to be leveraged—indicates moderate attack complexity. Organizations should prioritize patching given the information disclosure severity and broad user base, though this is not an emergency-tier remote code execution vulnerability.
Exploit ScenarioDerived	An attacker hosts a malicious website containing specially-crafted JavaScript code designed to trigger JIT miscompilation in the target browser. When a user visits the site, the vulnerable JavaScript engine compiles the malicious code into incorrect native machine instructions that access memory outside intended bounds. The miscompiled code then reads and exfiltrates sensitive data such as authentication tokens, session cookies, or other in-memory secrets to the attacker's server. This attack requires no user interaction beyond visiting a website and no special privileges, making it an attractive vector for mass exploitation.

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 miscompilation vulnerability exists in Firefox's JavaScript engine that can lead to information disclosure. This affects Firefox versions below 149, Firefox ESR below 115.34, and Firefox ESR below 140.9. An attacker can exploit this flaw through malicious JavaScript to extract sensitive information from the browser's memory, potentially compromising user data and system security.

RemediationAI

Immediately upgrade Mozilla Firefox to version 149 or later, or upgrade Firefox ESR to version 115.34 or later, or upgrade to version 140.9 or later depending on your deployed ESR branch. These patched versions are available from https://www.mozilla.org/. No partial workarounds exist for JIT miscompilation vulnerabilities; patching is mandatory. Organizations using Firefox in managed environments should deploy automatic updates or enforce version management policies to ensure all users receive the patched versions. Consult the specific security advisories (MFSA2026-20, MFSA2026-21, MFSA2026-22) for detailed patch notes and any platform-specific installation instructions.

Affected VersionsENISA

Firefox ESR unspecified <140.9

Firefox unspecified <149

Firefox ESR unspecified <115.34

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 JIT (Just-In-Time) compilation component of Firefox's JavaScript engine, which is responsible for dynamically compiling JavaScript bytecode into native machine code for performance optimization. JIT miscompilation occurs when the compiler generates incorrect native code from valid JavaScript source, causing memory safety violations. The affected products per CPE are Mozilla Firefox (cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*) and Mozilla Firefox ESR (cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*). While no specific CWE is listed in the provided data, JIT miscompilation typically falls under CWE-94 (Improper Control of Generation of Code) or CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), allowing attackers to read out-of-bounds memory.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

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 7.5 HIGH

Primary rating from NVD.

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

DescriptionNVD

JIT miscompilation in the JavaScript Engine: JIT component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

Zero Day Initiative Advisories

ZDI-26-252 Mozilla Firefox IonMonkey Switch Statement Optimization Type Confusion Remote Code Execution Vulnerability Apr 2026

Executive ViewAI

Why It Matters

CVE-2026-4698 presents critical security risk 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 95% 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 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-2026-4698 ADVISORY https://vuldb.com/?id.352730 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-2026-4698 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2020906 REF https://bugzilla.redhat.com/show_bug.cgi?id=2450719 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4698.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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