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Mozilla CVE-2026-4729

| EUVDEUVD-2026-14873 CRITICAL
Classic Buffer Overflow (CWE-120)
2026-03-24 mozilla GHSA-xh4v-qr89-3hj3
RCE Buffer Overflow Mozilla
9.8
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
    Send crafted webpage to target
  2. Exploit
    Trigger memory safety bug in Firefox parser
  3. Execution
    Corrupt heap memory
  4. Impact
    Execute arbitrary code with browser privileges

Vulnerability Assessment

Weakness
CWE
CWE-120
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Buffer copy size validation
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.

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Exploitation Conditions

The victim must use Firefox versions below 149 or Thunderbird 148. Remote unauthenticated attacker can exploit memory safety bugs through network without user interaction on vulnerable default installations.
Impact

This vulnerability presents a critical real-world risk despite the absence of CVSS and EPSS scores in the provided intelligence. The presence of memory corruption with explicit Mozilla statements that these bugs 'showed evidence of memory corruption' and could be 'exploited to run arbitrary code' indicates high technical impact. The attack vector is likely network-based (delivery via malicious web content), attack complexity is elevated (requires crafting specific memory corruption payloads), and no privileges are required. The fact that this is a Mozilla-reported vulnerability in a major browser affecting millions of users elevates priority substantially. No KEV status or public POC is mentioned, suggesting this may be a proactive disclosure rather than an in-the-wild exploitation report, which is favorable. However, the combination of RCE potential, widespread user base, and memory corruption primitives means this should be treated as critical for any organization with Firefox deployments.
Exploit ScenarioDerived

An attacker crafts a malicious web page containing JavaScript that triggers a specific memory corruption condition in the Gecko engine (e.g., a use-after-free in DOM handling or a buffer overflow in a parsing routine). When a user visits this page in Firefox 148 or earlier, the memory corruption is triggered, allowing the attacker to write arbitrary code to memory and ultimately achieve remote code execution with the privileges of the Firefox process. No prior user authentication or permission requests are required beyond visiting the malicious site.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 24, 2026

Multiple memory safety bugs in Firefox 148 and Thunderbird 148 allow attackers to trigger memory corruption with potential for arbitrary code execution. Firefox versions prior to 149 are vulnerable, as confirmed by Mozilla security advisories. The vulnerability requires no user interaction beyond normal browsing and represents a critical elevation risk due to the presume-exploitable nature of the underlying memory corruption issues.

RemediationAI

Immediately upgrade Firefox to version 149 or later, and upgrade Thunderbird to a patched version (consult https://www.mozilla.org/security/advisories/mfsa2026-20/ for Thunderbird version specifics). For enterprise deployments, prioritize Firefox patching within 24-48 hours given the RCE potential. Organizations unable to patch immediately should consider temporarily disabling JavaScript execution for untrusted content via security policies, restricting browsing to trusted internal sites only, or deploying browser isolation solutions. Monitor Mozilla security advisories at https://www.mozilla.org/security/advisories/ for any indicators of active exploitation or related vulnerabilities.

Affected VersionsENISA

Firefox unspecified <149

Affected Packages

euvd firefox_unspecified fix: 149

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

These vulnerabilities represent classic memory safety issues in Mozilla's Gecko rendering engine and browser codebase, which are implemented in C/C++ and inherently susceptible to buffer overflows and use-after-free conditions. The affected products (Firefox and Thunderbird, identified via CPE cpe:2.3:a:mozilla:firefox) are large-scale, user-facing applications that parse untrusted web content and execute JavaScript. While specific CWE classifications are not provided in the intelligence, the tags indicate buffer overflow vulnerabilities, which typically fall under CWE-120 (Buffer Copy without Checking Size of Input) or related memory corruption classes. The Mozilla security advisory references (including bugzilla entries 1944033, 1997282, 2009213, 2011412, 2021925, 2022034) suggest multiple distinct memory safety defects across different components of the Gecko engine.

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  • Exploit and PoC references, threat intelligence from 22 sources
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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
SUSE CRITICAL
Red Hat 7.5 HIGH

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

2
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
CVE Published
Mar 24, 2026 - 12:30 nvd
CRITICAL 9.8

DescriptionCVE.org

Memory safety bugs present in Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149.

Executive ViewAI

Why It Matters

CVE-2026-4729 presents critical security risk, a buffer overflow vulnerability rated CVSS 9.8. Exploitation could allow attackers to corrupt memory, crash the application, or potentially execute arbitrary code. 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) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.

Threat Intelligence Overview

EPSS Score
0.0%
Top 100% exploitable
Data Quality
7 sources
Confidence: High
EUVD NVD 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

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Related Vulnerabilities in Firefox Multiple Memory and Boundary Vulnerabilities

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CVE-2026-4726 HIGH
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CVE-2026-4697 HIGH
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7.5
CVE-2026-4706 HIGH
7.5
CVE-2026-4707 HIGH
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CVE-2026-4709 HIGH
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CVE-2026-4710 CRITICAL
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CVE-2026-4711 CRITICAL
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CVE-2026-4723 CRITICAL
9.8

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The Web IDL implementation in Mozilla Firefox before 28.0, Firefox ESR 24.x before 24.4, Thunderbird before 24.4, and Se
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CVE-2013-0643 HIGH
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The Firefox sandbox in Adobe Flash Player before 10.3.183.67 and 11.x before 11.6.602.171 on Windows and Mac OS X, and b

Same weakness CWE-120 – Classic Buffer Overflow

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Same technique RCE

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CVE-2023-3519 CRITICAL POC
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Vendor StatusVendor

Debian

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

SUSE

Severity: Critical
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-4729 ADVISORY https://vuldb.com/vuln/352760 REF https://access.redhat.com/security/cve/CVE-2026-4729 REF https://bugzilla.mozilla.org/buglist.cgi?bug_id=1944033%2C1997282%2C2009213%2C2011412%2C2021925%2C2022034 REF https://bugzilla.redhat.com/show_bug.cgi?id=2450745 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4729.json REF https://www.mozilla.org/security/advisories/mfsa2026-20/ REF https://www.mozilla.org/security/advisories/mfsa2026-23/

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