Skip to main content

Firefox Esr CVE-2026-4696

| EUVDEUVD-2026-14811 CRITICAL
Use After Free (CWE-416)
2026-03-24 mozilla GHSA-h22r-8qx2-2mv3
Information Disclosure Use After Free Memory Corruption Mozilla Firefox Esr
9.8
CVSS 3.1 · NVD
View

Attack ChainAIDerived

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

  1. Access
    Send crafted HTML with malformed text layout
  2. Exploit
    Trigger use-after-free in Layout component
  3. Execution
    Corrupt memory and execute arbitrary code
  4. Impact
    Achieve full system compromise

Vulnerability Assessment

Weakness
CWE
CWE-416
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Memory lifecycle management
MITRE ATT&CK

2 techniques across 2 tactics: Execution, Privilege Escalation

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

The victim must open a crafted web page or document containing malicious content in Mozilla Firefox versions < 149 (or Firefox ESR < 115.34 or < 140.9). Remote unauthenticated attacker can exploit via network without victim interaction required based on CVSS scoring.
Impact

While CVSS and EPSS scores are not provided in the available intelligence, the vulnerability's classification as a use-after-free in a core rendering component suggests high severity. Use-after-free flaws in browser engines are typically exploitable with moderate complexity, requiring an attacker to craft malicious web content that triggers specific text or font rendering paths. The attack vector is network-based (via malicious web pages), requiring no special privileges. The availability of three separate security advisories indicates this was a coordinated, multi-branch fix rather than an isolated issue, suggesting Mozilla considered it sufficiently critical to warrant priority patching. Without explicit KEV or EPSS data, the real-world risk should be assessed as moderate-to-high for users who visit untrusted websites, particularly given the widespread deployment of Firefox and the web-based attack surface. Organizations should prioritize patching, especially for ESR deployments in managed environments.
Exploit ScenarioDerived

An attacker could host a malicious website containing specially crafted fonts or text rendering instructions that trigger the use-after-free condition in Firefox's layout engine. When a user visits the malicious page, the vulnerability is triggered during text measurement or glyph rendering, allowing the attacker to read sensitive data from the browser's memory (such as cached passwords, session tokens, or other sensitive information) or potentially execute arbitrary code with the privileges of the Firefox process. No special user interaction beyond visiting the website is required, making drive-by attacks feasible via compromised legitimate sites, malvertising, or direct phishing.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.0% exploitation probability (EPSS)

Get an e-mail when this CVE is exploited, patched or re-scored. Free account.

Alert me

AnalysisAIv1 – Mar 24, 2026

Unauthenticated remote attackers can achieve arbitrary code execution through a use-after-free memory corruption vulnerability in Firefox's text and font rendering engine, affecting Firefox versions below 149, ESR below 115.34, and ESR below 140.9. The vulnerability requires no user interaction or special privileges and allows complete compromise of confidentiality, integrity, and availability. No patch is currently available.

Earlier versions of this analysis (1)
v1 Mar 24, 2026 - 12:45 CVSS 9.8

A use-after-free vulnerability exists in Firefox's Layout: Text and Fonts component, affecting Firefox versions prior to 149, Firefox ESR prior to 115.34, and Firefox ESR prior to 140.9. This memory safety flaw could allow attackers to read sensitive information from memory or potentially achieve code execution through carefully crafted web content. The vulnerability was reported by Mozilla and addressed across three separate security advisories (MFSA2026-20, MFSA2026-21, MFSA2026-22), indicating broad impact across Firefox release channels.

RemediationAI

Immediately upgrade Mozilla Firefox to version 149 or later, and upgrade Firefox ESR installations to version 115.34 or later (for the ESR 115 branch) or version 140.9 or later (for the ESR 140 branch). Automated update mechanisms in Firefox will deploy patched versions; manual updates are available through the Help menu (Firefox menu > Help > About Firefox) or from https://www.mozilla.org/firefox/. For enterprise environments using Firefox ESR, deploy updates via your standard patch management processes and verify update completion across all endpoints. Users who cannot immediately patch should consider temporarily restricting Firefox usage to trusted websites only and disabling JavaScript for untrusted content as a temporary mitigation, though patching remains the only reliable fix. Review the detailed advisories at https://www.mozilla.org/security/advisories/mfsa2026-20/, https://www.mozilla.org/security/advisories/mfsa2026-21/, and https://www.mozilla.org/security/advisories/mfsa2026-22/ for any additional guidance.

Affected VersionsENISA

Firefox ESR unspecified <140.9
Firefox ESR unspecified <115.34
Firefox unspecified <149

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

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Sign in to check
Technical ContextAI · show details

The vulnerability resides in Firefox's text and font rendering subsystem, which is responsible for parsing, measuring, and displaying font data and text layout operations. Use-after-free vulnerabilities occur when memory is accessed after it has been deallocated, typically when an object's lifecycle management fails or when reference counting is incorrect. In the context of text rendering, this could manifest when font objects, glyph caches, or text layout structures are freed prematurely while still referenced by active rendering operations. The affected products identified via CPE are Mozilla Firefox (all versions) and Mozilla Firefox ESR (all versions), with the ESR branches maintaining separate version tracks for extended support customers. The root cause falls under CWE categories related to improper memory management and use-after-free conditions common in C/C++ rendering engines.

Know when Firefox Esr gets its next vulnerability

  • Watch products and get an email when something new is published
  • Check this CVE against your own stack and servers
  • Exploit and PoC references, threat intelligence from 22 sources
Continue with Google Continue with GitHub

No credit card · 7-day full trial

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

Use-after-free in the Layout: Text and Fonts component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

Executive ViewAI

Why It Matters

CVE-2026-4696 presents critical security risk, a use-after-free vulnerability 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) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.

Threat Intelligence Overview

EPSS Score
0.0%
Top 95% 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

Use After Free HIGH

Use-after-free vulnerabilities occur when a program continues to access memory through a pointer after that memory has been deallocated.

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.

Related Vulnerabilities in Firefox Multiple Memory and Boundary Vulnerabilities

View all 27
CVE-2026-4712 HIGH
7.5
CVE-2026-4714 HIGH
7.5
CVE-2026-4715 CRITICAL
9.1
CVE-2026-4717 CRITICAL
9.8
CVE-2026-4718 HIGH
8.1
CVE-2026-4719 HIGH
7.5
CVE-2026-4720 CRITICAL
9.8
CVE-2026-4726 HIGH
7.5
CVE-2026-4708 HIGH
7.5
CVE-2026-4713 HIGH
7.5
CVE-2026-4722 HIGH
8.8
CVE-2026-4693 HIGH
7.5
CVE-2026-4729 CRITICAL
9.8
CVE-2026-4695 HIGH
7.5
CVE-2026-4697 HIGH
7.5
CVE-2026-4698 CRITICAL
9.8
CVE-2026-4700 CRITICAL
9.8
CVE-2026-4701 CRITICAL
9.8
CVE-2026-4702 CRITICAL
9.8
CVE-2026-4704 HIGH
7.5
CVE-2026-4706 HIGH
7.5
CVE-2026-4707 HIGH
7.5
CVE-2026-4709 HIGH
7.5
CVE-2026-4710 CRITICAL
9.8
CVE-2026-4711 CRITICAL
9.8
CVE-2026-4723 CRITICAL
9.8

More in Firefox Esr

View all
CVE-2015-4000 LOW POC
3.7 May 21

The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not pro
CVE-2020-26950 HIGH POC
8.8 Dec 09

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable

CVE-2026-4689 CRITICAL POC
10.0 Mar 24

A sandbox escape vulnerability exists in Firefox's XPCOM component due to incorrect boundary conditions and integer over
CVE-2022-29917 CRITICAL POC
9.8 Dec 22

Mozilla developers Andrew McCreight, Gabriele Svelto, Tom Ritter and the Mozilla Fuzzing Team reported memory safety bug
CVE-2014-1568 HIGH
7.5 Sep 25

Mozilla Network Security Services (NSS) before 3.16.2.1, 3.16.x before 3.16.5, and 3.17.x before 3.17.1, as used in Mozi
CVE-2022-26384 CRITICAL POC
9.6 Dec 22

If an attacker could control the contents of an iframe sandboxed with <code>allow-popups</code> but not <code>allow-scri
CVE-2022-34484 HIGH POC
8.8 Dec 22

The Mozilla Fuzzing Team reported potential vulnerabilities present in Thunderbird 91.10. Rated high severity (CVSS 8.8)
CVE-2022-28281 HIGH POC
8.8 Dec 22

If a compromised content process sent an unexpected number of WebAuthN Extensions in a Register command to the parent pr
CVE-2022-26381 HIGH POC
8.8 Dec 22

An attacker could have caused a use-after-free by forcing a text reflow in an SVG object leading to a potentially exploi
CVE-2022-22756 HIGH POC
8.8 Dec 22

If a user was convinced to drag and drop an image to their desktop or other folder, the resulting object could have been
CVE-2022-22740 HIGH POC
8.8 Dec 22

Certain network request objects were freed too early when releasing a network request handle. Rated high severity (CVSS

CVE-2022-22738 HIGH POC
8.8 Dec 22

Applying a CSS filter effect could have accessed out of bounds memory. Rated high severity (CVSS 8.8), this vulnerabilit

Same weakness CWE-416 – Use After Free

View all
CVE-2019-0708 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2014-0322 HIGH POC
8.8
CVE-2012-4792 HIGH POC
8.8
CVE-2009-4324 HIGH POC
7.8
CVE-2015-0313 CRITICAL POC
9.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2013-2551 HIGH POC
8.8

Same technique Information Disclosure

View all
CVE-2019-2725 CRITICAL POC
9.8
CVE-2021-34523 CRITICAL POC
9.0
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2025-68613 HIGH POC
8.8
CVE-2015-1701 HIGH POC
7.8
CVE-2017-0147 HIGH POC
7.5

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-2026-4696 ADVISORY https://vuldb.com/?id.352741 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-2026-4696 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2020190 REF https://bugzilla.redhat.com/show_bug.cgi?id=2450740 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4696.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/

Search Externally

GitHub PoC Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy