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Firefox Esr EUVDEUVD-2026-14806

| CVE-2026-4691 CRITICAL
Use After Free (CWE-416)
2026-03-24 mozilla GHSA-h895-88fj-h89r
9.8
CVSS 3.1 · NVD
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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
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from NVD.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 24, 2026 - 12:45 euvd
EUVD-2026-14806
Analysis Generated
Mar 24, 2026 - 12:45 vuln.today
CVE Published
Mar 24, 2026 - 12:30 nvd
CRITICAL 9.8

DescriptionNVD

Use-after-free in the CSS Parsing and Computation component. This vulnerability affects Firefox < 149, Firefox ESR < 115.34, and Firefox ESR < 140.9.

AnalysisAI

Critical use-after-free in Mozilla Firefox's CSS parsing engine enables unauthenticated remote code execution with no user interaction required, affecting Firefox versions below 149, ESR 115.34, and ESR 140.9. An attacker can exploit this memory corruption vulnerability by crafting a malicious web page that triggers the vulnerability when rendered, achieving full system compromise. No patch is currently available.

Technical ContextAI

The vulnerability resides in the CSS Parsing and Computation subsystem of the Gecko rendering engine used by Mozilla Firefox. Use-after-free vulnerabilities occur when memory is accessed after it has been deallocated, potentially allowing attackers to read or manipulate freed memory regions. In the context of CSS parsing, this could occur during the processing of malformed or specially-crafted stylesheets where the parser frees a data structure prematurely but continues to reference it. The affected products are identified via CPE strings cpe:2.3:a:mozilla:firefox and cpe:2.3:a:mozilla:firefox_esr, indicating the vulnerability affects both the main Firefox release channel and the Extended Support Release (ESR) variants used in enterprise environments.

RemediationAI

Users should upgrade Firefox to version 149 or later immediately. Users of Firefox ESR should upgrade to version 115.34 or later, or version 140.9 or later, depending on their deployed ESR track. Detailed patching instructions and availability timelines are provided in the Mozilla security 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 enterprise environments using Firefox ESR, administrators should prioritize deployment of the patched ESR versions through their software distribution infrastructure. Until patches can be applied, limiting browsing to trusted websites and disabling JavaScript execution via extensions may reduce exposure, though these are temporary mitigations only and do not eliminate the underlying vulnerability.

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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

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EUVD-2026-14806 vulnerability details – vuln.today

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