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Firefox Esr CVE-2026-5734

| EUVDEUVD-2026-19614 CRITICAL
Out-of-bounds Write (CWE-787)
2026-04-07 mozilla
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
8.1 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat
8.8 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

6
Analysis Updated
Apr 16, 2026 - 05:45 EUVD-patch-fix
executive_summary
Re-analysis Queued
Apr 16, 2026 - 05:29 backfill_euvd_patch
patch_released
Patch available
Apr 16, 2026 - 05:29 EUVD
149.0.2,140.9.1
EUVD ID Assigned
Apr 07, 2026 - 13:00 euvd
EUVD-2026-19614
Analysis Generated
Apr 07, 2026 - 13:00 vuln.today
CVE Published
Apr 07, 2026 - 12:43 nvd
CRITICAL 9.8

DescriptionNVD

Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 < 149.0.2 and Firefox ESR < 140.9.1.

AnalysisAI

Multiple memory corruption vulnerabilities in Mozilla Firefox (< 149.0.2) and Firefox ESR (< 140.9.1) enable unauthenticated remote code execution with critical CVSS 9.8 severity. These memory safety bugs-including CWE-787 out-of-bounds write issues-affect both standard and Extended Support Release channels, with Mozilla confirming evidence of memory corruption exploitable for arbitrary code execution. No active exploitation confirmed (not in CISA KEV) and no public exploit identified at time of analysis, though CVSS vector indicates network-accessible attack requiring no user interaction.

Technical ContextAI

This vulnerability represents a collection of memory safety bugs in Firefox's core browser engine (Gecko), specifically affecting Firefox 149.0.1, Firefox ESR 140.9.0, Thunderbird 149.0.1, and Thunderbird ESR 140.9.0. The root cause class is CWE-787 (Out-of-bounds Write), a critical memory corruption vulnerability that occurs when software writes data past the end of an allocated buffer. Mozilla's Bugzilla tracking shows eight distinct bug IDs (2022369, 2023026, 2023545, 2023555, 2023958, 2025422, 2025468, 2025492, 2025505), suggesting multiple distinct memory safety issues discovered through Firefox's ongoing security audit processes. The CPE identifiers confirm impact to both mozilla:firefox and mozilla:firefox_esr product lines. Memory corruption in browser engines is particularly severe because browsers process untrusted content from the web, making them prime targets for exploitation through malicious web pages, JavaScript, or media content.

RemediationAI

Immediately upgrade to Firefox version 149.0.2 or later for standard release channel users, and Firefox ESR version 140.9.1 or later for Extended Support Release deployments. Mozilla has released vendor-patched versions addressing all identified memory safety bugs. Download updates through Firefox's built-in update mechanism (Menu > Help > About Firefox triggers automatic update check) or obtain installers directly from mozilla.org. Consult Mozilla Foundation Security Advisories MFSA2026-25 (https://www.mozilla.org/security/advisories/mfsa2026-25/) and MFSA2026-27 (https://www.mozilla.org/security/advisories/mfsa2026-27/) for complete remediation guidance. For enterprise environments using Firefox ESR, prioritize rapid deployment of version 140.9.1 through existing software distribution mechanisms. No effective workarounds exist for memory corruption vulnerabilities of this nature; patching is the only reliable mitigation. Organizations unable to patch immediately should consider temporary browser restrictions or network-layer controls to limit exposure to untrusted web content until upgrades complete.

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Vendor StatusVendor

SUSE

Severity: High
Product Status
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
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Fixed

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CVE-2026-5734 vulnerability details – vuln.today

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