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Firefox CVE-2026-6786

| EUVDEUVD-2026-24127 HIGH
Out-of-bounds Write (CWE-787)
2026-04-21 mozilla
Buffer Overflow Memory Corruption Mozilla RCE
7.5
CVSS 3.1 · Vendor: mozilla
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Severity by source

Vendor (mozilla) PRIMARY
7.5 HIGH
AV:N/AC:H/PR:N/UI:R/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
7.5 HIGH
qualitative

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

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

Lifecycle Timeline

7
CVSS changed
May 26, 2026 - 20:22 NVD
8.1 (HIGH) 7.5 (HIGH)
Patch released
Apr 29, 2026 - 02:30 nvd
Patch available
Re-analysis Queued
Apr 27, 2026 - 19:07 vuln.today
cvss_changed
Analysis Generated
Apr 26, 2026 - 20:07 vuln.today
EUVD ID Assigned
Apr 21, 2026 - 13:15 euvd
EUVD-2026-24127
Analysis Generated
Apr 21, 2026 - 13:15 vuln.today
CVE Published
Apr 21, 2026 - 12:41 nvd
HIGH 8.1

DescriptionCVE.org

Memory safety bugs present in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. 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 was fixed in Firefox 150 and Firefox ESR 140.10.

AnalysisAI

Multiple memory corruption bugs in Firefox ESR 140.9, Firefox 149, Thunderbird ESR 140.9, and Thunderbird 149 could enable remote code execution against users visiting malicious websites. Mozilla has fixed these memory safety vulnerabilities in Firefox 150 and Firefox ESR 140.10, with vendor advisories (MFSA2026-30, MFSA2026-32, MFSA2026-33, MFSA2026-34) confirming patches are available. EPSS score of 0.05% (14th percentile) indicates low observed exploitation probability, and no public exploit identified at time of analysis, though SSVC framework assesses total technical impact if successfully weaponized.

Technical ContextAI

This CVE represents a collection of memory safety bugs classified as CWE-787 (Out-of-bounds Write), commonly referred to as buffer overflows. These vulnerabilities exist within Firefox's C++ rendering engine and browser components, where improper bounds checking during memory operations allows writing data beyond allocated buffer boundaries. The affected products span both standard Firefox browser (version 149) and Extended Support Release (ESR 140.9) channels, as well as Thunderbird email client variants built on the same Gecko engine codebase. Memory corruption vulnerabilities in browsers are particularly critical because they operate in the context of rendering untrusted web content, providing attack surface through HTML, CSS, JavaScript, WebAssembly, or media codecs. The bugzilla reference lists over 100 individual bug IDs (2010727 through 2030370), indicating this is Mozilla's typical bundled memory safety advisory covering multiple distinct issues discovered through fuzzing, static analysis, and internal security audits during the development cycle.

RemediationAI

Upgrade immediately to Firefox 150 or later for standard release channel users (MFSA2026-32 at https://www.mozilla.org/security/advisories/mfsa2026-32/). Organizations and users on Extended Support Release channels must upgrade to Firefox ESR 140.10 or later (MFSA2026-30 at https://www.mozilla.org/security/advisories/mfsa2026-30/). Thunderbird users should upgrade to Thunderbird 150 or later (MFSA2026-33 at https://www.mozilla.org/security/advisories/mfsa2026-33/), while Thunderbird ESR users require version 140.10 or later (MFSA2026-34 at https://www.mozilla.org/security/advisories/mfsa2026-34/). No workarounds exist for memory corruption vulnerabilities of this nature - patching is the only effective remediation. If immediate patching is impossible, compensating controls include restricting browser usage to trusted websites only via allowlist proxy filtering, disabling JavaScript through browser policies (breaks most modern websites, suitable only for reading static documentation), running browsers in isolated virtual machines or sandboxed containers to limit post-exploitation impact, and deploying endpoint detection and response (EDR) tools configured to detect abnormal browser process behavior such as shellcode execution or unexpected child process creation. These compensating controls significantly degrade user experience and productivity while providing only partial risk reduction.

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Same weakness CWE-787 – Out-of-bounds Write

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CVE-2014-1761 HIGH POC
7.8
CVE-2009-3129 HIGH POC
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CVE-2021-1732 HIGH POC
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CVE-2013-3346 CRITICAL POC
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Same technique Buffer Overflow

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CVE-2017-7269 CRITICAL POC
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CVE-2015-5119 CRITICAL POC
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CVE-2011-2462 CRITICAL POC
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CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
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CVE-2017-11882 HIGH POC
7.8
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7.8

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 Server 16.0 SUSE Linux Enterprise Server for SAP applications 16.0 Fixed
openSUSE Leap 16.0 Fixed

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CVE-2026-6786 vulnerability details – vuln.today
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