CVE-2026-6785: Firefox & Thunderbird Memory Safety Bugs Allow RCE
The National Vulnerability Database has detailed CVE-2026-6785, a series of high-severity memory safety bugs impacting multiple versions of Firefox, Firefox ESR, and Thunderbird. Specifically, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149, and Thunderbird 149 are all vulnerable. These bugs, categorized under CWE-125 (Out-of-bounds Read), CWE-416 (Use After Free), and CWE-787 (Out-of-bounds Write), exhibited clear signs of memory corruption.
While the National Vulnerability Database indicates that exploiting these bugs for arbitrary code execution would require significant effort, the potential for a sophisticated attacker to achieve remote code execution is undeniable. A CVSS score of 8.1 (HIGH) underscores the critical nature of this vulnerability, especially given the widespread use of these browsers and email clients across enterprises and individual users.
Defenders must prioritize patching. The National Vulnerability Database confirms these issues have been addressed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. Proactive patching is the only viable defense against such fundamental memory corruption flaws, which are consistently favored by attackers for their reliability in achieving code execution.
What This Means For You
- If your organization relies on Firefox or Thunderbird, you need to immediately verify that all installations are updated to Firefox 150, Firefox ESR 115.35, Thunderbird 150, or their respective patched versions. Unpatched systems are exposed to potential remote code execution via CVE-2026-6785, a critical risk for any enterprise.
Related ATT&CK Techniques
🛡️ Detection Rules
3 rules · 6 SIEM formats3 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
CVE-2026-6785: Potential Firefox/Thunderbird RCE via Memory Corruption
title: CVE-2026-6785: Potential Firefox/Thunderbird RCE via Memory Corruption
id: scw-2026-04-26-ai-1
status: experimental
level: high
description: |
Detects the execution of Firefox or Thunderbird with a command line argument containing 'javascript:', which could indicate an attempt to exploit memory safety bugs (CVE-2026-6785) leading to Remote Code Execution. This rule targets the initial access vector by looking for suspicious command-line invocations.
author: SCW Feed Engine (AI-generated)
date: 2026-04-26
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-6785/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: process_creation
detection:
selection:
Image|contains:
- 'firefox.exe'
- 'thunderbird.exe'
CommandLine|contains:
- 'javascript:'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-6785 | Memory Corruption | Firefox ESR versions 115.34 and earlier |
| CVE-2026-6785 | Memory Corruption | Firefox ESR versions 140.9 and earlier |
| CVE-2026-6785 | Memory Corruption | Thunderbird ESR versions 140.9 and earlier |
| CVE-2026-6785 | Memory Corruption | Firefox versions 149 and earlier |
| CVE-2026-6785 | Memory Corruption | Thunderbird versions 149 and earlier |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | April 26, 2026 at 22:53 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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