CVE-2026-6786: Memory safety bugs fixed in Firefox ESR 140.10, Thunderbird ESR 140.10, Firefox 150 and Thunderbird 150

Published Apr 21, 2026
·
Updated

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.

Affected Software

7 affected componentsFixes available
Mozilla Firefox ESR<140.10
140.10
Mozilla Firefox<150
150
Mozilla Thunderbird<150
150
Mozilla Thunderbird<140.10
140.10
Mozilla Firefox<150.0
Mozilla Firefox>=140.0<140.10.0
Mozilla Thunderbird>=140.0<140.10.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 140.10
  2. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 150
  3. Upgrade

    Upgrade Mozilla Firefox to a version that resolves this vulnerability.

    Fixed in 150
  4. Upgrade

    Upgrade Mozilla Firefox ESR to a version that resolves this vulnerability.

    Fixed in 140.10
  5. Upgrade

    Upgrade Mozilla Thunderbird to a version that resolves this vulnerability.

    Fixed in 150
  6. Upgrade

    Upgrade Mozilla Thunderbird ESR to a version that resolves this vulnerability.

    Fixed in 140.10

Event History

Apr 21, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
Updated
via Mozilla·12:00 AM
Affected Software
CVE Published
via MITRE·12:41 PM
Data Sourced
via MITRE·12:41 PM
Description
Data Sourced
via Red Hat·02:02 PM
DescriptionSeverityAffected Software
Apr 26, 2026
Data Sourced
via NVD·07:53 PM
DescriptionSeverityWeaknessAffected Software
Aug 26, 58370
Event
via NVD·12:12 PM

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

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Frequently Asked Questions

1

What is the severity of CVE-2026-6786?

CVE-2026-6786 is classified as a high-severity vulnerability due to potential memory corruption issues.

2

How do I fix CVE-2026-6786?

To mitigate CVE-2026-6786, update to Firefox ESR version 140.10, Firefox version 150, or Thunderbird version 150.

3

What software is affected by CVE-2026-6786?

CVE-2026-6786 affects Firefox ESR 140.9 and earlier, Thunderbird ESR 140.9 and earlier, Firefox 149 and earlier, and Thunderbird 149 and earlier.

4

What are the consequences of exploiting CVE-2026-6786?

Exploitation of CVE-2026-6786 could lead to memory corruption, potentially allowing attackers to execute arbitrary code.

5

When was CVE-2026-6786 reported?

CVE-2026-6786 was disclosed in conjunction with the release of the updates in April 2026.

Company

Resources

Contact

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