CVE-2026-12309: Memory safety bug fixed in Thunderbird 152

Published Jun 16, 2026
·
Updated

Memory safety bug fixed in Firefox 152. This vulnerability was fixed in Firefox 152 and Firefox ESR 140.12.

Other sources

Memory safety bug fixed in Firefox 152. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

— MITRE

Affected Software

8 affected componentsFixes available
Mozilla Firefox ESR<140.12
140.12
Mozilla Firefox<152
152
Mozilla Thunderbird<140.12
140.12
Mozilla Thunderbird<152
152
Mozilla Firefox<140.12.0
Mozilla Firefox<152.0.0
Mozilla Thunderbird<140.12.0
Mozilla Thunderbird<152.0.0

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 140.12
  2. Upgrade

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

    Fixed in 152
  3. Upgrade

    Upgrade Firefox to a version that resolves this vulnerability.

    Fixed in 152
  4. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 140.12
  5. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 152
  6. Upgrade

    Upgrade Thunderbird 140.12 to a version that resolves this vulnerability.

    Fixed in 140.12

Event History

Jun 16, 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·11:52 AM
Data Sourced
via MITRE·11:52 AM
Description
Data Sourced
via NVD·01:16 PM
DescriptionSeverityWeaknessAffected Software
Data Sourced
via Red Hat·02:02 PM
DescriptionSeverityAffected Software

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-2026-12309?

CVE-2026-12309 has a medium severity rating of 6.5 according to the CVSS 3.1 scoring system.

2

How do I fix CVE-2026-12309?

To mitigate CVE-2026-12309, update to Thunderbird 152 or Firefox 152 as well as their ESR versions.

3

What type of vulnerability is CVE-2026-12309?

CVE-2026-12309 is classified as a memory safety bug associated with a buffer overflow.

4

Which software is affected by CVE-2026-12309?

CVE-2026-12309 affects Mozilla Thunderbird, Mozilla Firefox, and Mozilla Firefox ESR.

5

When was CVE-2026-12309 published?

CVE-2026-12309 was published on June 16, 2026.

Company

Resources

Contact

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