CVE-2026-12291: Use-after-free in the Networking: HTTP component

Published Jun 16, 2026
·
Updated

Use-after-free in the Networking: HTTP component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

Affected Software

10 affected componentsFixes available
Mozilla Firefox ESR<140.12
140.12
Mozilla Firefox<152
152
Mozilla Firefox ESR<115.37
115.37
Mozilla Thunderbird<140.12
140.12
Mozilla Thunderbird<152
152
Mozilla Firefox<115.37.0
Mozilla Firefox<152.0.0
Mozilla Firefox>=128.0<140.12.0
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 to a fixed release to a version that resolves this vulnerability.

    Fixed in 115.37
  4. Upgrade

    Upgrade Mozilla Firefox to a version that resolves this vulnerability.

    Fixed in 152
  5. Upgrade

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

    Fixed in 140.12
  6. Upgrade

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

    Fixed in 115.37
  7. Upgrade

    Upgrade Mozilla Thunderbird to a version that resolves this vulnerability.

    Fixed in 152
  8. Upgrade

    Upgrade Mozilla Thunderbird 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·02:03 PM
DescriptionSeverityAffected Software

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Free Weekly Intel

Don't miss critical vulnerabilities

Join thousands of security professionals who receive our weekly digest of trending CVEs, zero-days, and exploited vulnerabilities.

No spam. Unsubscribe anytime.

Frequently Asked Questions

1

What is the severity of CVE-2026-12291?

The severity of CVE-2026-12291 is high, with a CVSS score of 8.8.

2

How do I fix CVE-2026-12291?

To fix CVE-2026-12291, update to Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, or Thunderbird 140.12.

3

What types of software are affected by CVE-2026-12291?

CVE-2026-12291 affects Mozilla Firefox, Mozilla Thunderbird, and Mozilla Firefox ESR.

4

What is the nature of the vulnerability described in CVE-2026-12291?

CVE-2026-12291 is classified as a use-after-free vulnerability in the Networking: HTTP component.

5

When was CVE-2026-12291 published?

CVE-2026-12291 was published on June 16, 2026.

Company

Resources

Contact

SecAlerts Pty Ltd.
132 Wickham Terrace
Fortitude Valley,
QLD 4006, Australia
info@secalerts.co
By using SecAlerts services, you agree to our services end-user license agreement. This website is safeguarded by reCAPTCHA and governed by the Google Privacy Policy and Terms of Service. All names, logos, and brands of products are owned by their respective owners, and any usage of these names, logos, and brands for identification purposes only does not imply endorsement. If you possess any content that requires removal, please get in touch with us.
© 2026 SecAlerts Pty Ltd.
ABN: 70 645 966 203, ACN: 645 966 203