# CVE-2026-109724: Firefox use-after-free in DOM: Core & HTML

Source: https://junglewise.ai/threats/cve-2026-109724-use-after-free-in-the-dom-core-html-component-this-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-13. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-109724 · Severity: medium · CVSS 5.4 · Published 2026-10-13

Firefox, an open-source web browser used by millions worldwide, contains a use-after-free vulnerability in its DOM handling code. This memory safety bug could allow an attacker to execute arbitrary code when a user visits a malicious website, potentially compromising their system and personal data.

Technologies: [Mozilla Firefox](https://junglewise.ai/threats/technologies/firefox), [Mozilla Firefox ESR](https://junglewise.ai/threats/technologies/firefox-esr), [Mozilla Thunderbird](https://junglewise.ai/threats/technologies/thunderbird), [Mozilla Thunderbird ESR](https://junglewise.ai/threats/technologies/thunderbird-esr). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2026-109724 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109724 being exploited in the wild.

**How severe is CVE-2026-109724?** Medium severity, with a CVSS score of 5.4, published 13 October 2026.

**Which products and versions are affected?** Mozilla Firefox before 158; Mozilla Firefox ESR before 153.5; Mozilla Thunderbird before 158; Mozilla Thunderbird ESR before 153.5.

**Is there a fix for CVE-2026-109724?** Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird ESR 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109724 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-109724?** Check whether you run Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird ESR 153.5

## Technical details

A use-after-free vulnerability exists in the DOM: Core & HTML component of Firefox's rendering engine. The flaw allows an attacker to access memory that has been freed, potentially leading to arbitrary code execution when processing specially crafted web content. This vulnerability affects Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR.

## Affected products

- Mozilla Firefox before 158
- Mozilla Firefox ESR before 153.5
- Mozilla Thunderbird before 158
- Mozilla Thunderbird ESR before 153.5

## Timeline

- 2026-10-13: advisory

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2074193](https://bugzilla.mozilla.org/show_bug.cgi?id=2074193)
- [https://www.mozilla.org/security/advisories/mfsa2026-106/](https://www.mozilla.org/security/advisories/mfsa2026-106/)

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