# CVE-2026-109752: Mozilla Firefox use-after-free in DOM: Workers component

Source: https://junglewise.ai/threats/cve-2026-109752-use-after-free-in-the-dom-workers-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-2026-109752 · Severity: medium · CVSS 5.4 · Published 2026-10-13

Firefox, a widely-used web browser, contains a use-after-free vulnerability in its DOM Workers component that could allow attackers to crash the browser or potentially execute code. This vulnerability affects Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR across multiple versions. An attacker could exploit this through a malicious website to compromise browser stability or potentially gain unauthorized access.

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-2026-109752 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109752 being exploited in the wild.

**How severe is CVE-2026-109752?** 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-2026-109752?** Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109752 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-109752?** 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 153.5

## Technical details

A use-after-free vulnerability exists in the DOM: Workers component, allowing memory safety violations when worker objects are accessed after being freed. The vulnerability can be triggered through network interaction with a malicious web page; no special user privileges or prior authentication is required. Exploitation could lead to denial of service or arbitrary code execution depending on memory conditions.

## 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: disclosed

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2068407](https://bugzilla.mozilla.org/show_bug.cgi?id=2068407)
- [https://www.mozilla.org/security/advisories/mfsa2026-106/](https://www.mozilla.org/security/advisories/mfsa2026-106/)

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