# CVE-2026-109776: Mozilla Firefox race condition in XPCOM component

Source: https://junglewise.ai/threats/cve-2026-109776-race-condition-in-the-xpcom-component-this-vulnerability-was  
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-2026-109776 · Severity: medium · CVSS 4.2 · Published 2026-10-13

Firefox is a web browser used by millions of users to access websites and online services. A race condition in Firefox's XPCOM component could allow an attacker to exploit timing-dependent flaws, potentially leading to memory corruption or information disclosure. This vulnerability has been fixed in the latest versions of Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR.

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-2026-109776 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109776 being exploited in the wild.

**How severe is CVE-2026-109776?** Medium severity, with a CVSS score of 4.2, published 13 October 2026.

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

**Is there a fix for CVE-2026-109776?** 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-2026-109776 attacked?** It is in a web application.

**Am I affected by CVE-2026-109776?** 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 race condition exists in the XPCOM (Cross Platform Component Object Model) component, which is a core component in Firefox and Thunderbird. Race conditions occur when multiple processes or threads access shared resources without proper synchronization, allowing attackers to manipulate application state. Exploitation likely requires local or network access depending on how the component is invoked.

## Affected products

- Mozilla Firefox below 158
- Mozilla Firefox ESR below 153.5
- Mozilla Thunderbird below 158
- Mozilla Thunderbird ESR below 153.5

## Timeline

- 2026-10-13: disclosed

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2069395](https://bugzilla.mozilla.org/show_bug.cgi?id=2069395)
- [https://www.mozilla.org/security/advisories/mfsa2026-106/](https://www.mozilla.org/security/advisories/mfsa2026-106/)

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