# CVE-2026-109779: Firefox race condition in Networking DNS component

Source: https://junglewise.ai/threats/cve-2026-109779-race-condition-in-the-networking-dns-component-this  
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-2026-109779 · Severity: medium · CVSS 4.2 · Published 2026-10-13

Firefox and Thunderbird contain a race condition vulnerability in their DNS networking component that could allow an attacker to exploit timing issues in DNS resolution. This could potentially lead to DNS spoofing, cache poisoning, or other network-level attacks that compromise the integrity of web communications. The vulnerability affects both applications and has been patched in version 158.

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

## Quick answers

**Is CVE-2026-109779 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109779 being exploited in the wild.

**How severe is CVE-2026-109779?** Medium severity, with a CVSS score of 4.2, published 13 October 2026.

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

**Is there a fix for CVE-2026-109779?** Yes: fixed in Firefox 158, Thunderbird 158. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109779 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-109779?** Check whether you run Mozilla Firefox or Mozilla Thunderbird 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, Thunderbird 158

## Technical details

A race condition exists in the DNS resolution component of the networking stack, allowing an attacker to exploit timing windows in concurrent DNS operations. The vulnerability can be triggered remotely through network access without requiring user interaction or prior authentication. An attacker may be able to intercept, redirect, or manipulate DNS queries to perform DNS spoofing or cache poisoning attacks.

## Affected products

- Mozilla Firefox before 158
- Mozilla Thunderbird before 158

## Timeline

- 2026-10-13: disclosed
- 2026-10-13: patched

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2072048](https://bugzilla.mozilla.org/show_bug.cgi?id=2072048)
- [https://www.mozilla.org/security/advisories/mfsa2026-106/](https://www.mozilla.org/security/advisories/mfsa2026-106/)

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