Quick answers
- Is CVE-2026-109708 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-109708 being exploited in the wild.
- How severe is CVE-2026-109708?
- Critical severity, with a CVSS score of 9.6, 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-2026-109708?
- 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-2026-109708 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-109708?
- 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
Incorrect boundary condition validation in Firefox's Networking component permits sandbox escape. The vulnerability requires network-level attack capability and likely user interaction (visiting a malicious webpage), enabling an attacker to execute arbitrary code with the privileges of the browser process and circumvent the sandbox isolation mechanism.
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