Is CVE-2026-109755 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-109755 being exploited in the wild.

How severe is CVE-2026-109755?

Critical severity, with a CVSS score of 9.6, published 13 October 2026.

Which products and versions are affected?

Mozilla Firefox before 158; Mozilla Thunderbird before 158.

Is there a fix for CVE-2026-109755?

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-2026-109755 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-109755?

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.

CVE-2026-109755: Mozilla Firefox sandbox escape in DOM Content Processes

CVE-2026-109755 · Severity: critical · CVSS 9.6 · Published 2026-10-13

Firefox and Thunderbird, popular web browsers and email clients, contain a sandbox escape vulnerability in the DOM Content Processes component that allows an attacker to break out of the browser's security isolation. Exploitation could grant an attacker access to sensitive user data, installed extensions, and the ability to execute arbitrary code on the system with user privileges.

Technologies: Mozilla Firefox, Mozilla Thunderbird. Vendors: Mozilla.

Quick answers

Is CVE-2026-109755 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-109755 being exploited in the wild.
How severe is CVE-2026-109755?: Critical severity, with a CVSS score of 9.6, published 13 October 2026.
Which products and versions are affected?: Mozilla Firefox before 158; Mozilla Thunderbird before 158.
Is there a fix for CVE-2026-109755?: 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-2026-109755 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-109755?: 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 sandbox escape vulnerability exists in Firefox and Thunderbird's DOM Content Processes component that allows an attacker to escape the browser's isolation sandbox. The vulnerability can be exploited via network attack vector when a user visits a malicious website. Successful exploitation grants arbitrary code execution outside the sandboxed process.

Affected products

Mozilla Firefox before 158
Mozilla Thunderbird before 158

Timeline

2026-10-13: disclosed

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.