Is CVE-2026-100811 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-100811 being exploited in the wild.

How severe is CVE-2026-100811?

Critical severity, with a CVSS score of 9.6, published 29 September 2026.

Which products and versions are affected?

Mozilla Firefox before 157; Mozilla Firefox ESR before 153.4 and before 140.17.

Is there a fix for CVE-2026-100811?

A patch was published on 2026-09-29: Firefox 157, Firefox ESR 153.4, and Firefox ESR 140.17 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-100811 attacked?

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

Am I affected by CVE-2026-100811?

Check whether you run Mozilla Firefox or Mozilla Firefox ESR 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-2026-100811: Firefox sandbox escape due to use-after-free in DOM

CVE-2026-100811 · Severity: critical · CVSS 9.6 · Published 2026-09-29

Firefox contains a use-after-free vulnerability in its DOM handling that allows escaping the browser's security sandbox. An attacker could exploit this flaw through a malicious web page to break out of the browser's isolation protections and execute arbitrary code with the privileges of the user browsing the web. This has been patched in recent Firefox releases.

Technologies: Mozilla Firefox, Mozilla Firefox ESR. Vendors: Mozilla.

Quick answers

Is CVE-2026-100811 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-100811 being exploited in the wild.
How severe is CVE-2026-100811?: Critical severity, with a CVSS score of 9.6, published 29 September 2026.
Which products and versions are affected?: Mozilla Firefox before 157; Mozilla Firefox ESR before 153.4 and before 140.17.
Is there a fix for CVE-2026-100811?: A patch was published on 2026-09-29: Firefox 157, Firefox ESR 153.4, and Firefox ESR 140.17 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-100811 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-100811?: Check whether you run Mozilla Firefox or Mozilla Firefox ESR 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.

Technical details

A use-after-free vulnerability in the DOM: Core & HTML component allows sandbox escape in Firefox. The flaw is triggered through a network-based attack vector when processing malicious DOM content. An attacker can craft a webpage that triggers the use-after-free condition, leading to arbitrary code execution with user-level privileges and breaking out of the browser sandbox.

Affected products

Mozilla Firefox before 157
Mozilla Firefox ESR before 153.4 and before 140.17

Timeline

2026-09-29: disclosed
2026-09-29: patched: Firefox 157, Firefox ESR 153.4, and Firefox ESR 140.17

References

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