Is CVE-2026-100819 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-100819 being exploited in the wild.

How severe is CVE-2026-100819?

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 115.x before 115.42, 140.x before 140.17, 153.x before 153.4.

Is there a fix for CVE-2026-100819?

A patch was published on 2026-09-29: Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-100819 attacked?

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

Am I affected by CVE-2026-100819?

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-2026-100819: Mozilla Firefox sandbox escape in XPCOM component

CVE-2026-100819 · Severity: critical · CVSS 9.6 · Published 2026-09-29

Firefox, a web browser used by millions, contains a vulnerability in its XPCOM component that allows an attacker to escape the browser's sandbox security boundary through incorrect code logic. Exploitation could allow malicious code to execute outside the sandbox and access the operating system, potentially compromising the entire system running the browser.

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

Quick answers

Is CVE-2026-100819 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-100819 being exploited in the wild.
How severe is CVE-2026-100819?: 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 115.x before 115.42, 140.x before 140.17, 153.x before 153.4.
Is there a fix for CVE-2026-100819?: A patch was published on 2026-09-29: Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-100819 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-100819?: 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

The vulnerability stems from incorrect boundary condition checks in the XPCOM component, leading to a sandbox escape. This is a memory safety or logic flaw that allows code to break out of Firefox's content process sandbox with no special privileges required. Mozilla has patched this issue in Firefox ESR 153.4, 115.42, 140.17 and Firefox 157.

Affected products

Mozilla Firefox before 157
Mozilla Firefox ESR 115.x before 115.42, 140.x before 140.17, 153.x before 153.4

Timeline

2026-09-29: disclosed
2026-09-29: patched: Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17

References

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