Is CVE-2026-109763 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-109763 being exploited in the wild.

How severe is CVE-2026-109763?

Informational severity, 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-2026-109763?

Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Am I affected by CVE-2026-109763?

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.

CVE-2026-109763: Mozilla Firefox file handling mitigation bypass

CVE-2026-109763 · Severity: info · Published 2026-10-13

Firefox and Thunderbird web browser and email client contain a mitigation bypass vulnerability in the file handling component that could allow an attacker to circumvent existing security protections. Exploitation of this weakness could enable unauthorized access to files or bypass intended security restrictions. The vulnerability has been patched in recent versions of both applications.

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

Quick answers

Is CVE-2026-109763 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-109763 being exploited in the wild.
How severe is CVE-2026-109763?: Informational severity, 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-2026-109763?: Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-109763 attacked?: It is in a web application.
Am I affected by CVE-2026-109763?: 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 153.5

Technical details

A mitigation bypass exists in the File Handling component of Firefox and Thunderbird. The vulnerability allows an attacker to circumvent existing security mitigations, potentially leading to unauthorized file access or other security violations. The fix has been deployed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

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

References

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