CVE-2026-8959
Analyzed Analyzed - Analysis Complete
Firefox Widget Win32 Sandbox Escape Vulnerability

Publication date: 2026-05-19

Last updated on: 2026-05-20

Assigner: Mozilla Corporation

Description
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
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Meta Information
Published
2026-05-19
Last Modified
2026-05-20
Generated
2026-06-10
AI Q&A
2026-05-19
EPSS Evaluated
2026-06-08
NVD
CVE-2026-8959
EUVD
EUVD-2026-30910
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
mozilla firefox to 151.0.0 (exc)
mozilla firefox to 140.11.0 (exc)
mozilla thunderbird to 151.0.0 (exc)
mozilla thunderbird to 140.11 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-693 The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
CWE-20 The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
CWE-119 The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
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Executive Summary

This vulnerability is a sandbox escape caused by incorrect boundary conditions in the Widget: Win32 component of Mozilla Firefox. Essentially, it allows an attacker to break out of the restricted environment (sandbox) that is designed to isolate processes, potentially gaining unauthorized access to the system.

The issue was addressed and fixed in Firefox version 151 and Firefox ESR 140.11.

Impact Analysis

By exploiting this vulnerability, an attacker could escape the sandbox environment, which is intended to limit the capabilities of potentially malicious code. This could lead to unauthorized access to system resources, execution of arbitrary code, or other malicious activities beyond the browser's normal restrictions.

Mitigation Strategies

To mitigate this vulnerability, update Firefox to version 151 or later, or Firefox ESR to version 140.11 or later, where the issue has been fixed.

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