CVE-2026-8959
Firefox Widget Win32 Sandbox Escape Vulnerability
Publication date: 2026-05-19
Last updated on: 2026-05-20
Assigner: Mozilla Corporation
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| 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 ID | Description |
|---|---|
| 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. |
| 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. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
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.
How can this vulnerability impact me? :
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.
What immediate steps should I take to mitigate this vulnerability?
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.