CVE-2026-100804

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Use-After-Free Sandbox Escape in Firefox

Publication date: 2026-09-29

Last updated on: 2026-09-30

Assigner: Mozilla Corporation

Description

Sandbox escape due to use-after-free in the Preferences: Backend component. This vulnerability was fixed in Thunderbird 157 and Firefox 157.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-29

Last Modified

2026-09-30

Generated

2026-10-19

AI Q&A

2026-09-29

EPSS Evaluated

2026-10-18

NVD

CVE-2026-100804

EUVD

EUVD-2026-88957

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	157

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-416	The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Attack-Flow Graph

Executive Summary

This vulnerability is a sandbox escape caused by a use-after-free bug in Firefox's Preferences Backend component. A use-after-free occurs when a program tries to use memory that has already been freed, potentially allowing an attacker to execute arbitrary code or escape the browser sandbox.

Detection Guidance

This vulnerability is specific to Firefox versions before 157. To detect it, check your Firefox version using about:support in the browser or run firefox --version in the terminal. If the version is below 157, the system is vulnerable.

Impact Analysis

This vulnerability could allow an attacker to break out of the browser sandbox and execute malicious code on your system. If exploited, it may lead to unauthorized access to sensitive data, installation of malware, or further compromise of your device.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR or HIPAA by enabling unauthorized code execution or data exfiltration due to sandbox escape. A successful exploit may allow attackers to bypass security controls, leading to data breaches or unauthorized access to sensitive information.

Mitigation Strategies

Update Firefox to version 157 or later immediately. Disable automatic updates temporarily if needed, but prioritize patching. Avoid using untrusted extensions or websites until updated.

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