CVE-2026-84118

Analyzed Analyzed - Analysis Complete

Use-After-Free in Firefox JavaScript GC

Publication date: 2026-09-01

Last updated on: 2026-09-02

Assigner: Mozilla Corporation

Description

Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-01

Last Modified

2026-09-02

Generated

2026-09-22

AI Q&A

2026-09-01

EPSS Evaluated

2026-09-20

NVD

CVE-2026-84118

EUVD

EUVD-2026-69070

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	to 153.2.0 (exc)
mozilla	firefox	From 154.0.0 (inc) to 155.0.0 (exc)
mozilla	thunderbird	to 153.2.0 (exc)
mozilla	thunderbird	From 154.0 (inc) to 155.0 (exc)

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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.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

CVE-2026-84118 is a use-after-free vulnerability in Firefox's JavaScript garbage collection component. This flaw occurs when the program attempts to use memory that has already been freed, potentially leading to memory corruption or arbitrary code execution.

Detection Guidance

Detecting this vulnerability requires checking the installed version of Firefox or Firefox ESR. On Linux or macOS, run: firefox --version or firefox-esr --version. On Windows, check the application properties. If the version is below 155 for Firefox or 153.2 for ESR, the system is vulnerable.

Impact Analysis

Attackers could exploit this vulnerability to execute malicious code, crash the browser, or gain unauthorized access to your system. Successful exploitation may allow them to install malware, steal data, or take control of your device.

Compliance Impact

This vulnerability could lead to data breaches, which may violate GDPR's data protection requirements or HIPAA's safeguards for protected health information. Organizations using vulnerable Firefox versions may face compliance penalties and reputational damage.

Mitigation Strategies

Immediately update Firefox to version 155 or Firefox ESR to version 153.2. Disable JavaScript if updates are not possible, as this vulnerability is tied to the JavaScript: GC component. Monitor for unusual system behavior or crashes that may indicate exploitation attempts.

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