CVE-2026-84143

Modified Modified - Updated After Analysis

Memory Corruption Vulnerability in Firefox

Publication date: 2026-09-01

Last updated on: 2026-09-03

Assigner: Mozilla Corporation

Description

Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-09-01

Last Modified

2026-09-03

Generated

2026-09-21

AI Q&A

2026-09-01

EPSS Evaluated

2026-09-20

NVD

CVE-2026-84143

EUVD

EUVD-2026-69091

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	From 154.0.0 (inc) to 155.0.0 (exc)
mozilla	thunderbird	From 154.0 (inc) to 155.0 (exc)
mozilla	firefox	to 140.15.0 (exc)
mozilla	firefox	From 141.0.0 (inc) to 153.2.0 (exc)
mozilla	thunderbird	to 140.15.0 (exc)
mozilla	thunderbird	From 141.0 (inc) to 153.2.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-200	The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
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.

Attack-Flow Graph

Executive Summary

This vulnerability involves multiple internally found bugs in Firefox versions 154, ESR 153.1, and ESR 140.14. Some of these bugs could lead to memory corruption or other security issues, potentially allowing exploitation with sufficient effort. The issue was addressed in later versions: Firefox 155, ESR 140.15, and ESR 153.2.

Detection Guidance

Detection requires checking Firefox version against vulnerable releases. Use commands like 'firefox --version' or check installed package versions via system package managers (e.g., 'apt list --installed | grep firefox' on Debian/Ubuntu). Compare versions to Firefox 154, ESR 153.1, or ESR 140.14.

Impact Analysis

If exploited, this vulnerability could allow attackers to execute arbitrary code, gain unauthorized access, or cause system crashes. Users running affected Firefox versions may be at risk of data breaches or malware infections.

Compliance Impact

The provided CVE data does not specify how this vulnerability affects compliance with standards like GDPR or HIPAA. The description only mentions memory corruption or security defects in Firefox versions, without details on potential data exposure or regulatory impacts.

Mitigation Strategies

Upgrade Firefox to version 155 or later, Firefox ESR 140.15 or later, or Firefox ESR 153.2 or later. Disable automatic updates temporarily if needed, but prioritize patching to address potential memory corruption risks.

Hi! I’m here to help you understand CVE-2026-84143. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70