CVE-2026-84639

Analyzed Analyzed - Analysis Complete

Thunderbird Memory Corruption in MIME Handling

Publication date: 2026-09-01

Last updated on: 2026-09-03

Assigner: Mozilla Corporation

Description

Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-01

Last Modified

2026-09-03

Generated

2026-09-05

AI Q&A

2026-09-02

EPSS Evaluated

2026-09-03

NVD

CVE-2026-84639

EUVD

EUVD-2026-69708

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	thunderbird	From 154.0 (inc) to 155.0 (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-457	The code uses a variable that has not been initialized, leading to unpredictable or unintended results.

Attack-Flow Graph

Executive Summary

This vulnerability involves Thunderbird incorrectly using uninitialized memory when certain MIME bodies trigger an error condition. This flaw was addressed in specific Thunderbird versions.

Detection Guidance

This vulnerability is specific to Thunderbird versions before 155, 140.15, and 153.2. Detection involves checking the installed Thunderbird version. Use commands like 'thunderbird --version' or check package managers (e.g., 'apt list --installed | grep thunderbird' for Debian/Ubuntu). If the version is below the patched releases, the system is vulnerable.

Impact Analysis

An attacker could exploit this to read sensitive data from memory or cause unexpected behavior in Thunderbird. Users running vulnerable versions may be at risk of information disclosure.

Compliance Impact

This vulnerability could lead to unauthorized data access, potentially violating GDPR (data protection) or HIPAA (health data privacy) if sensitive information is exposed.

Mitigation Strategies

Update Thunderbird to version 155, 140.15, or 153.2 or later to address the vulnerability.

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