CVE-2026-84640

Analyzed Analyzed - Analysis Complete

Thunderbird Memory Corruption via Malicious Mail Header

Publication date: 2026-09-01

Last updated on: 2026-09-03

Assigner: Mozilla Corporation

Description

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-01

Last Modified

2026-09-03

Generated

2026-09-22

AI Q&A

2026-09-02

EPSS Evaluated

2026-09-20

NVD

CVE-2026-84640

EUVD

EUVD-2026-69709

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-126	The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

Attack-Flow Graph

Executive Summary

This vulnerability involves a maliciously crafted mail header that causes a one byte read past the end of a buffer in Thunderbird. This could potentially lead to memory corruption or crashes.

Detection Guidance

This vulnerability is specific to Thunderbird versions before 155, 140.15, and 153.2. Detection involves checking installed Thunderbird versions. Use commands like 'thunderbird --version' or check package managers (e.g., 'dpkg -l | grep thunderbird' for Debian/Ubuntu). If outdated, update immediately.

Impact Analysis

An attacker could exploit this to cause Thunderbird to crash or potentially execute arbitrary code, leading to data loss or unauthorized access to your system.

Compliance Impact

This vulnerability involves a one-byte buffer overflow in mail headers, which could potentially lead to memory corruption or crashes. However, the provided CVE data does not specify any direct impact on compliance with standards like GDPR or HIPAA. Such impacts would depend on the specific system configuration and data processing environment.

Mitigation Strategies

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

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