CVE-2026-103500

Modified Modified - Updated After Analysis

Heap Buffer Overflow in Thunderbird Email Client

Publication date: 2026-09-30

Last updated on: 2026-10-16

Assigner: Mozilla Corporation

Description

An attacker could cause a heap buffer overflow by getting a user to open an email that is greater than or equal to 2GB in size. This vulnerability was fixed in Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-30

Last Modified

2026-10-16

Generated

2026-10-19

AI Q&A

2026-09-30

EPSS Evaluated

2026-10-18

NVD

CVE-2026-103500

EUVD

EUVD-2026-90200

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	thunderbird	From 154.0 (inc) to 157.0 (exc)
mozilla	thunderbird	to 140.17.0 (exc)
mozilla	thunderbird	From 141.0 (inc) to 153.4.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-122	A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
CWE-787	The product writes data past the end, or before the beginning, of the intended buffer.

Attack-Flow Graph

Executive Summary

This vulnerability allows an attacker to cause a heap buffer overflow by tricking a user into opening an email larger than or equal to 2GB. This flaw was fixed in Thunderbird versions 157, 140.17, and 153.4.

Detection Guidance

This vulnerability involves a heap buffer overflow triggered by opening an email larger than or equal to 2GB. Detection would require monitoring for abnormal memory usage or crashes when handling large files in Thunderbird. Check Thunderbird version with 'thunderbird --version' and compare against fixed versions (157, 140.17, 153.4).

Inspect system logs for Thunderbird crashes or memory errors during email processing. No specific commands are provided in the context for direct detection.

Impact Analysis

An attacker could exploit this to crash the application, corrupt data, or potentially execute arbitrary code on your system by sending a very large email. Opening such an email triggers the buffer overflow.

Compliance Impact

This vulnerability does not directly impact compliance with GDPR, HIPAA, or similar standards as it involves a heap buffer overflow triggered by opening a large email, which is not a common compliance violation scenario. Compliance risks typically arise from data breaches or unauthorized access, which are not described in this CVE.

Mitigation Strategies

Update Thunderbird to version 157, 140.17, or 153.4 immediately. Avoid opening emails larger than 2GB until patched. Disable automatic email loading if possible to reduce exposure.

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