CVE-2026-84637

Analyzed Analyzed - Analysis Complete

Thunderbird File URI Attachment Bypass Vulnerability

Publication date: 2026-09-01

Last updated on: 2026-09-03

Assigner: Mozilla Corporation

Description

Malicious calendar invitations could use file URI attachments to launch local or network-hosted executables on Windows, bypassing Thunderbird's normal executable attachment protections. With the new invitation display enabled, the attachment could also appear under a misleading filename. This vulnerability was fixed in Thunderbird 154 and Thunderbird 153.2.

CVSS Scores

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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-2026-84637

EUVD

EUVD-2026-69703

Affected Vendors & Products

Vendor	Product	Version / Range
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-434	The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.

Attack-Flow Graph

Executive Summary

This vulnerability involves malicious calendar invitations that use file URI attachments to execute local or network-hosted executables on Windows systems. It bypasses Thunderbird's normal protections against executable attachments. The issue was fixed in Thunderbird versions 154 and 153.2.

Detection Guidance

This vulnerability involves malicious calendar invitations with file URI attachments exploiting Thunderbird's executable handling. To detect it, inspect Thunderbird's attachment handling logs for unexpected executable launches or misleading filenames. Check for Thunderbird versions below 154 or 153.2, as these are vulnerable. Monitor network traffic for unusual file URI requests from calendar invitations.

Impact Analysis

An attacker could send a crafted calendar invitation that, when opened, runs unauthorized executable files on your system. This could lead to malware installation, data theft, or further compromise of your device.

Compliance Impact

This vulnerability could potentially lead to unauthorized code execution via malicious calendar invitations, which may result in data breaches or unauthorized access to sensitive information. This could impact compliance with standards like GDPR (data protection) and HIPAA (healthcare data privacy) by increasing the risk of data exposure or loss.

Mitigation Strategies

Update Thunderbird to version 154 or 153.2 or later to address the vulnerability.

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