CVE-2025-3909

Thunderbird's handling of the X-Mozilla-External-Attachment-URL header can be exploited to execute JavaScript in the file:/// context. By crafting a nested email attachment (message/rfc822) and setting its content type to application/pdf, Thunderbird may incorrectly render it as HTML when opened, allowing the embedded JavaScript to run without requiring a file download. This behavior relies on Thunderbird auto-saving the attachment to /tmp and linking to it via the file:/// protocol, potentially enabling JavaScript execution as part of the HTML. This vulnerability affects Thunderbird < 128.10.1 and Thunderbird < 138.0.1.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 2.5

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://bugzilla.mozilla.org/show_bug.cgi?id=1958376	Permissions Required
https://www.mozilla.org/security/advisories/mfsa2025-34/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-35/	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:mozilla:thunderbird::::::::
	cpe:2.3:a:mozilla:thunderbird::::::::

History

05 Jun 2025, 14:26

Type	Values Removed	Values Added
New CVE

Information

Published : 2025-05-14 17:15

Updated : 2025-06-05 14:26

NVD link : CVE-2025-3909

Mitre link : CVE-2025-3909

CVE.ORG link : CVE-2025-3909

JSON object : View

Products Affected

mozilla

thunderbird

CWE

CWE-290

Authentication Bypass by Spoofing

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