CVE-2025-3909

Severity CVSS v4.0:

Pending analysis

Type:

Unavailable / Other

Publication date:

14/05/2025

Last modified:

13/04/2026

Description

Thunderbird&#39;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 was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.

Impact

Vector 3.x

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N CVSS v3.1 Severity and Metrics:

Base Score: 8.10 HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): Required
Scope (S): Unchanged
Confidentiality (C): High
Integrity (I): High
Availability (A): None

Base Score 3.x

8.10

Severity 3.x

HIGH

Vulnerable products and versions

CPE	From	Up to
cpe:2.3:a:mozilla:thunderbird::::::::		128.10.1 (excluding)
cpe:2.3:a:mozilla:thunderbird::::::::	129.0 (including)	138.0.1 (excluding)

To consult the complete list of CPE names with products and versions, see this page

CVE-2025-3909

Description

Impact

Vulnerable products and versions

References to Advisories, Solutions, and Tools