CVE-2025-3909
JavaScript Execution via Spoofed PDF Attachment and file:/// Link
- State
- Published
- Severity
- 8.1 High
- Published
- May 14, 2025
- Updated
- Apr 13, 2026
- Reserved
- Apr 23, 2025
Description
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 was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 8.1 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N | CISA-ADP |
Weaknesses
- CWE-356 Product UI does not Warn User of Unsafe Actions
Affected Products
| Product | Versions |
|---|---|
ThunderbirdMozilla |
|
References
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