CVE-2025-3909
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.
How to fix
- mozilla thunderbird128.10.1, 138.0.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla thunderbird | v < 128.10.1, 129.0 ≤ v < 138.0.1 | 128.10.1, 138.0.1 |
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