CVE-2025-3909
JavaScript Execution via Spoofed PDF Attachment and file:/// Link
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.
| Vendor | mozilla |
| Product | thunderbird |
| Ecosystems | |
| Industries | Technology |
| Published | May 14, 2025 |
| Last Updated | Apr 13, 2026 |
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