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.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alma_linux | — | Upgrade thunderbird | Jun 12, 2025 | May 14, 2025 |
| Amazon Linux Ami 2 | — | Upgrade thunderbirdUpgrade thunderbird-debuginfo | May 30, 2025 | May 14, 2025 |
| Debian | — | Upgrade thunderbird | May 20, 2025 | May 14, 2025 |
| Mozilla Thunderbird | — | Upgrade to Mozilla Thunderbird version 138.0.1Upgrade to the latest version of Mozilla Thunderbird | May 15, 2025 | May 13, 2025 |
| Oracle_linux | — | Upgrade thunderbird | May 29, 2025 | May 14, 2025 |
| Redhat_linux | — | Upgrade thunderbird-debuginfoUpgrade thunderbird-debugsourceNo solution existsUpgrade thunderbird | May 29, 2025 | May 14, 2025 |
| Rocky_linux | — | Upgrade thunderbird-debuginfoUpgrade thunderbird-debugsourceUpgrade thunderbird | Sep 9, 2025 | Jul 29, 2025 |
| Suse | — | Upgrade MozillaThunderbird-translations-commonUpgrade MozillaThunderbirdUpgrade MozillaThunderbird-translations-other | May 26, 2025 | May 14, 2025 |
| Ubuntu | — | Upgrade thunderbird | Jul 23, 2025 | May 14, 2025 |
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