{"id":"CVE-2025-3909","details":"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 affects Thunderbird \u003c 128.10.1 and Thunderbird \u003c 138.0.1.","modified":"2026-04-16T04:36:32.131601073Z","published":"2025-05-14T17:15:48.660Z","related":["ALSA-2025:8196","ALSA-2025:8756","SUSE-SU-2025:01660-1","SUSE-SU-2025:01660-2","openSUSE-SU-2025:15131-1"],"references":[{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/05/msg00022.html"},{"type":"ADVISORY","url":"https://www.mozilla.org/security/advisories/mfsa2025-34/"},{"type":"ADVISORY","url":"https://www.mozilla.org/security/advisories/mfsa2025-35/"},{"type":"REPORT","url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1958376"}],"affected":[{"database_specific":{"unresolved_ranges":[{"events":[{"introduced":"0"},{"fixed":"128.10.1"}]},{"events":[{"introduced":"129.0"},{"fixed":"138.0.1"}]}],"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-3909.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N"}]}