CVE-2025-3909
Publication date 14 May 2025
Last updated 27 February 2026
Ubuntu priority
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 affects Thunderbird < 128.10.1 and Thunderbird < 138.0.1.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| thunderbird | ||
| 24.04 LTS noble |
Not affected
|
|
| 22.04 LTS jammy |
Fixed 1:128.12.0+build1-0ubuntu0.22.04.1
|
|
| 20.04 LTS focal | Not in release |
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
8.1 · High
|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | Required |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity impact | High |
| Availability impact | None |
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N |
References
Related Ubuntu Security Notices (USN)
- USN-7663-1
- Thunderbird vulnerabilities
- 22 July 2025