Vulnerability · Published May 14, 2025 · Assigned by mozilla
CVE-2025-3909JavaScript Execution via Spoofed PDF Attachment and file:/// Link
High 8.1
In plain English
A high-severity security flaw in Thunderbird from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | thunderbird | 128.10.1-1.el10_0.alma.1 | ALSA-2025:8196 |
| AlmaLinux:8 | thunderbird | 128.11.0-1.el8_10.alma.1 | ALSA-2025:8756 |
| Debian:12 | thunderbird | 1:128.10.1esr-1~deb12u1 | DSA-5921-1 |
| Debian:12 | thunderbird | 1:128.10.1esr-1~deb12u1 | DEBIAN-CVE-2025-3909 |
| Debian:13 | thunderbird | 1:128.10.1esr-1 | DEBIAN-CVE-2025-3909 |
| Debian:14 | thunderbird | 1:128.10.1esr-1 | DEBIAN-CVE-2025-3909 |
| Rocky Linux:10 | thunderbird | 0:128.10.1-1.el10_0 | RLSA-2025:8196 |
| Rocky Linux:8 | thunderbird | 0:128.11.0-1.el8_10 | RLSA-2025:8756 |
| Rocky Linux:9 | thunderbird | 0:128.10.1-1.el9_6 | RLSA-2025:8203 |
| Ubuntu:22.04:LTS | thunderbird | 1:128.12.0+build1-0ubuntu0.22.04.1 | UBUNTU-CVE-2025-3909 |
| Ubuntu:22.04:LTS | thunderbird | 1:128.12.0+build1-0ubuntu0.22.04.1 | USN-7663-1 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-356 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N