Vulnerability · NVD

CVE-2025-3909

HIGH 8.1 Published on 2025-05-14

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.

Attack vector : Network No privileges required

Show raw CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS 0.41% exploit very unlikely percentile 33.7%

Tracked apps referencing this CVE

For each app: the affected range, the fixing version, and where the tracked app stands today.

Mozilla Thunderbird Windows winget:Mozilla.Thunderbird

Affected ≥129.0 <138.0.1 Fixed in 138.0.1 Latest tracked 153.0.2 patched

Vulnerable CPE configurations (2)

Vendor	Product	Platform	Versions	CPE 2.3 URI
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	<128.10.1	cpe:2.3:a:mozilla:thunderbird::::::::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	≥129.0 <138.0.1	cpe:2.3:a:mozilla:thunderbird::::::::

View on NVD ↗ Advisory · www.mozilla.org