Jenkins Email Extension Plugin 1933.v45cec755423f and earlier allows inlining images as `base64` in email content by setting the `data-inline` attribute, without restrictions on the image URLs that can be inlined, allowing attackers able to control the email content to specify `file:` URLs for images to read arbitrary files from the Jenkins controller filesystem.
https://www.jenkins.io/security/advisory/2026-05-27/#SECURITY-3705