Jenkins Email Extension Plugin: file: URLs in inlined images read arbitrary controller files

Impact

The plugin inlines images referenced with a data-inline attribute as base64 without restricting the URL scheme, so an attacker who can influence email content can supply a file: URL and have the controller read any file it can reach and deliver it in the outgoing mail. On a build controller that means credentials.xml, SSH keys to the GPU fleet, kubeconfigs and registry tokens - the material that lets a CI system deploy to every node. The reader of the exfiltrated mail is whoever the job addresses, so the leak leaves the controller through a normal-looking notification. Affects Email Extension Plugin 1933.v45cec755423f and earlier.

Who can reach it

Any authenticated Jenkins user who can control email body content - that is, edit a job's extended email configuration or supply a template the job renders. No controller admin rights are needed.

What to do

Update the Email Extension Plugin from the Jenkins update center to a release later than 1933.v45cec755423f; the Jenkins security advisory for 2026-05-27 (SECURITY-3705) carries the fixed version. A plugin update requires a controller restart to take effect, which drains and interrupts running builds but touches no GPU node. Treat any secret readable by the controller as potentially exposed if untrusted users held job-configure rights, and rotate.

References

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