When a call-site passes a subject for an email that contains line-breaks in Apache Commons Email 1.0 through 1.4, the caller can add arbitrary SMTP headers.

If a user of Apache Commons Email (typically an application programmer) passes unvalidated input as the so-called "Bounce Address", and that input contains line-breaks, then the email details (recipients, contents, etc.) might be manipulated. Mitigation: Users should upgrade to Commons-Email 1.5. You can mitigate this vulnerability for older versions of Commons Email by stripping line-breaks from data, that will be passed to Email.setBounceAddress(String).