Executive brief
Nodemailer is a Node.js library that sends emails on behalf of applications. A parsing flaw in versions 9.1.0 through 10.0.8 allows attackers to inject malformed recipient addresses by exploiting RFC 5322 comment syntax, potentially causing emails to be sent to unintended recipients or triggering unexpected behavior in SMTP server processing.
Technical details
The address parser fails to properly sanitize quoted local-parts followed by RFC 5322 comments, retaining attacker-controlled domain fragments in the normalized address (e.g., "user"@example.com(x)evil.com becomes user@example.com evil.com). This malformed address is propagated directly into the SMTP envelope without additional validation. Network-based attacker with no privileges required can supply crafted email addresses; confirmed impact is malformed recipient acceptance, though end-to-end SMTP delivery impact is not yet confirmed.
Affected products
- Nodemailer Project Nodemailer >=9.1.0, <10.0.9
Timeline
- 2026-09-26: disclosed
- 2026-09-26: patched: Version 10.0.9 contains the fix