Netty netty-codec-smtp SMTP Command Injection Vulnerability Allowing Email Forgery

Summary

Netty is an asynchronous, event-driven network application framework. In versions prior to 4.1.128.Final and 4.2.7.Final, the SMTP codec in Netty contains an SMTP command injection vulnerability due to insufficient input validation for Carriage Return (\r) and Line Feed (\n) characters in user-supplied parameters. The vulnerability exists in io.netty.handler.codec.smtp.DefaultSmtpRequest, where parameters are directly concatenated into the SMTP command string without sanitization. When methods such as SmtpRequests.rcpt(recipient) are called with a malicious string containing CRLF sequences, attackers can inject arbitrary SMTP commands. Because the injected commands are sent from the server's trusted IP address, resulting emails will likely pass SPF and DKIM authentication checks, making them appear legitimate. This allows remote attackers who can control SMTP command parameters (such as email recipients) to forge arbitrary emails from the trusted server, potentially impersonating executives and forging high-stakes corporate communications. This issue has been patched in versions 4.1.129.Final and 4.2.8.Final. No known workarounds exist.

Timeline

1. Oct 15, 2025, 3:42 PM UTCCVE published
2. Oct 15, 2025, 5:21 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: partial

3. Oct 17, 2025, 7:44 PM UTCRecord last updated

Affected versions

• netty netty

  fixed in 4.2.7.Final; From 4.2.0.Alpha1 · fixed in 4.1.128.Final

• io.netty:netty-codec-smtpMaven

  From 4.2.0.Alpha1 · fixed in 4.2.7.Final

• io.netty:netty-codec-smtpMaven

  fixed in 4.1.128.Final

References 2