Netty SMTP Command Injection Vulnerability Allowing Email Forgery

A command injection vulnerability has been identified in the SMTP codec of Netty, versions prior to 4.1.128.Final and 4.2.7.Final. The vulnerability arises from inadequate input validation of Carriage Return (\r) and Line Feed (\n) characters in user-supplied parameters. This flaw allows remote attackers to inject arbitrary SMTP commands into the command string, exploiting methods that handle SMTP parameters, such as email recipients. The injected commands are executed from the server's trusted IP address, enabling forged emails to bypass SPF and DKIM checks, making them appear legitimate. This vulnerability could be exploited to impersonate high-profile individuals and manipulate important corporate communications.

Impact

Exploitation of this vulnerability allows for SMTP command injection, enabling attackers to forge emails from a trusted server by injecting commands that bypass standard email authentication. This could be used to impersonate executives and manipulate high-stakes corporate communications.

Reproduction

The vulnerability can be reproduced by sending an SMTP command injection payload through a method that accepts user-controlled parameters, such as 'rcpt()' for email recipients. The injected payload, which includes CRLF sequences, will be executed as separate SMTP commands, bypassing authentication and allowing for email forgery.

Remediation

Users can upgrade to Netty versions 4.1.129.Final or 4.2.8.Final, where this vulnerability has been patched.