CVE-2025-59419: Netty netty-codec-smtp SMTP Command Injection Vulnerability Allowing Email Forgery

Vulnerability summary

CVE-2025-59419 is a medium (CVSS 5.5) vulnerability in netty. EPSS estimates a 1.55% chance of exploitation in the next 30 days, higher than 75.1% of scored vulnerabilities.

Timeline

1. 15-10-2025
   PublishedVulnerability first disclosed.
2. 17-10-2025
   Last modifiedVulnerability information updated.

Description

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.

• CWE-93Improper Neutralization of CRLF SequencesThe product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.