CVE-2015-9097 in Mail gem
Summary
by MITRE
The mail gem before 2.5.5 for Ruby (aka A Really Ruby Mail Library) is vulnerable to SMTP command injection via CRLF sequences in a RCPT TO or MAIL FROM command, as demonstrated by CRLF sequences immediately before and after a DATA substring.
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Analysis
by VulDB Data Team • 12/08/2022
The CVE-2015-9097 vulnerability represents a critical SMTP command injection flaw in the mail gem version 2.5.4 and earlier for Ruby applications. This vulnerability specifically targets the mail gem's handling of email command sequences, particularly in the RCPT TO and MAIL FROM commands where CRLF (Carriage Return Line Feed) sequences can be exploited to manipulate SMTP protocol execution. The vulnerability arises from insufficient input validation and sanitization of email address parameters that are processed through SMTP commands, creating a pathway for malicious actors to inject arbitrary SMTP commands into the email transmission process.
The technical exploitation of this vulnerability occurs when CRLF sequences are embedded immediately before and after a DATA substring within email address parameters. This manipulation allows attackers to inject additional SMTP commands that would normally be restricted or properly escaped, effectively bypassing the intended protocol boundaries. The flaw stems from the mail gem's improper handling of special characters in email address validation, where the application fails to properly sanitize input before constructing SMTP commands. This weakness directly relates to CWE-77 and CWE-78, which address command injection vulnerabilities in software systems. The vulnerability enables attackers to potentially execute unauthorized SMTP commands such as DATA, RSET, or other protocol instructions that could lead to email spoofing, relay abuse, or even server compromise.
The operational impact of CVE-2015-9097 extends beyond simple command injection, potentially allowing attackers to manipulate email routing, bypass authentication mechanisms, or gain unauthorized access to email servers. Applications using vulnerable versions of the mail gem may become susceptible to email relay attacks where malicious users can inject commands to redirect emails, access server resources, or perform unauthorized operations. This vulnerability particularly affects Ruby applications that process email addresses through SMTP protocols, including web applications, email services, and automated notification systems. The attack vector is particularly concerning because it can be exploited through seemingly legitimate email address inputs, making detection and prevention more challenging. The vulnerability also aligns with ATT&CK technique T1190 for exploitation of remote services and T1071.004 for application layer protocol usage, as it exploits SMTP protocol weaknesses in Ruby email handling libraries.
Organizations utilizing affected versions of the mail gem should immediately implement mitigations including upgrading to version 2.5.5 or later, which includes proper input sanitization and CRLF sequence validation. Additional protective measures involve implementing strict email address validation routines that filter out special characters, employing SMTP command whitelisting mechanisms, and monitoring email server logs for unusual command sequences. Security teams should also consider implementing network-level restrictions on SMTP relay access and conducting thorough code reviews to identify other potential injection points in email processing components. The vulnerability demonstrates the importance of proper input validation in network protocol implementations and highlights how seemingly minor flaws in string handling can lead to significant security compromises. Organizations should also consider implementing automated vulnerability scanning tools that can detect the presence of vulnerable mail gem versions in their application environments and ensure comprehensive patch management processes are in place to address such vulnerabilities promptly.