CVE-2006-0631 in mailback
Summary
by MITRE
CRLF injection vulnerability in mailback.pl in Erik C. Thauvin mailback allows remote attackers to use mailback as a "spam proxy" by modifying mail headers, including recipient e-mail addresses, via newline characters in the Subject field.
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Analysis
by VulDB Data Team • 08/04/2017
The CVE-2006-0631 vulnerability represents a critical CRLF injection flaw in the mailback.pl script developed by Erik C. Thauvin, which fundamentally compromises email security mechanisms and enables malicious actors to exploit the system for unauthorized spam distribution. This vulnerability specifically targets the mailback.pl utility, which is designed to send email responses to users who submit forms or messages, making it a potential vector for large-scale spam operations. The flaw occurs when the script fails to properly sanitize user input, particularly in the Subject field, allowing attackers to inject carriage return and line feed characters that manipulate the email header structure.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the mailback.pl script, which directly processes user-supplied data without proper encoding or filtering of special characters. When an attacker submits a form with newline characters in the Subject field, these characters are interpreted as CRLF (Carriage Return Line Feed) sequences that break out of the intended email header context. This allows attackers to inject arbitrary email headers including recipient addresses, sender information, and other header fields, effectively transforming the legitimate mailback script into an unauthorized spam relay mechanism.
The operational impact of this vulnerability extends beyond simple email manipulation, as it enables attackers to use compromised systems as spam proxies, potentially leading to reputation damage for affected organizations and facilitating large-scale phishing campaigns. The vulnerability operates at the application layer and can be exploited remotely without requiring authentication, making it particularly dangerous for web applications that process user input through email functions. This type of vulnerability aligns with CWE-113, which specifically addresses "Improper Neutralization of CRLF Sequences in HTTP Headers" and falls under the broader category of injection flaws that compromise application security.
Security implications of CVE-2006-0631 are significant as they allow for unauthorized email relay operations that can bypass spam filters and email server security measures. The vulnerability enables attackers to manipulate email routing and delivery, potentially leading to spam distribution across multiple networks and domains. Organizations using affected mailback.pl implementations face risks of being blacklisted by email providers and experiencing email deliverability issues. The attack vector operates through standard web forms, making it accessible to attackers with basic knowledge of email header manipulation techniques and demonstrating the importance of proper input validation in web applications.
Mitigation strategies for this vulnerability should include immediate input sanitization of all user-supplied data, particularly in email-related fields, and implementation of proper encoding for special characters including carriage return and line feed sequences. Security measures must enforce strict validation of email headers and reject any input containing CRLF sequences in critical header fields. Organizations should also implement proper logging and monitoring of email submission activities to detect anomalous patterns that may indicate exploitation attempts. The remediation process involves updating the mailback.pl script to properly escape or remove special characters from user input before processing, ensuring that header fields cannot be manipulated through malicious input injection, which aligns with ATT&CK technique T1190 for gaining access through exploitation of vulnerabilities.