CVE-2001-0631 in Firstclass
Summary
by MITRE
Centrinity First Class Internet Services 5.50 allows for the circumventing of the default 'spam' filters via the presence of '<@>' in the 'From:' field, which allows remote attackers to send spoofed email with the identity of local users.
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Analysis
by VulDB Data Team • 03/23/2026
The vulnerability described in CVE-2001-0631 represents a significant email security flaw within Centrinity First Class Internet Services version 5.50 that directly undermines the system's ability to prevent spam and email spoofing attacks. This weakness specifically targets the email filtering mechanisms that are designed to protect users from unwanted and potentially malicious email communications. The vulnerability exploits a fundamental flaw in how the system processes email headers, particularly the 'From:' field, which is a critical component in email authentication and validation processes. Email systems rely on proper header parsing to determine the legitimacy of incoming messages and to apply appropriate filtering rules based on sender identity.
The technical implementation of this vulnerability occurs when an attacker includes the '<>' sequence within the 'From:' field of an email message. This specific pattern allows the system to bypass the default spam filtering mechanisms that would normally block or flag suspicious messages. The '<>' construct essentially tricks the email filtering system into treating the message as if it originated from a legitimate local user rather than from an external malicious source. This bypass mechanism operates at the application layer where email filtering rules are evaluated, effectively rendering the spam protection measures ineffective. The flaw demonstrates a classic case of improper input validation where the system fails to properly sanitize or validate email header content before applying security policies.
The operational impact of this vulnerability extends beyond simple spam delivery, creating a serious security risk for organizations using this email service. Attackers can exploit this weakness to send spoofed emails that appear to originate from trusted local users, potentially leading to social engineering attacks, phishing attempts, and the spread of malware through seemingly legitimate email communications. The ability to circumvent spam filters means that malicious actors can overwhelm user inboxes with unwanted messages while maintaining the appearance of legitimate correspondence. This vulnerability particularly affects organizations that rely heavily on email-based communication and have limited additional email security measures in place beyond the default filtering provided by the Centrinity system.
Organizations affected by this vulnerability should immediately implement compensating controls to address the security gap until a proper patch can be deployed. The recommended mitigation strategy involves configuring additional email filtering rules that specifically target the '<@>' pattern in email headers, implementing more robust email authentication mechanisms such as SPF, DKIM, and DMARC, and conducting thorough security audits of all email processing components. The vulnerability aligns with CWE-20, which describes improper input validation in software systems, and represents a clear violation of the principle of least privilege in email security. From an attack perspective, this vulnerability would fall under the ATT&CK technique T1566 for social engineering attacks through email, specifically targeting the initial access phase of cyber attacks. The security implications of this vulnerability highlight the critical importance of proper email header validation and the necessity of layered security approaches that do not rely solely on single points of failure in spam filtering systems.