CVE-2000-1033 in Serv-U
Summary
by MITRE
Serv-U FTP Server allows remote attackers to bypass its anti-hammering feature by first logging on as a valid user (possibly anonymous) and then attempting to guess the passwords of other users.
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Analysis
by VulDB Data Team • 10/11/2025
The vulnerability identified as CVE-2000-1033 affects the Serv-U FTP Server software, representing a significant security weakness in authentication mechanisms that undermines the server's built-in protection against brute force attacks. This flaw resides in the server's anti-hammering feature, which is designed to prevent automated password guessing attempts by limiting login attempts from suspicious sources. The vulnerability stems from a fundamental design flaw where the system's access control logic fails to properly enforce rate limiting and authentication restrictions across different user accounts.
The technical implementation of this vulnerability allows remote attackers to circumvent the server's protective measures through a specific attack pattern that exploits the server's handling of legitimate user sessions. An attacker can first establish a valid connection to the FTP server using any legitimate user account, which could include anonymous access, and then proceed to systematically attempt password guesses against other user accounts. This approach works because the anti-hammering mechanism only monitors and limits login attempts from the same IP address or session context rather than across all account attempts within a single authenticated session.
The operational impact of this vulnerability extends beyond simple credential theft, as it enables attackers to perform targeted password guessing attacks that could compromise multiple user accounts within the same FTP server environment. This represents a critical weakness in the server's authentication architecture and can lead to unauthorized access to sensitive data, privilege escalation, and potential system compromise. The vulnerability particularly affects environments where FTP servers host critical business data or where multiple user accounts exist with varying levels of access permissions.
From a cybersecurity perspective, this vulnerability aligns with CWE-307, which addresses improper restriction of excessive authentication attempts, and demonstrates how inadequate session management can undermine security controls. The attack pattern described in CVE-2000-1033 corresponds to techniques categorized under the ATT&CK framework's credential access tactics, specifically targeting password guessing and brute force methods. Organizations utilizing Serv-U FTP Server software would be particularly vulnerable to this attack vector, as it effectively nullifies the server's built-in protection mechanisms and allows for prolonged unauthorized access attempts.
The mitigation strategies for this vulnerability should focus on implementing comprehensive authentication controls that address session-based limitations and enforce stricter rate limiting across all user account attempts. Network administrators should consider implementing additional security measures such as account lockout policies, IP-based restrictions, and enhanced monitoring of authentication attempts. Regular security assessments and updates to the FTP server software are essential to prevent exploitation of this and similar vulnerabilities that could compromise the integrity of file transfer operations and the broader network infrastructure.