CVE-2004-1602 in ProFTPD
Summary
by MITRE
ProFTPD 1.2.x, including 1.2.8 and 1.2.10, responds in a different amount of time when a given username exists, which allows remote attackers to identify valid usernames by timing the server response.
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Analysis
by VulDB Data Team • 07/06/2025
This vulnerability in ProFTPD versions 1.2.x, specifically affecting 1.2.8 and 1.2.10, represents a classic timing attack scenario that exploits inconsistent response times to infer system information. The flaw stems from the server's differential handling of authentication attempts based on whether a username exists in the system, creating measurable time variations that can be exploited by remote attackers. This type of vulnerability falls under the category of information disclosure through timing side channels, where the attacker can determine the validity of usernames by analyzing response delays during authentication attempts.
The technical implementation of this vulnerability occurs at the authentication layer where ProFTPD's handling of user credentials varies significantly between valid and invalid username attempts. When a username exists in the system, the server performs additional lookup operations and processing steps that result in longer response times compared to when an invalid username is provided. This timing difference, though subtle, becomes measurable over multiple attempts and can be amplified through statistical analysis to definitively identify valid usernames within the system's user base.
From an operational impact perspective, this vulnerability creates a significant risk for systems running affected ProFTPD versions as it enables credential stuffing attacks and brute force attempts with much higher success rates. Attackers can systematically test usernames against the server, using the timing variations to quickly identify valid accounts without requiring knowledge of passwords. This weakness undermines the fundamental security principle of authentication systems where the response should remain constant regardless of whether credentials are valid or invalid, as outlined in the principle of constant-time execution.
The vulnerability aligns with several cybersecurity frameworks and standards, including CWE-203 which addresses "Information Disclosure Through Timing Variations" and reflects the broader category of side-channel attacks that have been increasingly targeted in modern security assessments. From an ATT&CK framework perspective, this vulnerability maps to T1110.001 - "Brute Force: Password Guessing" and T1562.001 - "Impair Defenses: Disable or Modify Tools" as it enables attackers to more effectively target authentication systems. The timing-based nature of this flaw also connects to the broader category of timing attacks that have been documented in various network protocols and authentication systems, making it a well-understood but persistent threat vector.
Organizations should immediately upgrade to ProFTPD versions that address this timing inconsistency, typically those beyond 1.2.11, as the fix involves implementing consistent response times regardless of username validity. Additional mitigations include implementing account lockout mechanisms, rate limiting for authentication attempts, and employing more robust authentication methods such as two-factor authentication. Network segmentation and monitoring for unusual authentication patterns can also help detect exploitation attempts, while regular security assessments should include testing for timing variations in authentication systems to prevent similar vulnerabilities from emerging in other services.