CVE-2004-1643 in WS_FTP Server
Summary
by MITRE
WS_FTP 5.0.2 allows remote authenticated users to cause a denial of service (CPU consumption) via a CD command that contains an invalid path with a "../" sequence.
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Analysis
by VulDB Data Team • 07/14/2025
The vulnerability identified as CVE-2004-1643 affects WS_FTP 5.0.2, a widely used file transfer protocol client and server software that was prevalent in enterprise environments during the early 2000s. This particular flaw represents a classic denial of service vulnerability that exploits improper input validation mechanisms within the application's handling of file path navigation commands. The issue specifically manifests when a remote authenticated user submits a CD command containing an invalid path with a "../" sequence, which triggers excessive CPU consumption and ultimately leads to system resource exhaustion.
The technical root cause of this vulnerability lies in the application's inadequate path validation and traversal handling mechanisms. When the WS_FTP server receives a CD command with a malformed path containing the "../" sequence, it fails to properly sanitize or validate the input before processing. This allows the application to enter into an infinite loop or excessive recursive path resolution process, consuming CPU cycles continuously. The vulnerability is classified under CWE-20 as "Improper Input Validation" and specifically relates to CWE-22 "Path Traversal" in its exploitation methodology. The flaw demonstrates poor error handling and lacks proper bounds checking when processing directory navigation commands, creating an exploitable condition that can be triggered remotely by authenticated users.
From an operational perspective, this vulnerability poses significant risks to organizations relying on WS_FTP for their file transfer operations. The denial of service condition can render the FTP service completely unavailable to legitimate users, disrupting business operations and potentially causing financial losses. Attackers can exploit this vulnerability with minimal privileges required for authentication, making it particularly dangerous in environments where multiple users have access to the FTP service. The continuous CPU consumption can also affect system performance, potentially causing cascading failures in network infrastructure and other dependent services. This vulnerability aligns with ATT&CK technique T1499.004 "Endpoint Denial of Service" and represents a common exploitation pattern that demonstrates how seemingly benign path traversal commands can be weaponized to compromise system availability.
The mitigation strategies for this vulnerability should include immediate application of vendor patches or updates that address the input validation flaws in WS_FTP 5.0.2. Organizations should also implement network segmentation to limit access to FTP services and enforce strict authentication controls to minimize the attack surface. Additional protective measures include implementing rate limiting on FTP commands, monitoring for unusual CPU consumption patterns, and establishing proper input sanitization procedures. System administrators should consider upgrading to more modern FTP solutions that have robust input validation and security features, as WS_FTP 5.0.2 represents an outdated platform with known security limitations. The vulnerability serves as a reminder of the importance of proper input validation and error handling in network services, particularly those handling user-supplied data that could be manipulated to cause system instability. Organizations should also conduct regular security assessments to identify similar validation flaws in other network applications and implement comprehensive monitoring solutions to detect and respond to denial of service attacks.