CVE-2001-0688 in Broker FTP Server
Summary
by MITRE
Broker FTP Server 5.9.5.0 allows a remote attacker to cause a denial of service by repeatedly issuing an invalid CD or CWD ("CD . .") command.
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability identified as CVE-2001-0688 affects the Broker FTP Server version 5.9.5.0 and represents a classic denial of service flaw that exploits improper handling of malformed directory change commands. This vulnerability resides within the file transfer protocol implementation where the server fails to properly validate and process certain command sequences, specifically targeting the CD (change directory) and CWD (change working directory) commands with invalid parameters. The flaw manifests when an attacker repeatedly sends malformed CD or CWD commands containing sequences such as "CD . ." which contain consecutive dots separated by spaces, creating an invalid path specification that the server cannot properly process.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the FTP server's command processing logic. When the Broker FTP Server receives these malformed commands, it fails to properly sanitize the input or implement appropriate bounds checking mechanisms. This results in the server entering an infinite loop or consuming excessive system resources while attempting to process the invalid command sequences. The repeated nature of the attack means that an attacker can continuously send these malformed commands without requiring authentication, making the vulnerability particularly dangerous in unsecured network environments where FTP servers are accessible to external parties.
From an operational impact perspective, this vulnerability creates significant security implications for organizations relying on Broker FTP Server implementations. The denial of service condition effectively renders the FTP service unavailable to legitimate users, potentially disrupting business operations and file transfer capabilities. The attack requires minimal resources from the attacker's side, as it only involves sending simple malformed commands over the network, making it an attractive vector for malicious actors seeking to disrupt services. Organizations may experience extended downtime while administrators investigate and implement fixes, potentially affecting critical data exchange operations and user productivity. The vulnerability also highlights the importance of proper input validation in network services, as the flaw exists in the fundamental command processing layer of the FTP server implementation.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a specific instance of CWE-121, concerning buffer overflow conditions. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service attacks, specifically targeting the availability aspect of the CIA triad. The attack vector requires network access to the FTP service port, typically TCP 21, and can be executed from any external location without requiring prior authentication credentials. Organizations should implement immediate mitigations including applying vendor patches, configuring firewalls to restrict FTP service access, and implementing rate limiting mechanisms to prevent excessive command processing. Additionally, network monitoring should be enhanced to detect unusual command patterns that may indicate exploitation attempts, while regular security assessments should verify that similar vulnerabilities do not exist in other network services or applications within the organization's infrastructure.