CVE-2006-6558 in FTP Server
Summary
by MITRE
Crob FTP Server 3.6.1 b.263 allows remote attackers to cause a denial of service via a long series of "?A" sequences in the (1) LIST and possibly (2) NLST command.
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Analysis
by VulDB Data Team • 08/11/2024
The vulnerability identified as CVE-2006-6558 affects Crob FTP Server version 3.6.1 build 263, presenting a significant denial of service risk that can be exploited by remote attackers through carefully crafted FTP commands. This flaw specifically targets the server's handling of LIST and NLST commands, which are fundamental operations in the File Transfer Protocol for directory listing and file name retrieval. The attack vector involves sending a series of "?A" sequences that, when processed by the vulnerable server, trigger an abnormal termination of the service, effectively rendering the FTP server unavailable to legitimate users.
The technical implementation of this vulnerability stems from insufficient input validation and buffer handling within the FTP server's command processing routines. When the server receives the LIST or NLST commands containing extended sequences of "?A" characters, the internal parsing mechanism fails to properly handle the excessive input length, leading to a resource exhaustion condition or stack overflow scenario. This type of vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers stack-based buffer overflow conditions. The flaw represents a classic example of inadequate bounds checking in network protocol implementations where attackers can manipulate input parameters to cause system instability.
The operational impact of this vulnerability extends beyond simple service disruption as it can be exploited by malicious actors to perform sustained denial of service attacks against FTP services. Remote attackers need no authentication credentials to exploit this vulnerability, making it particularly dangerous in environments where FTP servers are exposed to untrusted networks. The attack can be executed through standard FTP client tools or automated scripts, allowing for rapid deployment and potential amplification of impact. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under the T1499 category for network denial of service, where adversaries leverage weaknesses in network services to interrupt availability of systems and applications.
Organizations running Crob FTP Server 3.6.1 build 263 should immediately implement mitigations including applying the latest security patches from the vendor, implementing network-level restrictions such as firewall rules that limit the length of FTP command parameters, and monitoring for suspicious FTP traffic patterns. Network segmentation strategies should be employed to isolate FTP services from critical infrastructure, and intrusion detection systems should be configured to alert on unusual command sequences. Additionally, administrators should consider implementing rate limiting on FTP command processing and establishing automated monitoring for service availability to detect potential exploitation attempts. The vulnerability demonstrates the critical importance of input validation in network services and highlights how seemingly benign command parameters can be weaponized to compromise system availability and service integrity.