CVE-2002-0221 in EServ
Summary
by MITRE
Etype Eserv 2.97 allows remote attackers to cause a denial of service (resource exhaustion) via a large number of PASV commands that consume ports 1024 through 5000, which prevents the server from accepting valid PASV.
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Analysis
by VulDB Data Team • 09/21/2025
The vulnerability identified as CVE-2002-0221 affects the Etype Eserv 2.97 FTP server implementation and represents a classic resource exhaustion attack vector that demonstrates poor input validation and connection handling mechanisms. This vulnerability specifically targets the Passive FTP mode implementation where the server must allocate and manage port resources for data connections, creating a scenario where malicious actors can systematically deplete available port resources within the specified range of 1024 through 5000. The flaw stems from inadequate resource management where the server fails to properly track or limit the number of concurrent PASV command requests, allowing an attacker to continuously submit these commands without proper rate limiting or resource cleanup mechanisms.
The technical exploitation of this vulnerability operates through a straightforward yet effective methodology where an attacker establishes multiple FTP connections and repeatedly issues PASV commands without properly closing or disposing of the associated resources. Each PASV command requires the server to allocate a port from the specified range, and when these commands are issued in rapid succession, they consume available ports until the entire range becomes exhausted. This port exhaustion prevents legitimate users from establishing valid PASV connections, as the server cannot allocate new ports for legitimate data transfers, effectively rendering the FTP service unavailable to legitimate users while maintaining the ability to accept new connections for the control channel.
The operational impact of this vulnerability extends beyond simple service disruption to represent a fundamental flaw in the server's resource management architecture that aligns with CWE-400 weakness category related to unspecified resource exhaustion. This vulnerability can be categorized under ATT&CK technique T1499.004 for network denial of service, demonstrating how attackers can leverage protocol implementation weaknesses to achieve persistent service disruption. The vulnerability affects the availability aspect of the CIA triad and can be particularly damaging in environments where FTP services are critical for business operations, as it prevents legitimate file transfers while maintaining the server's ability to accept new control connections, creating a subtle but effective denial of service condition.
Mitigation strategies for this vulnerability should focus on implementing proper rate limiting and resource tracking mechanisms within the FTP server implementation. The most effective approaches include configuring maximum connection limits, implementing proper timeout mechanisms for PASV command processing, and ensuring that allocated ports are properly released when connections are terminated. Additionally, network-level mitigations such as implementing connection rate limiting at the firewall level can provide additional protection against this type of attack. System administrators should also consider implementing monitoring solutions that can detect unusual patterns of PASV command issuance and alert on potential resource exhaustion conditions. The vulnerability highlights the importance of proper resource management and input validation in server implementations, emphasizing that even seemingly benign protocol features can become attack vectors when proper resource handling mechanisms are not implemented.