CVE-2004-0656 in PureFTPd
Summary
by MITRE
The accept_client function in PureFTPd 1.0.18 and earlier allows remote attackers to cause a denial of service by exceeding the maximum number of connections.
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Analysis
by VulDB Data Team • 06/30/2021
The vulnerability identified as CVE-2004-0656 affects PureFTPd versions 1.0.18 and earlier, specifically within the accept_client function implementation. This flaw represents a classic denial of service vulnerability that exploits the server's connection handling mechanism. The issue occurs when remote attackers systematically exceed the maximum number of allowed connections, causing the FTP server to become unresponsive and unable to accept new client connections. The vulnerability stems from inadequate connection management and lack of proper rate limiting or connection throttling mechanisms within the server's core networking code.
From a technical perspective, the accept_client function in PureFTPd fails to properly validate or limit incoming connection attempts beyond the configured maximum threshold. When this threshold is exceeded, the server enters a state where it cannot properly process new connection requests or maintain existing connections, effectively rendering the service unavailable to legitimate users. The flaw operates at the protocol level where the server's network stack does not adequately handle connection overflow conditions, leading to resource exhaustion or internal state corruption that prevents normal operation. This vulnerability aligns with CWE-400 which categorizes improper handling of resource exhaustion conditions and represents a fundamental flaw in the server's connection management architecture.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect business continuity and availability of file transfer services. Organizations relying on PureFTPd for data exchange operations could experience complete service outages when subjected to this attack, particularly in environments where FTP services are critical for business operations. The vulnerability can be exploited by any remote attacker with network access to the FTP server, making it particularly dangerous in publicly accessible environments. Attackers can leverage this flaw to perform simple but effective denial of service attacks that do not require sophisticated techniques or privileged access, making the vulnerability highly exploitable across various network configurations.
Mitigation strategies for CVE-2004-0656 should focus on immediate software updates to versions that address the connection handling flaw. Organizations should implement connection rate limiting and monitoring to detect abnormal connection patterns that may indicate exploitation attempts. Network-level protections including firewall rules and connection tracking mechanisms can help limit the impact of such attacks by restricting the number of concurrent connections from individual IP addresses. Additionally, implementing proper logging and alerting systems around connection limits can provide early detection of potential exploitation attempts. The vulnerability demonstrates the importance of proper resource management in server applications and aligns with ATT&CK technique T1499 which covers resource exhaustion attacks targeting availability. Organizations should also consider implementing redundant FTP services or alternative file transfer protocols to maintain operational continuity during potential attack scenarios.