CVE-2008-7264 in pyftpdlib
Summary
by MITRE
The ftp_QUIT function in ftpserver.py in pyftpdlib before 0.5.0 allows remote authenticated users to cause a denial of service (file descriptor exhaustion and daemon outage) by sending a QUIT command during a disallowed data-transfer attempt.
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Analysis
by VulDB Data Team • 02/07/2019
The vulnerability described in CVE-2008-7264 represents a significant denial of service weakness within the pyftpdlib ftp server implementation that affects versions prior to 0.5.0. This issue specifically targets the ftp_QUIT function in the ftpserver.py module, creating a scenario where authenticated remote attackers can systematically exhaust file descriptors and ultimately cause daemon outages. The flaw manifests when users send QUIT commands during data transfer attempts that are not permitted by the server's current operational state, leading to resource depletion and service disruption.
The technical root cause of this vulnerability stems from inadequate state management and resource cleanup within the FTP server's command processing logic. When a QUIT command is received during a disallowed data transfer attempt, the server fails to properly release file descriptors and system resources that were allocated for the interrupted transfer operation. This resource leak occurs because the ftp_QUIT function does not properly validate the current transfer state before attempting to terminate the connection, allowing file descriptors to remain open indefinitely. The vulnerability aligns with CWE-404, which addresses improper resource cleanup, and demonstrates poor handling of concurrent operations in network services.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire FTP daemon's stability and availability. As attackers repeatedly exploit this weakness, they can systematically consume all available file descriptors, causing the server to become unresponsive to legitimate connection requests and effectively rendering the service unavailable to authorized users. This type of resource exhaustion attack can be particularly damaging in production environments where FTP services are critical for file transfer operations. The vulnerability also maps to ATT&CK technique T1499.004, which covers network denial of service attacks targeting service availability.
Mitigation strategies for this vulnerability require immediate patching of affected pyftpdlib installations to version 0.5.0 or later, where the resource management issues have been addressed through proper state validation and cleanup procedures. Additionally, system administrators should implement connection rate limiting and monitoring to detect unusual patterns of QUIT command usage that may indicate exploitation attempts. The fix involves enhancing the ftp_QUIT function to properly validate transfer states before attempting resource cleanup and ensuring that all file descriptors are properly closed regardless of the command execution context. Network-level protections such as firewall rules and intrusion detection systems can provide additional layers of defense against exploitation attempts. Organizations should also consider implementing automated monitoring for file descriptor usage patterns to proactively identify potential resource exhaustion scenarios before they result in complete service outages.