CVE-2003-1329 in wu-ftpd
Summary
by MITRE
ftpd.c in wu-ftpd 2.6.2, when running on "operating systems that only allow one non-connected socket bound to the same local address," does not close failed connections, which allows remote attackers to cause a denial of service.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability identified as CVE-2003-1329 resides within the wu-ftpd 2.6.2 implementation of the ftpd.c file, specifically targeting systems where the operating environment restricts multiple non-connected sockets to share the same local address binding. This constraint creates a unique scenario where the FTP daemon fails to properly manage socket resources during connection attempts, leading to a resource exhaustion condition that can be exploited by remote attackers. The flaw manifests when the FTP server encounters failed connection attempts and fails to close the associated socket descriptors, resulting in a gradual accumulation of open file descriptors that eventually exhausts the system's available socket resources.
The technical root cause of this vulnerability stems from improper resource management within the FTP daemon's connection handling logic. When the wu-ftpd server processes incoming connection requests on systems with restrictive socket binding policies, it encounters situations where connection establishment fails due to the operating system's limitation on binding multiple sockets to identical local addresses. Under normal circumstances, the server should close these failed connection sockets to free up system resources, but the implementation defect prevents this cleanup process from occurring properly. This resource leak becomes particularly problematic when attackers repeatedly attempt connections that fail due to the system's socket binding restrictions, creating a cumulative effect that gradually consumes available file descriptors and network resources.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader system stability concerns. Remote attackers can exploit this weakness by initiating multiple connection attempts that consistently fail due to the underlying socket binding limitations, causing the FTP daemon to maintain an increasing number of open socket connections that never get properly closed. As the number of leaked file descriptors grows, the system eventually reaches its maximum file descriptor limit, preventing the FTP daemon from accepting new legitimate connection requests and effectively rendering the service unavailable to legitimate users. This denial of service condition can persist until the system is manually restarted or the resource exhaustion is manually addressed through process management.
This vulnerability aligns with CWE-404, which addresses improper resource management, specifically focusing on the failure to release resources properly during error conditions. The flaw also demonstrates characteristics consistent with ATT&CK technique T1499.004, which involves resource exhaustion attacks targeting network services through denial of service mechanisms. The exploitation pattern involves sustained connection attempts that leverage the operating system's inherent socket binding limitations to create a persistent resource leak. Security practitioners should note that this vulnerability represents a classic example of how operating system constraints can interact with application-level resource management to create unexpected security implications. The remediation approach typically involves patching the wu-ftpd implementation to ensure proper socket closure during failed connection attempts, or upgrading to more modern FTP server implementations that handle resource management more robustly.
The broader implications of this vulnerability highlight the importance of understanding how system-level constraints can interact with application behavior to create security weaknesses. Organizations running wu-ftpd 2.6.2 on affected systems should prioritize immediate patching or migration to more secure FTP implementations, as the vulnerability can be exploited with minimal technical expertise. The resource management failure described in this vulnerability serves as a reminder of the critical importance of proper error handling and resource cleanup in network service implementations, particularly in environments where operating system limitations may exacerbate application-level design flaws.