CVE-2007-6263 in ftp
Summary
by MITRE
The dataconn function in ftpd.c in netkit ftpd (netkit-ftpd) 0.17, when certain modifications to support SSL have been introduced, calls fclose on an uninitialized file stream, which allows remote attackers to cause a denial of service (daemon crash) and possibly have unspecified other impact via some types of FTP over SSL protocol behavior, as demonstrated by breaking a passive FTP DATA connection in a way that triggers an error in the server s SSL_accept function. NOTE: the netkit ftp issue is covered by CVE-2007-5769.
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Analysis
by VulDB Data Team • 08/05/2019
The vulnerability described in CVE-2007-6263 affects the netkit-ftpd implementation of the File Transfer Protocol daemon, specifically targeting the dataconn function within ftpd.c. This flaw emerges from modifications made to support SSL functionality, creating a critical programming error that manifests when handling FTP over SSL connections. The vulnerability is particularly concerning because it represents a classic case of improper resource management where a file stream remains uninitialized while still being subject to fclose operations, creating a fundamental memory management issue that can be exploited by remote attackers.
The technical implementation of this vulnerability stems from the improper handling of file streams during SSL connection establishment and data transfer phases. When the SSL_accept function fails during passive FTP data connection establishment, the dataconn function attempts to close a file stream that was never properly initialized or allocated. This uninitialized stream reference leads to undefined behavior in the daemon process, causing immediate termination and resulting in a denial of service condition. The vulnerability is particularly insidious because it occurs during legitimate SSL protocol operations, making it difficult to distinguish between normal protocol behavior and malicious exploitation attempts. The flaw demonstrates poor coding practices that align with CWE-459, which describes incomplete cleanup issues in resource management, and CWE-476, addressing null pointer dereference conditions that can occur when uninitialized pointers are dereferenced.
The operational impact of this vulnerability extends beyond simple service disruption, as it can potentially allow attackers to execute arbitrary code or cause additional system instability through the daemon crash. Remote attackers can trigger this condition by initiating specific FTP over SSL protocol sequences that force the server to enter error states during SSL negotiation. The vulnerability affects systems running netkit-ftpd version 0.17 and potentially other versions that incorporate similar SSL modification patterns. The attack vector requires network access to the FTP daemon and knowledge of SSL FTP protocols, making it moderately accessible to skilled attackers while still requiring some understanding of the underlying protocol implementation. This vulnerability represents a significant risk to organizations relying on FTP services, particularly those implementing SSL/TLS encryption for secure data transfer.
Mitigation strategies for this vulnerability include immediate patching of the netkit-ftpd implementation to address the uninitialized file stream handling in the dataconn function, which aligns with ATT&CK technique T1190 for exploiting vulnerabilities in network services. System administrators should also implement network segmentation and access controls to limit exposure of FTP services to untrusted networks. Additionally, monitoring for unusual FTP protocol behavior and connection patterns can help detect exploitation attempts. Organizations should consider migrating to more modern FTP implementations or secure alternatives such as SFTP or FTPS with proper error handling, as this vulnerability demonstrates the risks associated with legacy protocol implementations that have not been adequately updated for security considerations. The fix typically involves ensuring proper initialization of file streams before any close operations are attempted, which directly addresses the root cause of the resource management failure.