CVE-2009-4593 in bftpd
Summary
by MITRE
The bftpdutmp_log function in bftpdutmp.c in Bftpd before 2.4 does not place a \0 character at the end of the string value of the ut.bu_host structure member, which might allow remote attackers to cause a denial of service (daemon crash) via unspecified vectors. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 01/26/2019
The vulnerability identified as CVE-2009-4593 affects the Bftpd FTP server software version 2.3 and earlier, specifically within the bftpdutmp.c source file where the bftpdutmp_log function handles user login tracking. This issue represents a classic buffer management flaw that can lead to daemon instability and potential denial of service conditions. The vulnerability stems from improper string termination practices within the ut.bu_host structure member, which is part of the standard utmp structure used for tracking user sessions in Unix-like operating systems. When the bftpdutmp_log function processes user login information, it fails to properly null-terminate the hostname string stored in the ut.bu_host field, creating a condition where subsequent string operations may encounter unexpected behavior.
The technical flaw manifests when Bftpd attempts to log user session information into the utmp structure, which is a fundamental system component used for tracking active user sessions and system activities. The absence of proper null termination in the ut.bu_host member creates a scenario where string processing functions may read beyond the intended buffer boundaries, potentially accessing uninitialized memory or corrupting adjacent data structures. This memory corruption can occur during various operations including string concatenation, comparison, or display functions that expect null-terminated strings. The vulnerability is particularly dangerous because it can be triggered remotely through FTP login attempts, making it an attractive target for attackers seeking to disrupt FTP services without requiring local system access or authentication.
From an operational impact perspective, this vulnerability creates a significant risk for systems running vulnerable versions of Bftpd, as remote attackers can exploit the flaw to cause daemon crashes and subsequent denial of service conditions. The attack vector is relatively straightforward since it requires only the ability to establish FTP connections to the affected server, making it accessible to a broad range of potential threat actors. The instability introduced by this vulnerability can result in complete service disruption, forcing administrators to restart the FTP daemon manually and potentially disrupting legitimate user access to file transfer services. Additionally, repeated exploitation attempts could lead to persistent service degradation or even system instability in extreme cases.
The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and represents a form of improper string termination that can lead to memory corruption issues. It also maps to ATT&CK technique T1499.004, which covers network denial of service attacks through exploitation of software vulnerabilities. The attack surface is primarily limited to systems running vulnerable versions of Bftpd, but given the widespread use of FTP servers in enterprise environments, the potential impact extends across numerous organizations. Organizations should consider this vulnerability as part of their broader security posture assessment, particularly in environments where FTP services are exposed to untrusted networks. The fix for this vulnerability involves ensuring proper null termination of string values within the ut.bu_host structure member, which should be implemented through careful review and modification of the bftpdutmp.c source code to maintain compatibility with the standard utmp system structure while preventing the memory corruption conditions that lead to daemon crashes.