CVE-2011-5166 in KnFTP
Summary
by MITRE
Multiple stack-based buffer overflows in KnFTP 1.0.0 allow remote attackers to execute arbitrary code via a long string to the (1) USER, (2) PASS, (3) REIN, (4) QUIT, (5) PORT, (6) PASV, (7) TYPE, (8) STRU, (9) MODE, (10) RETR, (11) STOR, (12) APPE, (13) ALLO, (14) REST, (15) RNFR, (16) RNTO, (17) ABOR, (18) DELE, (19) CWD, (20) LIST, (21) NLST, (22) SITE, (23) STST, (24) HELP, (25) NOOP, (26) MKD, (27) RMD, (28) PWD, (29) CDUP, (30) STOU, (31) SNMT, (32) SYST, and (33) XPWD commands.
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Analysis
by VulDB Data Team • 03/03/2025
The vulnerability described in CVE-2011-5166 represents a critical stack-based buffer overflow issue affecting KnFTP version 1.0.0, a lightweight ftp client application. This flaw exists across a comprehensive range of ftp protocol commands, making it particularly dangerous as it can be exploited through multiple attack vectors within the ftp communication protocol. The vulnerability stems from insufficient input validation and bounds checking mechanisms within the application's handling of ftp command parameters, creating opportunities for malicious actors to manipulate memory structures through crafted input strings.
The technical implementation of this vulnerability involves the exploitation of stack memory corruption through buffer overflows that occur when the application processes ftp commands containing excessively long strings. Each of the 33 identified ftp commands presents a potential entry point for attackers to inject malicious payloads that exceed the allocated buffer space, causing stack corruption that can be leveraged to overwrite return addresses and execute arbitrary code. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety issue in software development practices.
The operational impact of this vulnerability extends beyond simple denial of service conditions to enable full remote code execution capabilities for attackers. When successfully exploited, the buffer overflow allows malicious actors to gain control over the target system running KnFTP, potentially leading to complete system compromise. The wide array of affected commands means that exploitation can occur during various ftp operations, including authentication, file transfers, directory navigation, and system information retrieval. This vulnerability directly aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as attackers can leverage the compromised application to execute arbitrary commands on the target system.
The exploitation of this vulnerability requires attackers to send specially crafted long strings to any of the affected ftp commands, making it relatively straightforward to implement automated attacks against vulnerable systems. The lack of proper input sanitization and bounds checking in the application's ftp protocol implementation creates a persistent threat that remains viable as long as vulnerable versions of KnFTP are deployed. Organizations using this ftp client should immediately implement mitigations including software updates, input validation enforcement, and network segmentation to prevent unauthorized access and exploitation attempts.
Security practitioners should note that this vulnerability demonstrates the importance of robust input validation in network protocol implementations and highlights the need for comprehensive security testing of ftp client applications. The widespread impact across multiple ftp commands indicates a systemic design flaw that requires complete code review and remediation rather than isolated patching approaches. This vulnerability also underscores the critical importance of keeping ftp client software updated and following secure coding practices that prevent buffer overflow conditions through proper memory management and input validation techniques.