CVE-2003-0466 in Libc
Summary
by MITRE
Off-by-one error in the fb_realpath() function, as derived from the realpath function in BSD, may allow attackers to execute arbitrary code, as demonstrated in wu-ftpd 2.5.0 through 2.6.2 via commands that cause pathnames of length MAXPATHLEN+1 to trigger a buffer overflow, including (1) STOR, (2) RETR, (3) APPE, (4) DELE, (5) MKD, (6) RMD, (7) STOU, or (8) RNTO.
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Analysis
by VulDB Data Team • 08/13/2025
The vulnerability identified as CVE-2003-0466 represents a critical buffer overflow flaw originating from an off-by-one error within the fb_realpath() function implementation in wu-ftpd versions 2.5.0 through 2.6.2. This function, which is derived from the standard BSD realpath function, serves as a crucial component for resolving symbolic links and normalizing file paths within the FTP server's operation. The flaw manifests when processing file pathnames that exceed the maximum allowed length of MAXPATHLEN+1 characters, creating a condition where memory boundaries are violated and attacker-controlled data can overwrite adjacent memory regions. The vulnerability specifically affects eight core FTP commands that manipulate file paths including STOR for storing files, RETR for retrieving files, APPE for appending data, DELE for deleting files, MKD for creating directories, RMD for removing directories, STOU for storing unique files, and RNTO for renaming files. This represents a classic buffer overflow scenario where the error occurs during path resolution rather than during direct data handling, making it particularly insidious as it can be triggered through legitimate FTP operations that users might perform routinely.
The technical implementation of this vulnerability stems from improper boundary checking in the fb_realpath() function's memory allocation and string handling logic. When the function processes a pathname exceeding MAXPATHLEN characters, the off-by-one error causes the function to allocate insufficient memory for the resolved path, leading to a situation where one additional character of input data overflows into adjacent memory locations. This memory corruption can potentially overwrite return addresses, function pointers, or other critical control data structures within the program's memory space. The attack vector is particularly dangerous because it leverages legitimate FTP commands that administrators and users would routinely execute without suspecting malicious activity. The vulnerability's exploitation requires precise control over the input data length to trigger the exact memory layout that allows code execution, making it a sophisticated target for attackers who can craft payloads that overwrite critical execution flow information. The flaw essentially creates a race condition between normal program execution and attacker-controlled memory corruption, where the buffer overflow occurs during the path normalization process rather than during data transfer operations.
The operational impact of this vulnerability extends far beyond simple denial of service scenarios, as it can enable complete system compromise through arbitrary code execution. When successfully exploited, attackers can gain control over the FTP server process and potentially escalate privileges to the level of the running service, which typically operates with elevated system permissions. This makes the vulnerability particularly attractive to attackers seeking persistent access to systems, as the compromised FTP server can serve as a foothold for broader network infiltration. The vulnerability affects a wide range of Unix-based systems that rely on wu-ftpd for file transfer operations, including web servers, file servers, and network infrastructure components that use this FTP implementation. The attack surface is significant because FTP commands are commonly used in automated processes, backup operations, and system administration tasks, making it difficult to predict when or how an attacker might exploit this vulnerability. Additionally, the vulnerability's exploitation is not limited to direct network access, as attackers can potentially leverage it through compromised accounts or systems that have legitimate FTP access, making it a persistent threat to organizations with multiple FTP server deployments.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security improvements within the affected systems. The primary recommendation involves upgrading to patched versions of wu-ftpd that contain proper boundary checking and memory allocation corrections for the fb_realpath() function, specifically versions beyond 2.6.2 where the vulnerability has been addressed. Organizations should also implement network-level controls such as firewall rules that restrict FTP access to trusted networks and limit the exposure of FTP services to external internet traffic. Additional defensive measures include implementing strict input validation for all FTP commands that handle file paths, monitoring for unusual path length patterns that might indicate exploitation attempts, and deploying intrusion detection systems that can identify the specific command sequences associated with this vulnerability. The fix for this issue aligns with common software security practices outlined in the CWE (Common Weakness Enumeration) catalog under CWE-121, which addresses stack-based buffer overflow conditions, and follows ATT&CK framework techniques such as T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. Organizations should also consider implementing principle of least privilege for FTP service accounts and regularly audit FTP server configurations to prevent unauthorized access to sensitive file operations that could facilitate exploitation of this vulnerability.