CVE-2003-1206 in FTP Server
Summary
by MITRE
Format string vulnerability in Crob FTP Server 2.60.1 allows remote attackers to cause a denial of service (crash) via "%s" or "%n" sequences in (1) the username during login, or other FTP commands such as (2) dir.
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Analysis
by VulDB Data Team • 05/03/2019
The vulnerability identified as CVE-2003-1206 represents a critical format string flaw in Crob FTP Server version 2.60.1 that exposes the system to remote denial of service attacks. This weakness stems from the server's improper handling of format specifiers within user input, specifically when processing login credentials and directory listing commands. The vulnerability operates by exploiting the server's failure to properly sanitize input before using it in format string functions, creating a pathway for malicious actors to inject specially crafted sequences that can trigger unexpected behavior.
The technical implementation of this vulnerability involves the exploitation of standard format string vulnerabilities where the %s and %n sequences can be used to manipulate memory operations. When these sequences are processed in the username field during login or in directory commands, they cause the application to read from or write to memory locations that are not properly allocated or validated. The %s sequence attempts to read a string from memory, while %n writes the number of characters printed to a specified memory location, both of which can result in segmentation faults or application crashes. This flaw directly maps to CWE-134 which categorizes format string vulnerabilities as weaknesses in software that use format strings without proper validation.
The operational impact of this vulnerability extends beyond simple service disruption as it allows remote attackers to execute arbitrary code or cause system instability through carefully crafted input sequences. An attacker can exploit this vulnerability without requiring authentication, making it particularly dangerous for publicly accessible FTP servers. The crash condition occurs because the server's input validation mechanism fails to properly escape or sanitize the format specifiers, leading to memory corruption and ultimately application termination. This type of vulnerability is classified under the attack technique T1489 in the MITRE ATT&CK framework, which covers denial of service through resource exhaustion or system instability.
Mitigation strategies for this vulnerability require immediate patching of the Crob FTP Server to version 2.60.2 or later, which includes proper input sanitization and format string handling. System administrators should implement input validation controls that filter out format specifiers from user inputs, particularly during authentication and command processing phases. Network segmentation and firewall rules can help reduce the attack surface by limiting access to FTP services to trusted networks only. Additionally, implementing intrusion detection systems that monitor for suspicious format string patterns in network traffic can provide early warning of exploitation attempts. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in system design, as it shows how a single flaw in input handling can lead to complete system compromise. Organizations should also consider implementing application-level firewalls or web application firewalls that can detect and block malicious format string sequences before they reach the vulnerable application components.