CVE-2008-7263 in pyftpdlib
Summary
by MITRE
ftpserver.py in pyftpdlib before 0.5.0 does not delay its response after receiving an invalid login attempt, which makes it easier for remote attackers to obtain access via a brute-force attack.
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Analysis
by VulDB Data Team • 02/07/2019
The vulnerability identified as CVE-2008-7263 affects the pyftpdlib ftpserver.py component in versions prior to 0.5.0, creating a significant security weakness that directly impacts authentication security mechanisms. This flaw resides in the server's response handling during failed authentication attempts, where the system fails to implement proper timing delays or rate limiting measures. The vulnerability specifically targets the FTP protocol implementation within the Python-based pyftpdlib library, which is commonly used for creating FTP servers in various network environments. The absence of response delays creates a timing side-channel attack vector that significantly weakens the system's resistance to automated brute-force attacks. This issue represents a critical flaw in the library's security design as it directly enables attackers to systematically test multiple credential combinations without encountering the normal delays that would typically slow down such automated attempts. The vulnerability falls under the category of timing attacks and weak authentication mechanisms, which are classified under CWE-307 and CWE-308 in the Common Weakness Enumeration catalog.
The technical implementation flaw occurs at the authentication response level where the ftpserver.py component immediately processes and responds to failed login attempts without introducing any form of artificial delay or rate limiting. This behavior creates a predictable timing pattern that attackers can exploit to distinguish between valid and invalid login attempts through timing analysis. The lack of response delay means that valid login attempts and invalid login attempts return responses with minimal time differences, making it extremely easy for automated tools to perform rapid brute-force attacks. This timing inconsistency provides attackers with clear feedback mechanisms that enable them to quickly identify successful authentication attempts. The vulnerability directly violates security best practices for authentication systems as outlined in the NIST SP 800-63 standard, which emphasizes the importance of implementing proper rate limiting and timing controls to prevent automated attack vectors. Attackers can leverage this weakness to systematically iterate through username and password combinations, significantly reducing the time required to compromise accounts compared to systems that properly implement response delays.
The operational impact of this vulnerability extends beyond simple credential compromise, as it fundamentally undermines the security posture of any system utilizing the affected pyftpdlib version. Organizations deploying FTP servers through this library become vulnerable to rapid credential guessing attacks that can result in unauthorized access to sensitive data and system resources. The vulnerability is particularly dangerous in environments where FTP services are exposed to the internet or where weak password policies are in place, as it eliminates the primary defense mechanism of rate limiting that would normally slow down automated attacks. The timing-based attack vector allows for efficient exploitation even with relatively simple attack tools, making this vulnerability particularly attractive to threat actors. This flaw can be easily automated and scaled, potentially leading to complete system compromise and data breaches. The vulnerability also creates a persistent risk that remains active until the library is updated, as the issue exists in the core authentication handling logic rather than being a configuration problem. The impact is further amplified because FTP servers often handle sensitive data and may be part of larger enterprise infrastructure where unauthorized access could lead to significant business disruption and regulatory compliance violations.
Mitigation strategies for CVE-2008-7263 primarily focus on updating to pyftpdlib version 0.5.0 or later, which includes proper response delay mechanisms for failed authentication attempts. Organizations should also implement additional security controls such as IP address filtering, connection rate limiting, and intrusion detection systems to reduce the effectiveness of brute-force attacks. Network-level protections including firewall rules that limit FTP access to trusted IP ranges and implementing authentication mechanisms such as SSH key-based authentication can provide additional layers of defense. The implementation of account lockout policies and the enforcement of strong password requirements can further reduce the risk associated with this vulnerability. Security administrators should also consider monitoring FTP server logs for unusual login patterns and implementing automated alerting systems to detect potential brute-force attack attempts. The vulnerability serves as a reminder of the importance of implementing proper timing controls in authentication systems and aligns with ATT&CK technique T1110.003 for Brute Force Attacks, emphasizing the need for defensive measures that prevent rapid credential testing. Organizations should also regularly update their software dependencies and maintain inventory of all components using pyftpdlib to ensure timely patching of similar vulnerabilities. The remediation process requires not only updating the library but also reviewing and strengthening overall FTP security policies to prevent exploitation of similar timing-based weaknesses in other authentication systems.