CVE-2010-3494 in pyftpdlib
Summary
by MITRE
Race condition in the FTPHandler class in ftpserver.py in pyftpdlib before 0.5.2 allows remote attackers to cause a denial of service (daemon outage) by establishing and then immediately closing a TCP connection, leading to the accept function having an unexpected value of None for the address, or an ECONNABORTED, EAGAIN, or EWOULDBLOCK error, a related issue to CVE-2010-3492.
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Analysis
by VulDB Data Team • 09/27/2021
The vulnerability described in CVE-2010-3494 represents a critical race condition flaw within the pyftpdlib FTP server implementation that specifically affects versions prior to 0.5.2. This issue manifests within the FTPHandler class in the ftpserver.py file where concurrent connection handling creates exploitable timing windows. The vulnerability stems from improper synchronization mechanisms during TCP connection establishment and termination processes, creating opportunities for malicious actors to disrupt normal service operations through carefully crafted connection sequences.
The technical exploitation of this race condition occurs when remote attackers establish a TCP connection to the FTP daemon and immediately terminate it without proper handshaking. This rapid connection and disconnection sequence triggers an unexpected state in the accept function where the address parameter receives a None value instead of the expected connection details. Additionally, the system encounters ECONNABORTED, EAGAIN, or EWOULDBLOCK error conditions that are not properly handled by the vulnerable code path. These error conditions arise because the FTP server's connection handling logic does not adequately account for the timing window between connection establishment and the subsequent connection closure, leading to improper state management and potential daemon crashes.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire FTP daemon availability. When exploited successfully, the race condition causes the FTP server to enter an unstable state where subsequent legitimate connections may fail or the entire service may become unresponsive. This denial of service condition affects system administrators who rely on consistent FTP service availability for file transfer operations, potentially impacting critical business processes that depend on file sharing capabilities. The vulnerability's relationship to CVE-2010-3492 indicates it represents part of a broader class of connection handling flaws that affect the pyftpdlib library's core networking functionality.
From a cybersecurity perspective, this vulnerability aligns with CWE-362, which describes race conditions in concurrent programming environments where multiple threads or processes access shared resources without proper synchronization. The ATT&CK framework categorizes this as a Denial of Service technique under the T1499 sub-technique, specifically targeting service availability through exploitation of software flaws. Organizations using pyftpdlib versions prior to 0.5.2 face significant risk exposure as this vulnerability can be exploited by anyone with network access to the FTP service, making it particularly dangerous in publicly accessible environments. The vulnerability demonstrates the importance of proper error handling and state management in network services, particularly when dealing with connection lifecycle events that occur rapidly in concurrent environments.
The recommended mitigation strategy involves upgrading to pyftpdlib version 0.5.2 or later, which contains the necessary code fixes to properly handle the race condition scenarios. System administrators should also implement connection rate limiting and monitoring mechanisms to detect unusual connection patterns that might indicate exploitation attempts. Additionally, network segmentation and access controls should be implemented to limit exposure of FTP services to only trusted networks and users, reducing the attack surface for this particular vulnerability. The fix typically involves implementing proper synchronization mechanisms and robust error handling around connection state transitions to prevent the None address values and error conditions from causing daemon instability.