CVE-2020-8416 in BearFTP
Summary
by MITRE
BearFTP before 0.2.0 allows remote attackers to achieve denial of service via a large volume of connections to the PASV mode port.
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Analysis
by VulDB Data Team • 08/17/2024
The vulnerability identified as CVE-2020-8416 affects BearFTP versions prior to 0.2.0 and represents a denial of service condition that can be exploited by remote attackers through excessive connection attempts to the PASV mode port. This issue falls under the category of resource exhaustion attacks where malicious actors can overwhelm the FTP server's ability to handle legitimate connections by flooding the system with numerous simultaneous connection requests. The PASV mode in FTP protocols is designed to allow the server to specify a port number for data connections, but in this case the implementation fails to properly manage or limit incoming connection attempts, creating a pathway for attackers to exhaust available system resources.
The technical flaw manifests in the insufficient connection handling mechanisms within BearFTP's PASV mode implementation. When multiple clients attempt to establish connections to the PASV port simultaneously, the application fails to implement proper rate limiting or connection queuing mechanisms that would normally prevent such resource exhaustion scenarios. This vulnerability directly maps to CWE-400 which describes unchecked resource consumption, and specifically relates to the broader category of denial of service attacks where system resources become unavailable to legitimate users. The flaw exists because the software does not adequately validate or limit the number of concurrent connection attempts that can be made to the PASV mode port, allowing an attacker to simply open many connections in quick succession to deplete available file descriptors or connection slots.
From an operational impact perspective, this vulnerability enables remote attackers to effectively disrupt service availability for legitimate users by consuming all available connection resources. The attack can be executed without requiring authentication or special privileges, making it particularly dangerous as it can be launched from any network location. Organizations relying on BearFTP for file transfer services may experience complete service disruption when this vulnerability is exploited, leading to business continuity issues and potential loss of productivity. The impact extends beyond simple service interruption as it can affect other network services that depend on the same infrastructure, potentially causing cascading failures within larger network environments. This type of attack aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, demonstrating how attackers can leverage protocol implementation weaknesses to compromise availability.
The mitigation strategy for CVE-2020-8416 involves upgrading to BearFTP version 0.2.0 or later where the connection handling has been properly implemented to prevent resource exhaustion. System administrators should also consider implementing network-level rate limiting or firewall rules that restrict the number of connections that can be established to the PASV port within a given time period. Additional protective measures include monitoring connection patterns for unusual spikes that might indicate exploitation attempts, implementing connection timeouts for idle sessions, and ensuring proper resource limits are configured on the operating system level to prevent complete system exhaustion. Organizations should also review their FTP server configurations to ensure that connection limits are appropriately enforced and that logging mechanisms are in place to detect potential exploitation attempts. The fix addresses the root cause by implementing proper connection management and resource allocation controls that prevent malicious actors from consuming all available resources while maintaining legitimate service availability for authorized users.