CVE-2020-9273 in ProFTPD
Summary
by MITRE
In ProFTPD 1.3.7, it is possible to corrupt the memory pool by interrupting the data transfer channel. This triggers a use-after-free in alloc_pool in pool.c, and possible remote code execution.
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Analysis
by VulDB Data Team • 04/02/2024
The vulnerability identified as CVE-2020-9273 represents a critical memory corruption flaw in ProFTPD version 1.3.7 that stems from improper handling of data transfer interruptions. This issue manifests when the FTP server encounters unexpected termination of data channel connections during active file transfers, creating a scenario where memory management structures become compromised. The root cause lies within the alloc_pool function located in pool.c, which fails to properly validate or handle the state of memory pools when interrupt signals are received during data transfer operations. This fundamental flaw in resource management creates a use-after-free condition that can be exploited by remote attackers to execute arbitrary code on the affected system.
The technical implementation of this vulnerability involves a specific sequence of events that begins with establishing a data channel connection for file transfers and continues through the interruption of that channel during active data movement. When the data transfer is abruptly terminated, the memory pool management system in ProFTPD does not correctly handle the cleanup or validation of allocated memory blocks, leading to situations where freed memory regions are accessed or reused improperly. This use-after-free condition occurs because the alloc_pool function lacks proper synchronization mechanisms and state validation checks that would normally prevent access to memory that has already been deallocated. The flaw operates at the core memory management layer of the FTP server, making it particularly dangerous as it can be triggered through normal network operations without requiring special privileges or authentication.
The operational impact of CVE-2020-9273 extends beyond simple memory corruption, presenting a significant threat to system security and availability. Remote attackers can leverage this vulnerability to achieve arbitrary code execution on systems running vulnerable ProFTPD versions, potentially allowing them to gain full control over the affected server. The attack surface is broad since FTP servers are commonly accessible over the internet and often contain sensitive data or serve as entry points for larger network breaches. Once exploited, this vulnerability could enable attackers to establish persistent access, escalate privileges, or use the compromised system as a launching point for further attacks against internal networks. The remote nature of the exploit means that attackers do not need physical access to the system or local network presence, making it particularly concerning for organizations with publicly accessible FTP services.
Mitigation strategies for CVE-2020-9273 require immediate action to address the underlying memory management flaw in ProFTPD. Organizations should prioritize upgrading to ProFTPD version 1.3.8 or later, which contains patches specifically designed to address the memory pool corruption issue and prevent use-after-free conditions during data transfer interruptions. System administrators should also implement network-level protections such as firewalls and intrusion detection systems to monitor for suspicious FTP traffic patterns that might indicate exploitation attempts. Additionally, disabling unnecessary FTP services and implementing strong access controls can reduce the attack surface, while regular security audits and vulnerability assessments should be conducted to identify similar issues in other network services. The vulnerability aligns with CWE-416, which specifically addresses use-after-free errors, and represents a clear violation of secure coding practices that should be addressed through proper memory management validation and error handling mechanisms. Organizations should also consider implementing runtime protections and monitoring solutions that can detect anomalous memory access patterns indicative of exploitation attempts.