CVE-2019-3940 in WebAccess
Summary
by MITRE
Advantech WebAccess 8.3.4 is vulnerable to file upload attacks via unauthenticated RPC call. An unauthenticated, remote attacker can use this vulnerability to execute arbitrary code.
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Analysis
by VulDB Data Team • 08/28/2023
The vulnerability identified as CVE-2019-3940 affects Advantech WebAccess version 8.3.4, a industrial automation and monitoring platform widely used in critical infrastructure environments. This security flaw represents a critical weakness in the platform's authentication mechanisms and input validation processes. The vulnerability specifically manifests through an unauthenticated remote procedure call interface that permits file upload operations without proper verification of the caller's identity or authorization status. This creates a significant attack vector that can be exploited by malicious actors without requiring any credentials or prior access to the system.
The technical implementation of this vulnerability stems from inadequate input sanitization and authentication controls within the RPC endpoint. When an attacker sends a specially crafted request to the vulnerable WebAccess service, the system fails to validate whether the request originates from an authorized user or system. The absence of proper authentication checks combined with insufficient file validation allows attackers to upload malicious files directly to the server's file system. This flaw falls under the CWE-434 category of Unrestricted Upload of File with Dangerous Type, which is classified as a high-risk vulnerability due to its potential for arbitrary code execution. The vulnerability exists in the RPC communication layer where file upload functionality is exposed without proper access controls, creating an attack surface that can be leveraged for privilege escalation and system compromise.
The operational impact of this vulnerability extends far beyond simple remote code execution capabilities. Industrial control systems that rely on Advantech WebAccess for monitoring and control operations face significant risks when this vulnerability is exploited. Attackers can upload malicious executables, backdoor programs, or other harmful payloads that can persist on the system and provide ongoing access to the compromised infrastructure. The remote nature of the attack means that adversaries can exploit this vulnerability from anywhere on the internet without requiring physical access to the facility or network. This vulnerability directly aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to Initial Access through Remote Services and Execution through File and Directory Permissions Modification. The compromised system can then serve as a foothold for lateral movement throughout the industrial network, potentially leading to widespread disruption of critical operations and compromise of operational technology infrastructure.
Organizations utilizing Advantech WebAccess 8.3.4 should implement immediate mitigations to address this vulnerability. The most effective immediate solution involves patching the software to the latest version that contains proper authentication controls and input validation for RPC endpoints. Network segmentation and firewall rules should be implemented to restrict access to the affected RPC services only to authorized systems and personnel. Additionally, monitoring should be enhanced to detect unusual file upload activities or unauthorized access attempts to the WebAccess service. System administrators should also consider implementing intrusion detection systems that can identify patterns associated with exploitation attempts. The vulnerability highlights the importance of securing industrial control system interfaces and demonstrates how legacy systems can contain critical flaws that persist across multiple versions without proper security updates. Organizations should establish comprehensive patch management processes and conduct regular vulnerability assessments to identify similar issues in their industrial control infrastructure, as this vulnerability represents a common pattern of insecure remote procedure call implementations in industrial automation platforms.