CVE-2018-7833 in M340
Summary
by MITRE
An Improper Check for Unusual or Exceptional Conditions vulnerability exists in the embedded web servers in all Modicon M340, Premium, Quantum PLCs and BMXNOR0200 where an unauthenticated user can send a specially crafted XML data via a POST request to cause the web server to become unavailable
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 04/21/2020
The vulnerability identified as CVE-2018-7833 represents a critical weakness in the embedded web server implementations of several Modicon PLC models including M340, Premium, Quantum series, and BMXNOR0200 devices. This flaw falls under the category of improper check for unusual or exceptional conditions as defined by CWE-254, which occurs when software fails to properly handle exceptional circumstances that should trigger error responses or system failures. The vulnerability specifically affects industrial control systems that are part of the broader industrial internet of things ecosystem, where these PLCs serve as critical components in manufacturing and process control environments.
The technical implementation of this vulnerability stems from inadequate input validation within the embedded web server functionality of these programmable logic controllers. When an unauthenticated attacker sends a specially crafted XML payload through a POST request to the affected web server, the system fails to properly validate or sanitize the incoming data structure. This lack of proper input sanitization creates a condition where malformed XML data can cause the web server process to crash or become unresponsive, effectively leading to a denial of service condition that disrupts legitimate operational activities. The vulnerability is particularly concerning because it requires no authentication credentials to exploit, making it accessible to any external attacker with network access to the device.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise industrial control system availability and reliability. In manufacturing environments where these PLCs control critical production processes, a web server denial of service attack could result in production halts, quality control issues, and significant financial losses. The attack vector is particularly dangerous because it targets the management interface of industrial devices, which often provides access to configuration settings and operational parameters that could be exploited further. According to ATT&CK framework, this vulnerability aligns with techniques involving service stoppage and denial of service attacks against industrial control systems, potentially enabling more sophisticated attacks that leverage the initial disruption.
Mitigation strategies for CVE-2018-7833 should focus on both immediate defensive measures and long-term architectural improvements. Organizations should implement network segmentation to isolate these industrial control devices from general network access, reducing the attack surface available to unauthenticated users. Network access control lists and firewall rules should be configured to restrict access to the web server ports only to authorized management systems and personnel. Additionally, vendors should be consulted for firmware updates that address the input validation weakness, as this vulnerability represents a fundamental flaw in the software implementation that requires code-level fixes. The remediation process should include comprehensive testing to ensure that the updates do not disrupt existing operational procedures, while also implementing monitoring solutions to detect anomalous XML traffic patterns that might indicate exploitation attempts.