CVE-2023-3825 in KEPServerEX
Summary
by MITRE • 08/01/2023
PTC’s KEPServerEX Versions 6.0 to 6.14.263 are vulnerable to being made to read a recursively defined object that leads to uncontrolled resource consumption. KEPServerEX uses OPC UA, a protocol which defines various object types that can be nested to create complex arrays. It does not implement a check to see if such an object is recursively defined, so an attack could send a maliciously created message that the decoder would try to decode until the stack overflowed and the device crashed.
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Analysis
by VulDB Data Team • 08/20/2023
PTC KEPServerEX versions 6.0 through 6.14.263 contain a critical vulnerability that stems from inadequate validation of recursively defined objects within the OPC UA protocol implementation. This vulnerability manifests as an uncontrolled resource consumption issue that can lead to system crashes and denial of service conditions. The flaw exists in the object decoding mechanism that fails to implement proper recursion detection when processing nested OPC UA objects, creating a path for malicious actors to exploit through carefully crafted protocol messages. The vulnerability is particularly concerning because OPC UA is widely deployed in industrial control systems and manufacturing environments where continuous operation is critical for operational continuity.
The technical implementation of this vulnerability involves the absence of recursion depth checking within the OPC UA object parser used by KEPServerEX. When a maliciously constructed message containing recursively defined objects is received, the server's decoder attempts to process these nested structures without bounds checking. This leads to a stack overflow condition as the decoder continues to traverse the recursive object structure indefinitely. The vulnerability maps directly to CWE-674, which describes "Uncontrolled Recursion" in software systems, and represents a classic example of insufficient input validation in protocol handlers. The stack overflow occurs because the decoder lacks a mechanism to detect when an object references itself or creates circular dependencies that would result in infinite recursion during processing.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromising the integrity of industrial control systems that rely on KEPServerEX for OPC UA communications. Attackers could exploit this weakness to repeatedly crash the server, disrupting critical manufacturing processes and potentially causing production downtime with significant financial consequences. The vulnerability is particularly dangerous in environments where KEPServerEX serves as a gateway between different industrial systems, as a successful attack could propagate through the industrial network and affect multiple connected devices. According to ATT&CK framework, this vulnerability aligns with T1499.004 which covers "Endpoint Denial of Service" and represents a pathway for attackers to establish persistent access through system disruption.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected KEPServerEX versions to the latest releases that include recursion detection mechanisms. Organizations should also implement network segmentation to limit access to KEPServerEX systems and deploy intrusion detection systems that can identify anomalous OPC UA traffic patterns. Additional protective measures include configuring access controls to restrict which systems can communicate with KEPServerEX and implementing monitoring solutions that can detect unusual resource consumption patterns. The vulnerability highlights the importance of robust input validation in protocol implementations and serves as a reminder that industrial control systems require special attention to prevent recursive processing attacks that can compromise operational continuity. Security teams should also conduct thorough assessments of their OPC UA implementations to identify similar recursion vulnerabilities in other industrial protocols and ensure proper bounds checking is implemented across all object parsing mechanisms.