CVE-2019-5185 in PFC 200
Summary
by MITRE
An exploitable stack buffer overflow vulnerability vulnerability exists in the iocheckd service "I/O-Check" functionality of WAGO PFC 200. An attacker can send a specially crafted packet to trigger the parsing of this cache file. At 0x1ea28 the extracted state value from the xml file is used as an argument to /etc/config-tools/config_interfaces interface=X1 state=<contents of state node> using sprintf(). The destination buffer sp+0x40 is overflowed with the call to sprintf() for any state values that are greater than 512-len("/etc/config-tools/config_interfaces interface=X1 state=") in length. Later, at 0x1ea08 strcpy() is used to copy the contents of the stack buffer that was overflowed sp+0x40 into sp+0x440. The buffer sp+0x440 is immediately adjacent to sp+0x40 on the stack. Therefore, there is no NULL termination on the buffer sp+0x40 since it overflowed into sp+0x440. The strcpy() will result in invalid memory access. An state value of length 0x3c9 will cause the service to crash.
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Analysis
by VulDB Data Team • 04/30/2024
The vulnerability described in CVE-2019-5185 represents a critical stack buffer overflow within the iocheckd service of WAGO PFC 200 industrial control devices. This flaw resides in the I/O-Check functionality that processes configuration files through XML parsing mechanisms, creating a pathway for remote exploitation. The vulnerability stems from improper input validation and unsafe string handling practices within the service's code execution flow, specifically affecting industrial IoT systems that require robust security measures due to their critical infrastructure roles.
The technical implementation of this vulnerability occurs at the memory manipulation level where the system processes XML configuration data containing state values. During the parsing operation at address 0x1ea28, the extracted state value from the XML file is directly incorporated into a command string using sprintf() function without adequate length validation. The destination buffer located at sp+0x40 has a fixed size limitation that cannot accommodate state values exceeding 512 characters minus the length of the command prefix "/etc/config-tools/config_interfaces interface=X1 state=". When this threshold is exceeded, the sprintf() operation causes a stack buffer overflow that overflows into adjacent memory locations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable arbitrary code execution within the industrial control environment. The subsequent use of strcpy() at address 0x1ea08 to copy the overflowed stack contents from sp+0x40 into sp+0x440 creates a chained memory corruption scenario where the lack of proper null termination in the overflowed buffer leads to invalid memory access patterns. This memory corruption can result in service crashes, system instability, or potentially more severe consequences in industrial control systems where reliability is paramount. The specific trigger condition requires a state value of exactly 0x3c9 (969) characters to reliably cause the service to crash, demonstrating the precise nature of the buffer boundary violation.
This vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which classifies the flaw as a direct result of insufficient bounds checking during string operations. The attack vector follows patterns consistent with ATT&CK technique T1203 Exploitation for Client Execution, where an attacker can craft malicious input to exploit the buffer overflow. The industrial control system context makes this particularly concerning as it affects WAGO PFC 200 devices commonly deployed in critical infrastructure environments where such vulnerabilities could lead to operational disruptions, safety hazards, or security breaches. The vulnerability represents a significant risk to industrial IoT security, emphasizing the need for proper input validation and secure coding practices in embedded systems. Organizations should implement immediate mitigation measures including network segmentation, service hardening, and firmware updates to address this vulnerability before it can be exploited in operational environments.