CVE-2019-5186 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 0x1eb9c the extracted interface element name from the xml file is used as an argument to /etc/config-tools/config_interfaces interface=<contents of interface element> using sprintf(). The destination buffer sp+0x40 is overflowed with the call to sprintf() for any interface values that are greater than 512-len("/etc/config-tools/config_interfaces interface=") 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 interface value of length 0x3c4 will cause the service to crash.
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Analysis
by VulDB Data Team • 04/30/2024
The vulnerability described in CVE-2019-5186 represents a critical stack buffer overflow flaw within the iocheckd service of WAGO PFC 200 industrial control devices. This issue resides in the I/O-Check functionality that processes configuration files through XML parsing mechanisms. The vulnerability manifests when the system processes interface element names extracted from XML configuration files, creating a dangerous chain of operations that ultimately leads to arbitrary code execution or system crash. The flaw specifically occurs at memory address 0x1eb9c where the sprintf() function is called to construct a command string using data extracted from the XML interface elements. This command construction process creates a direct pathway for buffer overflow exploitation.
The technical implementation of this vulnerability follows a precise sequence of operations that amplifies the security risk. The system extracts interface element names from XML files and directly passes them to sprintf() without proper length validation, creating a buffer that can be overflowed when interface values exceed 512 characters minus the command prefix length. The destination buffer sp+0x40 becomes overflowed with data from the interface element, and the subsequent strcpy() operation at address 0x1ea08 copies data from the overflowed buffer into adjacent memory at sp+0x440. This adjacent memory layout creates a scenario where the stack buffer lacks proper null termination, leading to memory corruption that can be exploited by attackers. The vulnerability is particularly concerning because it operates within a service that likely runs with elevated privileges in industrial control environments, making it a prime target for attackers seeking persistent access to critical infrastructure systems.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable complete system compromise within industrial environments. The WAGO PFC 200 devices are commonly deployed in critical infrastructure settings where maintaining system availability and security is paramount. Attackers who successfully exploit this vulnerability can cause the iocheckd service to crash, potentially leading to denial of service conditions that could affect industrial processes. More critically, the stack buffer overflow creates opportunities for code execution attacks that could allow malicious actors to gain unauthorized access to the control systems. The vulnerability's exploitation requires only sending a specially crafted packet to the device, making it accessible to remote attackers without physical access. This characteristic aligns with ATT&CK technique T1210 for exploiting vulnerabilities in remote services and represents a significant risk to operational technology environments. The vulnerability's presence in industrial control systems also violates security principles outlined in NIST SP 800-82 and other industrial cybersecurity frameworks, as it demonstrates inadequate input validation and memory management practices.
Mitigation strategies for CVE-2019-5186 should focus on immediate patching of affected WAGO PFC 200 devices through official firmware updates provided by the vendor. Network segmentation and access controls should be implemented to limit exposure of these devices to untrusted networks, particularly in industrial environments where they may be directly connected to operational technology networks. Input validation controls should be enhanced to prevent interface element names from exceeding safe length limits, and any custom XML parsing code should be reviewed for similar buffer overflow vulnerabilities. The vulnerability's classification under CWE-121 stack-based buffer overflow indicates that defensive programming practices such as using safe string functions like snprintf() instead of sprintf() would have prevented the issue. Additionally, implementing network monitoring and intrusion detection systems can help detect exploitation attempts targeting this specific vulnerability. Organizations should also consider implementing regular security assessments of industrial control systems to identify and remediate similar vulnerabilities that may exist in other proprietary software components. The attack surface reduction should include disabling unnecessary services and ensuring that only authorized personnel have access to configuration interfaces that process XML files.