CVE-2017-14855

Step 1: Target Identification: Identify a Red Lion HMI panel accessible via HTTP. This requires network scanning and reconnaissance. Step 2: Request Construction: Craft an HTTP POST request. The request's URI should be a very long, non-existent path (e.g., / followed by a large number of characters). Step 3: Payload Delivery: Send the crafted HTTP POST request to the target HMI panel. Step 4: Vulnerability Trigger: The HMI panel's HTTP server processes the request. Due to the long URI, a buffer overflow or other memory corruption occurs. Step 5: Denial of Service: The memory corruption causes a software exception, crashing the HTTP server and resulting in a denial of service. The HMI panel becomes unresponsive to HTTP requests.

The vulnerability stems from inadequate input validation and error handling within the Red Lion HMI's HTTP server. Specifically, the server fails to properly handle extremely long URI strings in POST requests. When a request with a URI exceeding the allocated buffer size is received, it leads to a buffer overflow or other memory corruption issues. This, in turn, causes a software exception, crashing the HMI's HTTP server and leading to a DoS condition. The root cause is a lack of bounds checking on the URI length before processing the request, allowing an attacker to overwrite critical memory regions. The software exception is likely triggered by an attempt to access or write to an invalid memory address after the buffer overflow.