CVE-2017-20156

Step 1: Payload Delivery: The attacker crafts a malicious URL containing a command injection payload. This payload is designed to execute arbitrary commands on the server. Step 2: Request Submission: The attacker sends the crafted URL to the Exciting Printer application. Step 3: Input Processing: The application receives the URL and processes it, likely extracting the URL argument from the request. Step 4: Vulnerable Function Call: The prepare_page.rb file is invoked, and the extracted URL is passed to a function that uses it in a system command. Step 5: Command Execution: Due to the lack of proper input validation, the attacker's injected commands are executed on the server. Step 6: System Compromise: The attacker gains control of the server, potentially leading to data exfiltration, further exploitation, or denial-of-service.

The vulnerability stems from improper sanitization and validation of user-supplied input within the prepare_page.rb file, specifically when handling the URL argument. The application fails to adequately sanitize the input before passing it to a system command, allowing an attacker to inject arbitrary commands. The root cause is a lack of input validation and output encoding, leading to command injection. The code likely uses the user-provided URL in a system call, such as system() or exec(), without proper escaping or quoting, making it susceptible to command injection. The patch 5f8c715d6e2cc000f621a6833f0a86a673462136 likely addresses this by implementing input validation, sanitization, and potentially escaping the user-provided URL before using it in any system calls.