Hello, fellow cybersecurity enthusiasts! Today, I would like to bring your attention to a recently discovered vulnerability: CVE-2024-8938. This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), and it could lead to severe consequences if exploited. Devices that communicate using the Modbus protocol are at risk of falling victim to a potential Man-In-The-Middle (MITM) attack, followed by arbitrary code execution if a maliciously crafted Modbus function call is sent to the target device. In simpler terms, this means an attacker could potentially hijack the communication between two Modbus devices and execute their code by exploiting this vulnerability!

Exploit Details

Before we dive into the exploit details, let's briefly discuss what CWE-119 means, as it is crucial to understand the vulnerability. CWE-119 pertains to memory buffer issues that happen when a program fails to limit operations within the bounds of allocated memory. This can cause memory corruption, crashes, or even execute arbitrary code—the worst possible outcome for any system.

In the case of CVE-2024-8938, the vulnerability lies in the improper handling of the memory buffer in devices that use the Modbus protocol for communication. An attacker who is well-versed in carrying out MITM attacks could intercept, modify or inject malicious Modbus function calls, making changes to the memory area involved in memory size computation. This could lead to an attacker executing their code on the compromised device.

To illustrate the exploit, let's have a look at the following code snippet

int modbus_process_request(uint8_t* request, uint8_t* response) {
  uint8_t function_code = request[1];
  uint16_t address = (request[2] << 8) | request[3];
  uint16_t size = (request[4] << 8) | request[5];
  ...
}

In the above code, the modbus_process_request function processes the incoming Modbus request, including function_code, address, and size values. However, it does not verify if the size value is within the bounds of the allocated memory buffer. An attacker could craft a malicious Modbus function call with an unusually large size value to manipulate the memory buffer, possibly allowing them to execute arbitrary code.

Mitigation

To prevent falling victim to this vulnerability, it is crucial to implement proper checks and validation when processing Modbus requests. The code snippet below showcases an example of how to include these checks:

uint16_t valid_range = sizeof(memory_buffer); // Maximum valid range or length based on memory buffer size

int modbus_process_request(uint8_t* request, uint8_t* response) {
  uint8_t function_code = request[1];
  uint16_t address = (request[2] << 8) | request[3];
  uint16_t size = (request[4] << 8) | request[5];

  // Validate size and address to ensure it is within the bounds of memory buffer
  if (size <= valid_range && (address + size) <= valid_range) {
    ...
  }
  ...
}

The vulnerability has been publicly disclosed, and the responsible manufacturers are working to release patches for the affected devices. As a user, it is crucial to keep your device firmware up-to-date and apply security patches as soon as available. Additionally, network operators should isolate and secure Modbus traffic to prevent MITM attacks and potential exploitation.

- Original CVE Report: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-8938
- CWE-119 Details: https://cwe.mitre.org/data/definitions/119.html
- Modbus Protocol Official Website: http://www.modbus.org/

Wrap-up

In conclusion, CVE-2024-8938 is a severe vulnerability that poses a significant risk to devices that use the Modbus protocol. By carrying out a MITM attack and sending a crafted Modbus call to vulnerable devices, an attacker can potentially execute arbitrary code. To prevent this, it is essential to stay vigilant and keep devices up-to-date with the latest security patches. Ensure proper checks and validations are in place to prevent arbitrary code execution and protect your valuable assets. Stay safe and secure!

Timeline

Published on: 11/13/2024 05:15:25 UTC
Last modified on: 11/13/2024 17:01:16 UTC