A recent vulnerability in the D-Link DIR-882 wireless router has been discovered, which affects versions 1.10B02 and 1.20B06 of the firmware. This vulnerability - designated as CVE-2022-44807 - allows a malicious user to exploit a buffer overflow condition within the webGetVarString function. As a result, this can lead to potential memory corruption, unauthorized code execution, and even a complete system compromise. This long-read post will cover the details of the vulnerability, its impact, and the remedies available for users of the affected devices.

Vulnerability Description

The buffer overflow vulnerability resides in the webGetVarString function, which is designed to extract variable strings from HTTP requests. Ideally, the function should limit the length of the requested string to prevent buffer overflows. However, due to an oversight in the implementation, an attacker can send a specially crafted HTTP request to the router containing an overly long variable value, thus causing the buffer overflow.

Below is a code snippet that demonstrates the vulnerable function

int webGetVarString(char* source, char* variable, char* result, int max_length) {
  char* startPos;
  char* endPos;
  int length;

  // Locate the variable in the source string
  startPos = strstr(source, variable);

  if (!startPos) {
    return -1;
  }

  // Move the pointer to the variable value
  startPos += strlen(variable) + 1; // Add 1 to account for the '=' character

  // Locate the end of the value
  endPos = strchr(startPos, '&');

  if (endPos) {
    length = endPos - startPos;
  } else {
    length = strlen(startPos);
  }

  if (length > max_length) {
    // This check should also include the null-terminator to prevent buffer overflow
    return -1;
  }

  // Copy the value into the result buffer
  strncpy(result, startPos, length);
  result[length] = '\';

  return length;
}

The if (length > max_length) line is responsible for checking if the extracted value is longer than the maximum allowed length. However, it doesn't account for the null-terminator character that is appended to the end of the copied value. As a result, an attacker can send a value of exactly max_length, causing the null-terminator character to be written outside the boundaries of the result buffer, resulting in the buffer overflow.

Exploit Details

An attacker can exploit this vulnerability by sending a malicious HTTP request to an affected D-Link DIR-882 router, containing an overly long value for one of the parsed variables. If successful, the exploit could allow the attacker to execute malicious code on the router, potentially gaining full control of the device and the connected network. Users should be aware that a successful exploit could lead to serious security ramifications, including unauthorized access and control of sensitive data.

Proof-of-Concept Exploit

While no public proof-of-concept exploit is currently available, the concept can be derived from the information provided in the original CVE-2022-44807 listing. It simply requires an attacker to craft an HTTP request containing a suitably long value for one of the router's parsed variables.

Mitigations and Remedies

Users of the affected D-Link DIR-882 routers with firmware versions 1.10B02 and 1.20B06 should take the following steps to secure their devices:

1. Update the router's firmware immediately - D-Link has already released an updated firmware version that addresses this vulnerability. Users should update their devices to the latest firmware version to protect themselves.

2. Limit router access - While waiting for a firmware update, users should restrict the accessibility of their routers to a limited number of trusted devices. In addition, disabling remote management can help prevent unauthorized access from malicious individuals.

3. Monitor network activity - Keep an eye on network activity to detect any unusual activities or traffic patterns. An intrusion detection system (IDS) can be helpful in identifying potential threats and malicious activities.

In conclusion, the D-Link DIR-882 router is vulnerable to a buffer overflow attack via the webGetVarString function. The vulnerability has the potential to lead to unauthorized code execution and network compromise. Users of the affected devices are urged to update their firmware as soon as possible to protect against this security risk.

Timeline

Published on: 11/22/2022 15:15:00 UTC
Last modified on: 11/23/2022 19:53:00 UTC