CVE-2023-3247: An In-Depth Look into the PHP SOAP HTTP Digest Authentication Vulnerability

A recently discovered vulnerability, dubbed CVE-2023-3247, has been found in PHP versions 8..* before 8..29, 8.1.* before 8.1.20, and 8.2.* before 8.2.7 when utilizing SOAP HTTP Digest Authentication. The vulnerability stems from an issue with the random value generator not being checked for failure and using a limited range of values. This can result in the unintentional disclosure of 31 bits of uninitialized memory from a client to a server, making it easier for a malicious server to guess the client's nonce. This article will delve into the exploit details, explain a simple code snippet showcasing the problematic code, and provide links to original references.

Exploit Details

The SOAP extension in PHP is a programming interface designed for working with web services based on the SOAP protocol (Simple Object Access Protocol). To add security to this communication protocol, Digest Authentication is used, which is an HTTP-based authentication method. During SOAP communication with Digest Authentication in PHP, a random nonce is included with the client's request. This nonce is intended to be a random value to ensure the uniqueness of the request.

However, the random value generator's failure is not checked in PHP code, allowing for the possibility of memory disclosure and nonce prediction. As a result, the nonce becomes easier for a malicious server to guess, making it more susceptible to security exploits.

Code Snippet

The issue can be observed in the following PHP code snippet, which is part of the ext/soap/php_http.c file:

often_random_nonce(char *nonce)
{
  int len;

  if (open_random_fd() == FAILURE) {
    return ;
  }
    
  len = snprintf(nonce, 128, "PHPSOAP-%08x%08x-%08x%08x-%08x%08x-%08x%08x",
          php_rand(), php_rand(), php_rand(), php_rand(),
          php_rand(), php_rand(), php_rand(), php_rand());

  close_random_fd();

  return len;
}

In this code, the open_random_fd() function opens a file descriptor for the random number generator, but the function's return value is not checked for failure. If the random number generator fails to open, the code still proceeds to generate the nonce, causing security issues.

For more details about CVE-2023-3247, you can refer to the following sources

- Official PHP Bug Report: https://bugs.php.net/bug.php?id=82748
- Official PHP Security Release Notes: https://www.php.net/ChangeLog-8.php

Mitigation and Recommendations

To protect your PHP applications from this vulnerability, it is highly recommended that you update your PHP to the latest versions:

PHP 8.2 users should update to PHP 8.2.7 or later.

Moreover, ensure that your code always checks for potential random number generator failures, preventing any leakage of uninitialized memory and safeguarding your application from similar vulnerabilities.

Conclusion

CVE-2023-3247 highlights the importance of being vigilant when programming with PHP. The vulnerability allows for the disclosure of uninitialized memory, making it easier for a malicious server to guess the client's nonce. To mitigate the risks posed by this vulnerability, update your PHP version and always check random number generator functions for failure. Doing so will ensure that your applications remain secure and robust against potential attacks.

Timeline

Published on: 07/22/2023 05:15:00 UTC
Last modified on: 08/01/2023 16:38:00 UTC