Common Vulnerabilities and Exposures (CVE) identifier CVE-2024-2757 refers to a security vulnerability found in PHP (a popular scripting language for web development) versions 8.3. up to, but not including, 8.3.5. This vulnerability involves a potential Denial of Service (DoS) attack through the PHP function mb_encode_mimeheader().

In this post, we will dive deep into the nature of this vulnerability, demonstrate a code snippet with an example, provide links to the related official references, and discuss potential exploit details. By the end of this post, you will have an understanding of CVE-2024-2757 and the importance of updating your PHP applications to the latest secure version.

Vulnerability Details

The vulnerability in question is specific to the PHP function mb_encode_mimeheader(), which is a part of the Multibyte String (mbstring) extension. This extension is commonly used in PHP applications to handle non-ASCII character sets in strings, which may be required for various email applications, file handling, or other uses.

For certain inputs, mb_encode_mimeheader() could potentially enter an endless loop (i.e., an infinite loop) if it encounters an unusually long string of non-space characters followed by a space. As the function will not terminate when faced with such inputs, it leaves the affected application vulnerable to a potential DoS attack, should a malicious user intentionally send such input data.

To put it simply, this vulnerability could allow an attacker to overuse the resources of a server or an application (such as CPU and memory) by exploiting the endless loop in the mb_encode_mimeheader() function, rendering the affected application unresponsive or leading to a crash.

Below is a basic PHP script that uses the mb_encode_mimeheader() function

<?php
// Set the input string with specific data that triggers the endless loop
$input = str_repeat('A', 998) . " ";

// Call the mb_encode_mimeheader() function with the input string
$header = mb_encode_mimeheader($input);

// Print the encoded header
echo $header;
?>

In this code snippet, the $input variable is assigned a string composed of 998 'A' characters followed by a space. As mentioned earlier, this particular input string may cause the mb_encode_mimeheader() function to run endlessly.

Exploit Details

To perform the DoS attack, an attacker would create and send a request with a crafted payload containing long, continuous strings of non-space characters followed by a space character, targeting an application that uses the vulnerable mb_encode_mimeheader() function. As a result, the affected server or application will get stuck in the endless loop and consume excessive resources until it crashes or becomes unresponsive.

It is important to note that this exploit may not be effective against all PHP applications. The impact will depend on the specific implementation of the function in each case. Regardless, it is always a best practice to update your PHP applications to the latest secure version to minimize risks associated with known vulnerabilities like CVE-2024-2757.

For more information about CVE-2024-2757, please refer to the following official sources

- PHP.net Bug Tracker Entry for CVE-2024-2757
- National Vulnerability Database Entry for CVE-2024-2757

Conclusion

In conclusion, CVE-2024-2757 is a noteworthy vulnerability in PHP versions 8.3.* prior to 8.3.5. The mb_encode_mimeheader() function's potential to enter an endless loop when processing specific inputs makes affected applications susceptible to DoS attacks. To mitigate this vulnerability, it is highly recommended that you upgrade your PHP applications to the latest secure version (8.3.5 or newer).

As a PHP developer or an application administrator, understanding the risks associated with known vulnerabilities, such as CVE-2024-2757, is crucial to maintaining the security of your applications and infrastructure. Stay informed and up-to-date with the latest vulnerability reports and updates to keep your web applications as secure as possible.

Timeline

Published on: 04/29/2024 04:15:08 UTC
Last modified on: 07/03/2024 01:53:32 UTC