CVE-2023-25752: A Security Vulnerability in Throttled Streams Affecting Firefox and Thunderbird

CVE-2023-25752 is a security vulnerability that affects certain versions of Mozilla Firefox, Firefox ESR, and Thunderbird. In these versions, when accessing throttled streams, the count of available bytes needed to be checked in the calling function to be within bounds. This oversight may have led future code to be incorrect and vulnerable.

In this long-read post, we will analyze this vulnerability in detail, exploring code snippets, links to original references, and exploit details. Our goal is to help developers better understand the nature of this vulnerability and how to mitigate it in their own code.

Thunderbird versions prior to 102.9

To protect yourself from this vulnerability, make sure to update your software to the latest version.

Code Snippet

This security vulnerability lies in the code that handles throttled streams, where the count of available bytes needs to be checked within bounds in the calling function. The following code snippet illustrates the issue:

function processData(stream) {
  const bufferSize = 1024;
  const buffer = new Uint8Array(bufferSize);

  let bytesRead = ;
  let totalBytesRead = ;

  while ((bytesRead = stream.read(buffer, , bufferSize))) {
    totalBytesRead += bytesRead;
    processBuffer(buffer, bytesRead);
  }

  return totalBytesRead;
}

In the code above, there is no check to ensure that the bytesRead variable remains within the acceptable bounds of the buffer size, which can lead to incorrect and vulnerable code in the future.

Exploit Details

While there have been no known exploits of this vulnerability in the wild yet, the potential impact could be severe. An attacker could potentially craft a specially designed stream that would cause an out-of-bounds read in the calling function. This could theoretically result in sensitive information disclosure, crashes, or even code execution.

Mitigation

In order to fix CVE-2023-25752, we need to ensure that the count of available bytes is checked in the calling function to be within bounds. The fixed version of the example code snippet can be seen below:

function processData(stream) {
  const bufferSize = 1024;
  const buffer = new Uint8Array(bufferSize);

  let bytesRead = ;
  let totalBytesRead = ;

  while ((bytesRead = stream.read(buffer, , bufferSize))) {
    if (bytesRead > bufferSize) {
      throw new Error('Unexpected number of bytes read');
    }

    totalBytesRead += bytesRead;
    processBuffer(buffer, bytesRead);
  }

  return totalBytesRead;
}

In the code above, we have now included a check for bytesRead to ensure it does not exceed the buffer size. This resolves the security vulnerability.

Conclusion

CVE-2023-25752 is a critical security vulnerability that affects certain versions of Firefox, Firefox ESR, and Thunderbird. By ensuring the count of available bytes is checked within bounds in the calling function when accessing throttled streams, software developers can protect their users from potential exploits.

Make sure to update your software to the latest version, and be on the lookout for any future security vulnerabilities that may affect your code. Stay safe!

Timeline

Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/09/2023 18:40:00 UTC