CVE-2023-24540: JavaScript Whitespace Character Vulnerability in Template Sanitization

A recently discovered vulnerability, identified as CVE-2023-24540, suggests that not all valid JavaScript whitespace characters are being considered as whitespace during the sanitization process of certain templates containing actions. This vulnerability could potentially allow attackers to execute malicious code by circumventing the sanitization process of these templates. In this article, we will dive into the details of this vulnerability, including the affected environment, implications of the vulnerability, and available workarounds or patches.

Code Snippet

The character set that is considered valid whitespace for JavaScript includes the following characters: "\t", "\n", "\f", "\r", "\u002", "\u2028", and "\u2029". However, CVE-2023-24540 arises when templates have additional JavaScript valid whitespace characters which are outside this character set. This issue arises when these templates also contain actions that need to be sanitized during execution.

The following code snippet illustrates a scenario where this vulnerability could be exploited

<script>
  let sampleTemplate = `
    <div onclick="executeMaliciousCode()">
      Harmless content
    </div>
  `;
  function sanitizeTemplate(template) {
    // ...Some sanitization logic...
  }
  function executeMaliciousCode() {
    // ...Malicious code execution...
  }

  let sanitizedTemplate = sanitizeTemplate(sampleTemplate);
  document.body.innerHTML = sanitizedTemplate;
</script>

In this code snippet, additional JavaScript whitespace characters might not be properly sanitized, potentially allowing the executeMaliciousCode() function to pass through and inject malicious code when rendering the sanitizedTemplate.

The vulnerability has been disclosed in the following sources

- National Vulnerability Database (NVD) entry: CVE-2023-24540
- Vulnerability Research Publication: Details about the discovery of CVE-2023-24540

Templates that include JavaScript actions that should be sanitized during execution.

Exploiting this vulnerability can lead to unauthorized execution of malicious code, potentially causing harm to the users and the system. The attacker may also be able to compromise sensitive data by injecting unauthorized code execution through unsanitized templates.

Mitigations and Patches

Currently, there is no full patch available that addresses this vulnerability, but an important mitigation technique is to ensure the proper handling of all valid JavaScript whitespace characters during the template sanitization process. You can achieve this by:

Modifying the sanitization function to cover all valid JavaScript whitespace characters.

- Leveraging a third-party library, such as DOMPurify, to handle HTML sanitization with sufficient coverage for JavaScript whitespace characters.

Conclusion

The CVE-2023-24540 vulnerability highlights the importance of thorough sanitization and secure coding practices within JavaScript applications. As a developer, you should always ensure your templates are sanitized effectively and stay up to date with the latest security updates and patches. While the full patch for CVE-2023-24540 is not available yet, the mitigation strategies mentioned above can help you protect your applications from unauthorized code execution.

Timeline

Published on: 05/11/2023 16:15:00 UTC
Last modified on: 05/22/2023 18:22:00 UTC