In this article, we'll discuss a Common Vulnerabilities and Exposures (CVE) entry, CVE-2023-29400. We'll take a look at a code snippet, potential exploit details, and original references about this vulnerability. This vulnerability affects templates containing actions in unquoted HTML attributes, where output with unexpected results may be generated when parsed due to HTML normalization rules, allowing injection of arbitrary attributes into tags.

Vulnerable code might look like

<!DOCTYPE html>
<html>
<head>
  <title>Example Page</title>
</head>
<body>
  <form action="/submit" method="POST">
    <input type="text" name="username" placeholder="Username" title={{.}}>
    <button type="submit">Submit</button>
  </form>
</body>
</html>

In this example, the title attribute of the input element contains an unquoted action {{.}}. When executed with empty input, this can result in an output with unexpected results due to HTML normalization rules.

Exploit Details

When an attacker provides input that injects arbitrary attributes into tags, it may allow them to perform various attacks like cross-site scripting (XSS) and exfiltration of sensitive information.

For the given code snippet, an attacker may provide an input that closes the "title" attribute and injects the "onmouseover" attribute with a JavaScript payload:

Input: }}" onmouseover="alert('XSS Attack')"

The resulting HTML becomes

<input type="text" name="username" placeholder="Username" title="}}" onmouseover="alert('XSS Attack')">

Visitors to the site will see an alert pop up with the message "XSS Attack" when they mouse-over the input field. This is a simple example that demonstrates how an attacker can exploit this vulnerability and run arbitrary JavaScript code in the context of the targeted website.

Mitigation

To mitigate this vulnerability, it is recommended to always quote HTML attribute values and ensure user input is properly sanitized and escaped before being embedded into the HTML DOM.

In the example above, the following changes should be made

<input type="text" name="username" placeholder="Username" title="{{.}}">

OWASP - Unquoted HTML Attributes

https://owasp.org/www-project-web-security-testing-guide/assets/archive/OWASP_Testing_Guide_v4.pdf (Page 138)

HTML Standard - HTML Syntax

https://html.spec.whatwg.org/multipage/syntax.html#syntax-attributes

OWASP - Cross-site Scripting (XSS)

https://owasp.org/www-community/attacks/xss/

For a comprehensive understanding of CVE-2023-29400 and the implications of this vulnerability, it is recommended to review these references.

Conclusion

CVE-2023-29400 is a vulnerability that affects templates containing actions in unquoted HTML attributes. Exploiting this flaw allows an attacker to inject arbitrary attributes into tags, enabling them to perform various attacks on a victim's website. To mitigate this issue, developers must always quote HTML attribute values and thoroughly sanitize user input before embedding it into the HTML DOM.

Timeline

Published on: 05/11/2023 16:15:00 UTC
Last modified on: 05/22/2023 18:21:00 UTC