CVE-2024-35333: Uncovering a Stack-Buffer-Overflow Vulnerability in html2xhtml 1.3's read_charset

CVE-2024-35333 highlights a critical stack-buffer-overflow vulnerability present in html2xhtml 1.3's read_charset_dec function. In this post, we will walk through the technical details of this vulnerability, how it can be exploited, and its potential consequences. Additionally, we'll share code snippets and links to original references for a deeper understanding. Let's dive in!

Background

html2xhtml is a utility for converting HTML to XHTML. It has a function called read_charset_decl that is responsible for parsing an HTML file's character set declaration. It is particularly susceptible to a stack-buffer-overflow vulnerability due to improper bounds checking while copying data into a fixed-size stack buffer.

The vulnerability occurs in the read_charset_decl function in the following segment of code

char buf[256];
/* ... */
fgets((char*)buf, 1024, f);

As shown, the function reads up to 1024 bytes of input data into a buffer with a fixed size of 256 bytes. This creates a buffer overflow, which can lead to several dangerous consequences, such as arbitrary code execution, denial-of-service, or data corruption.

Exploitation

An attacker can take advantage of this vulnerability by providing a specially crafted input file to the vulnerable html2xhtml utility. With careful crafting of the input, the attacker can overwrite important areas of the stack and manipulate the program's control flow.

Here's an example of a malicious input that triggers the vulnerability

<!DOCTYPE html>
<html>
<head>
  <meta charset="aaaaaaaaaaaaaaaaaaaaaaaaa...[up_to_1024_bytes]...aaaaaa">
</head>
<body>
Hello, world!
</body>
</html>

Upon parsing this file with html2xhtml, the read_charset_decl function will exhibit the stack-buffer-overflow vulnerability.

Mitigation

As of now, there is no official patch available for this vulnerability. However, users can patch the source code themselves by applying proper bounds checking before copying data into the buffer. Replace the vulnerable code:

fgets((char*)buf, 1024, f);

with a safer alternative

fgets((char*)buf, sizeof(buf), f);

This change ensures that the buffer only receives data within its allocated size, protecting against the buffer overflow exploitation.

The following resources provide more information on the CVE-2024-35333 vulnerability

1. Vulnerability disclosure
2. html2xhtml project page

Conclusion

CVE-2024-35333 is a severe stack-buffer-overflow vulnerability within html2xhtml 1.3's read_charset_decl function. By sending a specially crafted input to the vulnerable utility, an attacker can exploit this issue to execute arbitrary code, cause denial of service, or corrupt data. We recommend all users apply the suggested mitigation and keep a close eye on future patches to resolve this vulnerability.

Timeline

Published on: 05/29/2024 16:15:11 UTC
Last modified on: 08/19/2024 16:35:15 UTC