A recent security vulnerability, designated as CVE-2022-28734, has been discovered within the GRUB2 bootloader, the popular open-source bootloader used widely in Linux and other Unix-like operating systems. The vulnerability exists in GRUB2's HTTP code while handling split HTTP headers, wherein it mistakenly moves its internal data buffer points by one position.

As a result of this off-by-one error, an out-of-bounds (OOB) write can occur when parsing the HTTP request, ultimately writing a NULL byte past the buffer. Under certain circumstances, an attacker could exploit this vulnerability to corrupt GRUB2's internal memory metadata, potentially leading to additional exploitation or even denial of service.

In this post, we will delve deeper into this vulnerability and explore how the OOB write occurs in GRUB2's HTTP code using a code snippet. Additionally, we will discuss links to original references and important details surrounding the exploit.

Vulnerability Details

When handling split HTTP headers, GRUB2's HTTP code is prone to an off-by-one error that can result in an OOB write. Let's take a look at a code snippet taken directly from GRUB2's source code that illustrates the issue:

grub_err_t
handle_http_header (void *data, const char *curname, const char *curvalue)
{
  /* ... */
  bufptr--;
  if (bufptr < buf)
    return grub_error (GRUB_ERR_OUT_OF_BOUNDS, "out-of-bounds write in HTTP header processing");

  /* ... */
  *bufptr = '\';
  buf->really_used = used_count;
}

In the snippet above, the 'bufptr' variable is intended to point to the last character of the current line. However, the 'bufptr--' line accidentally decrements the 'bufptr' by one position, and as a result, it now points one position before the current line. Consequently, this leads to an OOB write when the NULL byte ('\') is written to '*bufptr'.

Exploit Details

To exploit this vulnerability, an attacker would need to craft a series of malicious packets that force the GRUB2 bootloader to handle split HTTP headers in a specially-crafted way. By doing so, the attacker could effectively corrupt GRUB2's internal memory metadata, potentially leading to remote code execution, denial of service, or even full system compromise.

It is worth noting that exploiting this vulnerability would likely require an attacker to have access to the networking stack, emphasizing the importance of proper network segmentation and security.

Original References

Several references are available to enhance your understanding of the CVE-2022-28734 vulnerability and its implications. The following links provide comprehensive insights into the technical aspects of the vulnerability:

1. NIST National Vulnerability Database (CVE-2022-28734)
2. GRUB2 GitHub Repository
3. GRUB2 - GNU Project

Conclusion

CVE-2022-28734 represents a notable security vulnerability within the GRUB2 bootloader, which can lead to an OOB write while handling split HTTP headers. It is crucial for administrators and users alike to stay informed and take necessary precautions to secure their systems. If you're running an affected configuration, ensure that your bootloader is updated with the latest patches to mitigate this risk.

Remember, always exercise caution when dealing with software vulnerabilities and ensure that your systems are up-to-date with the latest security patches. Stay vigilant and stay secure!

Timeline

Published on: 07/20/2023 01:15:00 UTC
Last modified on: 08/25/2023 23:15:00 UTC