A significant security flaw has been uncovered in grub2's NTFS file system driver, identified as CVE-2023-4693. This out-of-bounds read vulnerability could enable a physically present attacker to use a specially-crafted NTFS file system image to read arbitrary memory locations. Such an attack poses a serious risk to the confidentiality of sensitive data stored in memory caches or EFI variable values. This article aims to provide an overview of CVE-2023-4693, discussing the exploit details, relevant code snippets, and original references.

Exploit Details

Grub2, the widely-used bootloader in many Linux distributions, is susceptible to an out-of-bounds read vulnerability in its NTFS file system driver. Exploiting this flaw requires an attacker to have physical access to the targeted system to present a purposely-malformed NTFS file system image. Once successful, the attacker can gain unauthorized access to crucial information such as cached data, EFI variable values, and other sensitive details.

Code Snippet

The issue originates from improper handling of unexpected input in the 'read' function of the NTFS file system driver. A code snippet showcasing this vulnerability is provided below:

static grub_err_t
grub_ntfs_read (grub_file_t file, char *buf, grub_size_t len)
  // ...
  // other variable definitions

  for (; readlen < len; readlen += minlen)
    // ...
    // other code statements

    // The unsafe out-of-bounds read occurs due to insufficient boundary checks.
    grub_memcpy (buf, cbuf + cluster_ofs, minlen);
  // ....

The insufficient boundary checks in the 'grub_memcpy' function enable the out-of-bounds read, resulting in the unauthorized access to arbitrary memory locations.

Original References

1. Grub2 Official Website: https://www.gnu.org/software/grub/
2. NTFS-3G project page: https://www.tuxera.com/community/open-source-ntfs-3g/
3. CWE-125: Out-of-bounds Read: https://cwe.mitre.org/data/definitions/125.html
4. CVE-2023-4693 entry in NIST National Vulnerability Database: https://nvd.nist.gov/vuln/detail/CVE-2023-4693

Mitigation and Remediation

Currently, there is no known fix or workaround for this vulnerability. To minimize the risk associated with CVE-2023-4693, system administrators should take the following precautions:

Ensure that only authorized personnel have physical access to critical systems.

- Regularly update and monitor system firmware and software to address any newly-discovered security issues promptly.
- Implement a robust incident response process to detect and respond to potential security breaches in a timely manner.

Closing Thoughts

Grub2's out-of-bounds read flaw (CVE-2023-4693) in its NTFS file system driver presents a significant threat to the confidentiality of sensitive data cached in memory or stored as EFI variable values. System administrators and security professionals must be aware of this vulnerability and take appropriate measures to protect their systems from potential attacks.


Published on: 10/25/2023 18:17:41 UTC
Last modified on: 11/07/2023 04:22:50 UTC