In this blog post, we will discuss a recently discovered vulnerability, CVE-2024-53589, in the GNU objdump utility version 2.43. GNU objdump is a popular command-line tool that displays information about object files, which are binary files containing compiled code. This vulnerability is due to a buffer overflow in the handling of tekhex-format files in the BFD (Binary File Descriptor) library, utilized by objdump.

The Vulnerability's Background

GNU objdump is a powerful utility widely used by developers and analysts for inspecting and debugging binaries. It reads object files and displays information such as disassembled code, symbol tables, and other useful insights. GNU objdump supports a variety of binary formats, one of which is the tekhex format.

The vulnerability CVE-2024-53589 pertains specifically to objdump's handling of tekhex format files. The tekhex format is an older hexadecimal format that was often used in legacy systems to encode binary data. It is less prevalent today but still encountered in certain applications.

The vulnerability was introduced in the BFD library, which is a part of the GNU Binutils project, and it provides low-level support for manipulating various binary file formats. GNU objdump relies on the BFD library to process different file formats, including the tekhex format.

The Details of the Exploit

The buffer overflow vulnerability in the BFD library's handling of tekhex format files allows an attacker to craft a malicious tekhex file that, when processed by objdump, triggers a buffer overflow. This overflow can lead to memory corruption, crashes, or, in the worst case, arbitrary code execution.

The vulnerability arises from improper validation of input when parsing tekhex files. A specific part of the tekhex format that objdump must parse is the record length field. This field indicates the number of data bytes that follow in the record. The parser does not properly validate this value, which can lead to a buffer overflow when reading the subsequent data bytes.

Here is a code snippet from the BFD library where the vulnerability exists

static const struct tekhex_tok_struct *
read_tekhex (bfd *abfd)
{
  ...
  /* Read the length byte.  */
  sum = (sum + (input_line[lineptr] - '')) & xff;
  lineptr++;
  / * Calculate the number of bytes to be read based on length byte
     (input_line[lineptr-1]) * /
  maxchars = 2 * (input_line[lineptr - 1] - '') + lineptr;
  ...
  for (; lineptr <= maxchars; lineptr += 2)
  {
    ...
  }
}

The vulnerability occurs in the loop that reads bytes from the input line based on the length byte. The parser does not properly validate the length byte, leading to a possible buffer overflow.

How to Reproduce the Vulnerability

To reproduce the vulnerability, an attacker would create a malicious tekhex file with a crafted record length field that triggers the buffer overflow. An example of such a tekhex file can be found in this security advisory from the BinSec project (http://www.binsec.com/cve-2024-53589/2024-07-29-buffer-overflow.html).

Using this malicious tekhex file, the attacker could then invoke objdump with the crafted file as input:

$ objdump -x malicious_file.tek

Processing the malicious tekhex file triggers the buffer overflow in objdump, leading to potential memory corruption or other undesired behavior.

Mitigation Strategies and Patching

To mitigate this vulnerability, users should apply the patch provided by the GNU Binutils project (see the original patch here: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=cd7591087edaad38ba195a92795008a6a594c17). This patch properly validates the record length field when parsing tekhex files in the BFD library, preventing the buffer overflow.

Users should also ensure they are using the latest version of GNU objdump, which should include the patched BFD library.

Alternatively, users can avoid opening tekhex files with objdump if they are unsure of their origin or validity.

Conclusion

In this blog post, we discussed CVE-2024-53589, a buffer overflow vulnerability resulting from improper handling of tekhex format files in GNU objdump version 2.43. We explored the details of the exploit, how to reproduce it, and mitigation strategies.

By understanding the cause and impact of such vulnerabilities, developers and sysadmins can better protect their systems from potential exploits. It is essential to keep software up-to-date and be familiar with the latest security patches and advisories.

Timeline

Published on: 12/05/2024 20:15:22 UTC
Last modified on: 12/11/2024 17:15:20 UTC