CVE-2023-36328: Exploring the Integer Overflow Vulnerability in mp_grow in libtom libtommath before commit beba892bcd4e4ded4d667ab1d2a94f4d75109a9

The CVE-2023-36328 is an Integer Overflow vulnerability that affects the mp_grow function in the libtom libtommath library before the commit beba892bcd4e4ded4d667ab1d2a94f4d75109a9. This vulnerability can be exploited by an attacker to execute arbitrary code and cause a denial of service (DoS) on the target system. In this post, we will dive deep into this vulnerability, investigate the code snippets, and explore the exploit details with original references to help you understand the issue and protect your systems from this vulnerability.

Code Snippet

The vulnerability exists in the mp_grow function, which is responsible for ensuring that enough memory is available for a multiple precision integer. Here's the problematic code snippet from the libtom libtommath library:

// file: bn_mp_grow.c

int mp_grow(mp_int *a, int size)
{
  int     i;
  mp_digit *tmp;

  // Make sure there are enough digits
  if (size <= a->alloc) {
    return MP_OKAY;
  }

  // Increase the number of digits available
  if (a->alloc == ) {
    a->alloc      = size;
    a->dp         = OPT_CAST(mp_digit) XMALLOC((size_t)a->alloc * sizeof(mp_digit));
 } else {
    tmp = a->dp;
    a->dp = OPT_CAST(mp_digit) XREALLOC(tmp, (size_t)size * sizeof(mp_digit));
 }

  // In case of memory allocation failure
  if (a->dp == NULL) {
    return MP_MEM;
  }

  // Zero the digits
  for (i = a->used; i < size; i++) {
    a->dp[i] = ;
  }

  // Update the allocated size
  a->alloc = size;

  return MP_OKAY;
}

The issue is caused due to improper handling of integer overflows, allowing an attacker to execute arbitrary code or cause a DoS.

Exploit Details

The exploit takes advantage of the integer overflow in the multiplication operation (size_t)size * sizeof(mp_digit) within the memory allocation functions XMALLOC and XREALLOC. By carefully crafting the size variable in such a way that the (size_t)size * sizeof(mp_digit) multiplication overflows and causes memory corruption, an attacker can execute arbitrary code or cause a denial of service.

This vulnerability particularly affects applications that use libtom libtommath to process untrusted input, as they may be affected by the DoS or remote code execution attacks due to the improper handling of integer overflows.

In addition, the applications that perform mathematical operations using libtom libtommath may also be at risk of incorrect results or crashes due to memory corruption, thus impacting their reliability.

Original References

The vulnerability was initially reported by GitHub user @ikelos in this issue on GitHub. The fix for this vulnerability can be found in the following commit: beba892bcd4e4ded4d667ab1d2a94f4d75109a9.

Mitigation

To protect your systems and applications from this vulnerability, you should update your libtom libtommath library to the latest version or apply the patch from the aforementioned commit. This will ensure that your applications are safe from this integer overflow vulnerability and the potential threats associated with it.

Conclusion

The CVE-2023-36328 vulnerability exposes libtom libtommath users to potential remote code execution and denial of service attacks due to an integer overflow in the mp_grow function. By understanding the vulnerability, reviewing the code snippet, and exploring the exploit details, developers and system administrators can take the appropriate steps to update their systems and protect their applications from this critical security vulnerability.

Timeline

Published on: 09/01/2023 16:15:08 UTC
Last modified on: 11/07/2023 04:16:32 UTC