CVE-2024-12133 - Dissecting the Vulnerability in libtasn1 Inefficient Certificate Data Processing Leading to DOS Attacks

In this long read post, we will analyze a recently discovered vulnerability known as CVE-2024-12133, which affects libtasn1, a widely used library for managing Abstract Syntax Notation One (ASN.1) structures. Specifically, this vulnerability relates to the inefficient handling of certificate data, leading to potential denial of service (DoS) attacks. We will provide a deep dive into the details of this flaw, including code snippets, original references, and information on how an attacker could exploit the issue.

Vulnerability Details

CVE-2024-12133 affects libtasn1, an essential component of many Linux distributions and secure communication frameworks. The problem lies in the library's parsing of certificates with large numbers of elements. Due to the inefficient handling of this specific certificate data, the libtasn1 library takes significantly longer than expected to process, potentially slowing down or even crashing the system. This vulnerability can be exploited by an attacker sending a specially crafted certificate that would cause a denial of service (DoS) attack.

Code Snippet

Below is a code snippet that demonstrates the issue of inefficient handling of certificate data in libtasn1:

int _asn1_extract_der_octet (ASN1_TYPE node)
{
  /* ... */
  for (k = 1; k < len2; k++) // Loop through elements in the certificate
  {
    result = _asn1_octet_der (node2, der, &len3);
    if (result != ASN1_SUCCESS)
      {
        _asn1_free_der (der);
        return result;
      }
    der_len += len3; // This operation has to be done for a large number of elements and gets inefficient
    /* ... */
  }
  /* ... */
}

The primary issue here is the inefficient processing of a large number of elements in a certificate. The code snippet above shows a loop that iterates through each element and adds its length (len3) to the total length (der_len). This operation is performed for every element in the certificate, resulting in slow processing and potentially causing the system to crash due to excessive resource consumption.

Original References

The issue was initially reported on the libtasn1 mailing list. Here are a few valuable references related to CVE-2024-12133:

1. Initial disclosure of the vulnerability on the libtasn1 mailing list
2. CVE-2024-12133 entry on the National Vulnerability Database (NVD)
3. Libtasn1 source code on GitHub

Exploit Details

To exploit this vulnerability, an attacker would first need to generate a malicious certificate containing a large number of elements. By carefully crafting the certificate and sending it to an affected system, the attacker could induce a denial of service (DoS) attack.

Suppose an application uses the libtasn1 library to parse incoming certificates during secure communications (e.g., TLS connections) and can process a certificate containing a large number of elements. In that case, an attacker could send the malformed certificate to consume the system's resources, ultimately making the service unavailable or even crashing it.

Mitigation

To fix this vulnerability, it is crucial to update the libtasn1 library to a version that addresses the inefficient processing of certificate data. Patched releases of libtasn1 incorporate performance optimizations and additional security checks to prevent DoS attacks due to excessive resource consumption.

In conclusion, CVE-2024-12133 is a severe vulnerability in the libtasn1 library that could allow an attacker to initiate a denial of service (DoS) attack. By understanding the technical details behind this issue and promptly applying necessary updates and patches, system administrators, and developers can protect their systems from potential exploitation.

Timeline

Published on: 02/10/2025 16:15:37 UTC