CVE-2024-6197 - Libcurl ASN.1 UTF8 String Parser Memory Corruption Vulnerability

A vulnerability (CVE-2024-6197) has been discovered in the ASN.1 UTF-8 string parser function (utf8asn1str) of the libcurl library. This vulnerability could potentially lead to memory corruption and remote code execution on affected systems. In this long-read post, we will delve into the technical details of the vulnerability, its consequences, and possible exploitation scenarios. We will also provide code snippets demonstrating the issue and links to original references for further study.

Vulnerability Details

The vulnerability resides in the utf8asn1str() function of libcurl's ASN.1 parser. The function is responsible for parsing an ASN.1-formatted UTF-8 string and detecting any invalid fields in the input data, upon which it returns an error. However, when an invalid field is encountered, the function erroneously frees a 4-byte local stack buffer.

static int utf8asn1str(const char *data, size_t length) {
  ...
  if(some_condition) {
    /* Invalid field detected */
    free(local_buffer);
    return error;
  }
}

Most modern memory allocation implementations (malloc) will detect this erroneous call and immediately abort the process. However, some implementations will accept the invalid pointer and add the memory to their list of available memory chunks.

This behavior can lead to the overwriting of nearby stack memory. The content of the overwritten memory is determined by the free() implementation – most commonly memory pointers and a set of flags. The primary consequence of exploiting this vulnerability is a crash, although more severe outcomes cannot be ruled out in specific circumstances.

Exploitation

Exploiting the CVE-2024-6197 vulnerability could allow an attacker to corrupt memory on an affected system. By carefully crafting malicious input data, an attacker might trigger the erroneous freeing of a 4-byte local stack buffer in the utf8asn1str() function. This could lead to memory corruption and, ultimately, control over the execution flow of the vulnerable process.

Due to the unpredictable nature of memory corruption vulnerabilities, the likelihood of successfully exploiting this bug varies depending on the target application and system, memory layout, and specific memory allocation implementation. However, it is certainly possible that – under the right conditions – this vulnerability could lead to remote code execution.

Original References and Further Reading

For more information on the utf8asn1str() function and the CVE-2024-6197 vulnerability, refer to the following resources:

- The libcurl source code – particularly the ASN.1 parser module
- The official CVE-2024-6197 description
- Memory management in C (Wikipedia)

Conclusion

In conclusion, the CVE-2024-6197 vulnerability in libcurl's ASN.1 parser is a serious issue that, in specific circumstances, could lead to memory corruption and remote code execution. Developers using the libcurl library should ensure that they are using a secure and up-to-date version of the library, and administrators of affected systems should apply necessary patches and updates. Additionally, security researchers and application developers should take note of this vulnerability when dealing with libcurl and ASN.1 parsing, as it highlights the importance of robust memory management and proper error handling in software design.

Timeline

Published on: 07/24/2024 08:15:03 UTC
Last modified on: 08/26/2024 15:25:59 UTC