A new vulnerability has been discovered and assigned the identifier CVE-2023-0216. This vulnerability leads to an invalid pointer dereference on read when an application attempts to load malformed PKCS7 data using the d2i_PKCS7(), d2i_PKCS7_bio(), or d2i_PKCS7_fp() functions. Although OpenSSL's TLS implementation does not call these functions, third-party applications may use them with untrusted data, potentially resulting in a denial of service attack if exploited. This blog post will deep-dive into the details of this vulnerability, including code snippets, links to original references, and exploitation techniques.

Here's a code snippet that demonstrates the use of the vulnerable d2i_PKCS7() function

#include <openssl/pkcs7.h>

int main()
{
    unsigned char pkcs7_data[] = { /* Malformed PKCS7 data */ };
    const unsigned char *p = pkcs7_data;
    PKCS7 *pkcs7 = d2i_PKCS7(NULL, &p, sizeof(pkcs7_data));

    if(!pkcs7) {
        printf("Failed to load PKCS7 data\n");
        ERR_print_errors_fp(stderr);
        exit(EXIT_FAILURE);
    }

    // ... Use the PKCS7 object for further processing

    PKCS7_free(pkcs7);
    return EXIT_SUCCESS;
}

In this example, the d2i_PKCS7() function is called to load the malformed PKCS7 data into a PKCS7 object. Since the data is malformed, an invalid pointer dereference on read occurs, which results in an application crash.

1. CVE-2023-0216 Details
2. OpenSSL Security Advisory
3. National Vulnerability Database

Exploit Details

To successfully exploit CVE-2023-0216, an attacker must be able to provide a maliciously crafted PKCS7 file to a vulnerable application. The attacker could potentially insert this malformed data into a file or network stream that the target application processes with the vulnerable functions (d2i_PKCS7(), d2i_PKCS7_bio(), or d2i_PKCS7_fp()).

Upon processing the malicious data, the application will encounter the invalid pointer dereference, leading to a crash and potential denial of service. While exploiting this vulnerability does not necessarily grant an attacker control over the target system, it can disrupt normal operations and cause additional consequences for the affected service or software.

Mitigation and Conclusion

The best way to mitigate this vulnerability is to ensure that the functions d2i_PKCS7(), d2i_PKCS7_bio(), and d2i_PKCS7_fp() are never called on untrusted data without first applying proper input validation and sanitization techniques.

To sum up, CVE-2023-0216 is an invalid pointer dereference vulnerability in the PKCS7 data loading functions of OpenSSL which can potentially lead to denial of service attacks when exploited. Developers should, therefore, ensure that they are using these functions with proper validation when processing untrusted data to address potential risks.

Timeline

Published on: 02/08/2023 20:15:00 UTC
Last modified on: 02/24/2023 15:15:00 UTC