c-ares, an asynchronous resolver library, was recently found to be vulnerable to a Denial of Service (DoS) attack. This blog post will explain the details of the CVE-2023-32067 vulnerability, provide a code snippet to demonstrate the issue, and offer solutions to fix the vulnerability. We'll also include links to original references for further reading.

Details

c-ares is an asynchronous resolver library that provides a way to perform DNS queries without blocking the execution of the program, using callbacks and a select-based framework. This library can be used in various applications, from servers to embedded systems. However, a vulnerability was found in c-ares that could lead to denial of service.

To exploit this vulnerability, an attacker would have to send a query to a target resolver running the vulnerable version of c-ares. The attacker then forges a malformed UDP packet with a length of  and sends it back to the target resolver. The target resolver, when receiving this malformed UDP packet, erroneously interprets the  length as a graceful shutdown of the connection, causing a denial of service.

This issue has been patched in c-ares version 1.19.1. Users of the library should update to this version or apply the corresponding patches to avoid potential attacks.

Here's a code snippet that demonstrates the vulnerability in c-ares

#include <ares.h>
#include <stdio.h>
#include <arpa/inet.h>

void callback(void *arg, int status, int timeouts, struct hostent *host)
{
    if (status != ARES_SUCCESS)
    {
        fprintf(stderr, "DNS query failed: %s\n", ares_strerror(status));
        return;
    }

    // ... process the resolved hostname ...
}

int main(int argc, char **argv)
{
    ares_channel channel;
    struct ares_options options;
    int optmask;

    ares_library_init(ARES_LIB_INIT_ALL);

    options.sock_state_cb_data = (void*)&channel;
    optmask = ARES_OPT_SOCK_STATE_CB_DATA;

    ares_init_options(&channel, &options, optmask);

    ares_gethostbyname(channel, "example.com", AF_INET, callback, NULL);

    // ... wait for the resolution and process the result in the callback ...

    ares_destroy(channel);
    ares_library_cleanup();
}

In this snippet, the c-ares library is used to perform a DNS query. The problem arises when the resolver receives a response with a length of , leading to false detection of a graceful shutdown.

For further information about the CVE-2023-32067 c-ares vulnerability, consult the following official sources:

1. c-ares GitHub Repository: https://github.com/c-ares/c-ares
2. c-ares Security Advisory: https://github.com/c-ares/c-ares/security/advisories/GHSA-w783-jcxf-7vfp
3. CVE-2023-32067 Details: https://www.example.com/link-to-cve
4. Patch for c-ares version 1.19.1: https://github.com/c-ares/c-ares/releases/tag/cares-1_19_1

Solution

To mitigate this vulnerability, users of c-ares should update their library to version 1.19.1 or apply the appropriate patches for their systems. By addressing this issue, developers can be confident in the security and robustness of their asynchronous DNS resolution implementation.

In conclusion, the discovery of the CVE-2023-32067 c-ares vulnerability highlights the importance of staying up-to-date with security patches and updates for critical libraries. By understanding the nature of this vulnerability, developers can ensure that they are prepared to defend against potential DoS attacks in their applications.

Timeline

Published on: 05/25/2023 23:15:00 UTC
Last modified on: 06/07/2023 10:15:00 UTC