The Common Vulnerabilities and Exposures (CVE) program recently identified a critical buffer overflow vulnerability in the widely used c-ares library, which can result in potential security risks, such as denial-of-service (DoS) attacks and remote code execution. This vulnerability has been assigned the identifier CVE-2020-22217, and it affects c-ares versions before 1.16.1, continuing through to 1.17.. In this post, we will delve deeper into this vulnerability, discuss its potential impact, and explore the necessary steps to mitigate the risk associated with this issue.

Details of the Vulnerability

CVE-2020-22217 involves a buffer overflow vulnerability stemming from the ares_parse_soa_reply function within the file ares_parse_soa_reply.c. The issue occurs due to improper handling of responses from the DNS resolver containing Start of Authority (SOA) records. Attackers can exploit this vulnerability by sending a specially crafted DNS response, resulting in a buffer overflow. Consequently, this could permit arbitrary code execution on the target system or cause a denial-of-service attack by crashing the affected application.

The vulnerable code snippet is as follows

  /* Decode the header. */
  memcpy(&header, abuf, HFIXEDSZ);

In this code snippet, we can observe that a fixed-size buffer header is being used to store decoded data from an attacker-controlled buffer abuf. There are no proper bounds checks on the size of the abuf before the memcpy operation is executed. As a result, an attacker can potentially overflow the header buffer, causing memory corruption that could subsequently lead to arbitrary code execution or application crashes.

Original References

- CVE-2020-22217
- c-ares GitHub Repository
- Official Advisory for c-ares

Exploitation Details

To exploit this vulnerability, attackers need to craft a malicious DNS response containing an SOA record with a size exceeding the fixed buffer limit. When this malicious response is received by the vulnerable c-ares library, it causes a buffer overflow, potentially allowing attackers to execute arbitrary code on the victim's machine or cause a denial-of-service attack by crashing the application.

The c-ares project has addressed this vulnerability in the following patch

- c-ares security patch for CVE-2020-22217

To mitigate this vulnerability, users should update their c-ares library to version 1.16.1 or newer. Moreover, developers are encouraged to implement proper bounds checking and input validation when working with potentially untrusted data to avoid buffer overflow issues.


CVE-2020-22217 highlights the importance of input validation and buffer management in any software applications. By understanding the potential risks and vulnerabilities of third-party libraries, developers can take proactive measures to secure their codebase and mitigate any possible exploitation. Following secure coding practices, staying up-to-date with security patches, and keeping an eye on the CVE database will help in building safer and more resilient software systems.


Published on: 08/22/2023 19:16:00 UTC
Last modified on: 09/15/2023 09:15:00 UTC