A flaw has been discovered in GNU C Library (glibc), a widely-used library that provides low-level functionality for C programs running on Linux systems. The vulnerability, identified as CVE-2023-4806, can lead to application crashes under certain conditions. This issue is exceptionally rare, but it's essential to understand the nature of the vulnerability, its potential impact, and what can be done to mitigate it.

Vulnerability Details

The CVE-2023-4806 vulnerability pertains to the getaddrinfo function in glibc. In certain cases, when calling this function, freed memory may be accessed, resulting in an application crash. This issue is considered extremely rare for two main reasons:

1. The problem arises when an NSS (Name Service Switch) module implements only two specific hooks, namely _nss_*_gethostbyname2_r and _nss_*_getcanonname_r, without implementing the _nss_*_gethostbyname3_r hook.
2. The resolved name should return a large number of IP addresses (both IPv6 and IPv4), and the call to the getaddrinfo function must have the AF_INET6 address family with AI_CANONNAME, AI_ALL, and AI_V4MAPPED as flags.

Here's an example code snippet demonstrating the issue

#include <netdb.h>
#include <stdio.h>

int main() {
  struct addrinfo hints = {};
  struct addrinfo *result;
  int error;

  hints.ai_family = AF_INET6;
  hints.ai_flags = AI_CANONNAME | AI_ALL | AI_V4MAPPED;

  error = getaddrinfo("<hostname>", NULL, &hints, &result);
  if (error) {
    fprintf(stderr, "Error: %s\n", gai_strerror(error));
    return 1;
  }

// Do something with the 'result' data structure
// If the bug is triggered, the application may crash here

  freeaddrinfo(result);
  return ;
}

As mentioned earlier, triggering the vulnerability requires a very particular set of circumstances, making it a low-risk issue. However, when faced with these conditions, a crash can occur, affecting system stability.

More information on this vulnerability can be found at the following sources

1. glibc GitHub Repository – Issue Discussion
2. CVE-2023-4806 – National Vulnerability Database Entry

Exploit and Mitigation Details

At the time of writing, no known exploits for CVE-2023-4806 have been publicly released. The nature of the vulnerability makes the development of a working exploit challenging, considering the rare conditions necessary to trigger the flaw. However, it's crucial to stay informed about potential exploits by monitoring reputable security sources and applying any patches or workarounds provided by glibc maintainers or distribution vendors.

Since this vulnerability affects a component of the GNU C Library, the best way to mitigate it would be for the library developers to fix the issue. Administrators and users can then update their systems to use the updated version of glibc, ensuring they are protected against this flaw. Additionally, closely examining the configuration of the NSS modules on a system can help minimize the risk of running into the problem.

Conclusion

CVE-2023-4806 represents an extremely rare vulnerability in glibc that, under specific circumstances, can cause application crashes. While the potential impact of this vulnerability is limited, it serves as a reminder of the importance of staying informed about security developments and regularly updating software components. By applying patches provided by glibc maintainers or distribution vendors and carefully managing NSS module configurations, system administrators can help mitigate the risks posed by this flaw.

Timeline

Published on: 09/18/2023 17:15:55 UTC
Last modified on: 11/07/2023 04:22:59 UTC