A critical security vulnerability, indexed as CVE-2023-4527, has been discovered in the GNU C Library (glibc). The flaw lies in the getaddrinfo function when called with the AF_UNSPEC address family and the system configured in no-aaaa mode via /etc/resolv.conf. This vulnerability can potentially disclose stack contents through the function returned address data and may cause a crash in susceptible systems. To guide you through understanding this vulnerability, this post will provide code snippets, details about the exploit, and references to original sources.

The Vulnerability

The getaddrinfo function is responsible for resolving hostnames into one or more IP addresses when called with an AF_UNSPEC address family. However, when the system is configured in no-aaaa mode, it restricts the function to only resolve IPv4 addresses. The vulnerability arises when an attacker sends a DNS response larger than 2048 bytes over TCP. This causes a buffer overflow, corrupting the stack contents, and may result in unexpected application crashes or even the disclosure of sensitive information residing on the stack.

Code Snippet

Consider the following code snippet, which demonstrates the use of the getaddrinfo function in a vulnerable scenario:

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>

int main() {
    struct addrinfo hints, *res;
    int err;

    memset(&hints, , sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;

    err = getaddrinfo("example.com", NULL, &hints, &res);
    if (err != ) {
        printf("getaddrinfo: %s\n", gai_strerror(err));
        return 1;

    // Further processing of res...


In this example, the getaddrinfo function is called with the AF_UNSPEC address family, making it vulnerable to CVE-2023-4527 if the system is configured in no-aaaa mode via /etc/resolv.conf.

Exploit Details

To exploit this vulnerability, an attacker would need to craft a DNS response larger than 2048 bytes and send it over TCP to a victim system that uses glibc's getaddrinfo function. Once received, the oversized DNS response would trigger a buffer overflow, potentially exposing sensitive information from the stack or causing the application to crash due to memory corruption.


To mitigate this vulnerability, users and administrators should update their glibc and recompile vulnerable applications using the patched glibc version. Furthermore, it is recommended to configure systems not to use the no-aaaa mode or restrict incoming DNS responses to a maximum size of 2048 bytes.


For more details on this vulnerability and the corresponding patch, please refer to the following sources:

1. glibc Project Repository
2. getaddrinfo Function in glibc documentation
3. CVE-2023-4527 - NVD Entry


CVE-2023-4527 is a critical security vulnerability in glibc that impacts systems configured in no-aaaa mode via /etc/resolv.conf when using the getaddrinfo function with the AF_UNSPEC address family. Users and administrators should update their glibc and recompile vulnerable applications as a precautionary measure. By staying vigilant and informed, we can mitigate the risks associated with this memory leak vulnerability.


Published on: 09/18/2023 17:15:55 UTC
Last modified on: 11/07/2023 04:22:41 UTC