CVE-2015-0235 – How to secure against Glibc Ghost Vulnerability

CVE-2015-0235 Ghost (glibc gethostbyname buffer overflow) Vulnerability is serious cause for all Linux servers. This vulnerability leveraged to execute remote and  code execution on the victim Linux server. The vulnerability found By Qualys Researcher and patched in GNU.

What is the cause ?

The bug is in __nss_hostname_digits_dots() function of function of the GNU C Library (glibc), and location of the path is file for  non-reentrant version is nss/getXXbyYY.c , which is used by the gethostbyname().  The vulnerability can be exploited both via locally and remotely.  In order to trigger this vulnerability attacker needs to be able to feed specially crafted ‘host name’ to the service. And service needs to process it without validating it first.

Following are the potentially exploitable services

1. procmail
2. Exim
3. pppd
4. clockdiff

You can find the list of services which are rely on the GNU C libraries by executing following command
lsof | grep libc | awk ‘{print $1}’ | sort | uni

Fix for Centos/RHEL/Fedora 5,6,7

yum update glibc
sudo restart

Fix for Ubuntu

sudo apt-get update
sudo apt-get dist-upgrade
sudo restart

For Quick test , you can run this code

/* ghosttest.c:  GHOST vulnerability tester *//* Credit: http://www.openwall.com/lists/oss-security/2015/01/27/9 */#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
 
#define CANARY "in_the_coal_mine"
 
struct {
  char buffer[1024];
  char canary[sizeof(CANARY)];
} temp = { "buffer", CANARY };
 
int main(void) {
  struct hostent resbuf;
  struct hostent *result;
  int herrno;
  int retval;
 
  /*** strlen (name) = size_needed - sizeof (*host_addr) - sizeof (*h_addr_ptrs) - 1; ***/  size_t len = sizeof(temp.buffer) - 16*sizeof(unsigned char) - 2*sizeof(char *) - 1;
  char name[sizeof(temp.buffer)];
  memset(name, '0', len);
  name[len] = '\0';
 
  retval = gethostbyname_r(name, &resbuf, temp.buffer, sizeof(temp.buffer), &result, &herrno);
 
  if (strcmp(temp.canary, CANARY) != 0) {
    puts("vulnerable");
    exit(EXIT_SUCCESS);
  }
  if (retval == ERANGE) {
    puts("not vulnerable");
    exit(EXIT_SUCCESS);
  }
  puts("should not happen");
  exit(EXIT_FAILURE);
}