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Comprobar si somos vulnerables a Ghost CVE-2015-0235

Mediante un .c hecho por la Universidad de Chicago podemos comprobar si somos vulnerables a Ghost (CVE-2015-0235): Una vulnerabilidad de buffer overflow de glibc en las funciones gethostbyname() y gethostbyname2()

Pasteando el siguiente script en la shell podremos verificar si somos o no vulnerables:

GHOSTTEMP=$(mktemp /tmp/ghost.XXXXXXXXXXXXXX)
GHOSTEXEC=$(mktemp /tmp/ghost.XXXXXXXXXXXXXX)
cat <"EOF" > $GHOSTTEMP
#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] = '';

  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);
}
EOF
gcc -x c $GHOSTTEMP -o $GHOSTEXEC
$GHOSTEXEC
rm -f $GHOSTTEMP $GHOSTEXEC

En caso que seamos vulnerables tendremos:

(...)
# gcc -x c $GHOSTTEMP -o $GHOSTEXEC
# $GHOSTEXEC
vulnerable
# rm -f $GHOSTTEMP $GHOSTEXEC

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Comprobar si somos vulnerables a Ghost CVE-2015-0235

One response

  1. Youu actually ake it seem so easy with your presentation buut I find this topic to be actually something that I think I would never understand.
    It seems too complicated and extremely broad for me. I’m looking forward for your
    next post, I will try to get the hang of it!

    February 27, 2015 at 05:23