check_freak.sh - A simple nagios-compatible check for the FREAK vulnerability (CVE 2015-0204)

check_freak.sh

#!/usr/bin/env bash

# check_freak.sh
# (c) 2015 Martin Seener

# Simple script which checks SSL/TLS services for the FREAK vulnerability (CVE 2015-0204)
# It will output if the checked host is vulnerable and returns the right exit code
# so it can also be used as a nagios check!

PROGNAME=$(basename $0)
VERSION="v0.2"
AUTHOR="2015, Martin Seener (martin@seener.de)"

# Set the timeout how long openssl can try to connect to the service
TIMEOUT=10

print_help() {
  echo ""
  echo "$PROGNAME is a small shell script which checks remote SSL/TLS services for the FREAK vulnerability (CVE 2015-0204)"
  echo "It will return if the service is vulnerable or not and exit with 0 (OK) or 2 (CRIT) so it can be used as"
  echo "a nagios check too"
  echo ""
  echo "Usage: ./$PROGNAME <IP or Hostname> <port>"
  echo "Example: ./$PROGNAME www.google.com 443"
  echo ""
}

initialize() {
  if [ -z "$1" ]; then
    echo "The Hostname/IP Argument is missing!"
    echo ""
    print_help
    exit 3
  fi
  if [[ ! $2 =~ ^[0-9]+$ ]] || [ $2 -eq 0 ] || [ $2 -gt 65535 ] ; then
    echo "The Port argument must be a positive integer value starting at 1 up to 65535"
    echo ""
    print_help
    exit 3
  fi
  OPENSSL=$(which openssl)
  if [ "$OPENSSL" == "" ]; then
    echo "Cannot find openssl! Aborting!"
    echo ""
    print_help
    exit 3
  fi
}

check_freak() {
  # Get the information (we use the strange sleep/kill method here because timeout doesn't work on OSX by default!)
  CHK=$( $OPENSSL s_client -connect $1:$2 -cipher EXPORT < /dev/null 2>/dev/null & sleep $TIMEOUT; kill $! 2>/dev/null )
  if [ "$CHK" == "" ]; then
    echo "UNKNOWN - Timeout connecting to $1 on port $2"
    exit 3
  fi
  # Check if there is an export cipher
  echo $CHK | grep "Cipher is EXP" > /dev/null
}

case "$1" in
  --help|-h)
    print_help
    exit 3;;
  *)
    ;;
esac

# Initialize
initialize $1 $2

# Do the check
check_freak $1 $2

# Return the result
if [ $? -eq 1 ]; then
  echo "OK - $1 on port $2 is PROBABLY NOT vulnerable to FREAK (CVE 2015-0204)"
  exit 0
else
  echo "CRITICAL - $1 on port $2 IS PROBABLY VULNERABLE to FREAK (CVE 2015-0204)"
  exit 2
fi

Thanks to @scottwilkerson for his updates in his fork. I've incorporated them and made the timeout for openssl compatible to OSX as well (the timeout command doesn't exist on OSX by default!)

I shortened it for you:

chkit() { grep ' EXP-' &>/dev/null <(timeout 2 openssl s_client -connect $1:443 -cipher EXPORT 2>/dev/null) && echo VULNERABLE || echo SECURE ;}

e.g.

$ chkit www.google.com
SECURE

$ chkit mail.excite.com
VULNERABLE

-jb

Hey guys, many thanks for putting this out in the public domain.

I was looking over your PoC and seems it would have a high false positive potential in a scenerio where the end point has been patched but still chooses to use export ciphers.

I'm only mentioning this because the verbiage of ("VULNERABLE") seems a bit strong given what you're actually testing. I think it's fair to assume that a target that doesn't use export ciphers is not vulnerable to this, but the presence of export ciphers isn't a smoking gun to imply vulnerability. IMO, it has potential to be vulnerable and that's about all we can say without going further down the path of exploitation.

With that said, I'm open to contrary opinions to my own just to ensure there isn't something that I've overlooked in your PoC or understand about the vulnerability.