New Attack Tool Exploits SSL Renegotiation Bug

Trailrunner7 writes "A group of researchers has released a tool that they say implements a denial-of-service attack against SSL servers by triggering a huge number of SSL renegotiations, eventually consuming all of the server's resources and making it unavailable. The tool exploits a widely known issue with the way that SSL connections work. The attack tool, released by a group called The Hacker's Choice, is meant to exploit the fact that it takes a lot of server resources to handle SSL handshakes at the beginning of a session, and that if a client or series of clients sends enough session requests to a given server, the server will at some point fail. The condition can be worsened when SSL renegotiation is enabled on a server. SSL renegotiation is used in a number of scenarios, but most commonly when there is a need for a client-side certificate. The authors of the tool say that the attack will work on servers without SSL renegotiation enabled, but with some modifications."

Comments

NON ISSUE

[Anonymous Coward]

This is like the 3rd or 4th SSL renegotation bug. The last one had only one fix: disable SSL renegotiation altogether. Firefox helped speed it along, but marking ssl servers that allowed renegotiation as insecure. And openssl released an updated version to drop support for it.

So pretty much every SSL server has renegotiation disabled.

IIRC it was this bug: CVE-2009-3555

SSL renegotiation not required

[CanEHdian]

From what I have read, the renegotiation part only made the tool more effective, such that under optimal conditions a single laptop on ADSL was enough to bring down a server on a 30 gigabit connection. An SSL handshake still requires server resources, so perhaps we'll see this used in DDoS tools like LOIC.

Re:SSL renegotiation not required

[d4fseeker]

LOIC DDOS' mostly relies on large bandwiths to disable their target - regardless of the server's processing capacity.
This issue can be tackled with 3 lines of iptables (ratelimit connections/time and concurrent connections), at least for low capacities.
Most clients are perfectly capable of HTTP keep-alive and thus we can set the limit significantly lower on HTTPS than on HTTP; all we need is a reverse proxy between Apache and the clients or apache mpm_event.

Facebook API now requires SSL/TLS

[crazybit]

Considering Facebook API now requires SSL/TLS for Facebook Apps, many servers had to turn on HTTPS just for this. It's just a matter of time until we see this widely exploited.

Is it a Bug?

[allo]

Sounds more like a protocol flaw than a bug.

Apache Server Settings

[triemer]

#1 - this has been a topic of conversation for a while #2 - per documentation at apache (Yes, I dare say a majority of web servers are running apache) There is a flag that can turn renegotiation on/off http://httpd.apache.org/docs/2.0/mod/mod_ssl.html Available in httpd 2.0.64 and later, if using OpenSSL 0.9.8m or later The default setting is: SSLInsecureRenegotiation off #3 - which leads to the conclusion that this is overhyped.

Who needs tools when we have wget?

[Mereel]

for i in {1..10}; do (while true; do wget https://poor.server; done)& done

A dedicated tool may be even more efficient, but bash and wget do the trick too.

It worked for the wrong reason.

[WaffleMonster]

This tool excels in finding bugs and session cache synchronization deadlocks in the latest daily snapshots of openssl.. I found two within 2 minutes..

iptables

[ls671]

INTIF2=vmnet1
PORTFWIP2=192.168.4.38

$IPTABLES -A rule_j14 -m limit --limit 120/minute --limit-burst 50 -j ACCEPT
$IPTABLES -A rule_j14 -m limit --limit 1/minute -j LOG --log-prefix "wharf"
$IPTABLES -A rule_j14 -j DROP

let i=0
while [ $i -lt $EXTIF_LIST_SIZE ]
do
for redirport in 25 587 995 21 113 22 563 119
do

$IPTABLES -A INPUT -i ${EXTIF_LIST[i]} -p tcp --dport ${redirport} \
-m state --state NEW -m limit --limit 1/minute \
-j LOG --log-prefix "wharf wharf"

$IPTABLES -A INPUT -i ${EXTIF_LIST[i]} -p tcp --dport ${redirport} \
-m state --state NEW -j DROP
$IPTABLES -A FORWARD -i ${EXTIF_LIST[i]} -o $INTIF2 -d ${MAIL_FW_IP[i]} -p tcp \
--dport $redirport -m state --state NEW -j rule_j14

$IPTABLES -A FORWARD -i ${EXTIF_LIST[i]} -o $INTIF2 -d ${MAIL_FW_IP[i]} -p tcp \
--dport $redirport -m state --state ESTABLISHED,RELATED -j ACCEPT

$IPTABLES -A PREROUTING -t nat -p tcp -d ${EXTIP_LIST[i]} --dport $redirport \
-m state --state NEW -m hashlimit --hashlimit 60/hour --hashlimit-burst 15 \
--hashlimit-htable-expire 3600000 --hashlimit-mode srcip,dstport \
--hashlimit-name j14-${redirport} \
-j DNAT --to ${MAIL_FW_IP[i]}:$redirport

done
let i=$i+1
done