New Attack Tool Exploits SSL Renegotiation Bug 47
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."
Re: (Score:1)
2ndly, that crap's just plain broken. Look, when I heard MD5 (and later SHA1) MIGHT be vulnerable to some kinds of attacks, I just upgraded to a better hash with no known exploits.
The sooner we adopt IPv6 & DNSSEC the better. Oh, it's expensive? Well, who's fault is it that your companies didn't PLAN TO UPGRADE... EVER!?
Just for the hell of it I wrote an encryption system & protocol for my game's network protocol that's extensible to whatever block length you want, and accepts any cipher -- even "ONE WAY" ciphers (hashes) -- resulting in PSK + PKI reversible encryption and identity services. Right now it's running on SHA256, and I just drop in a SHA512 algorithm's function pointer when I want to upgrade. The protocol auto negotiates down to the "minimum allowed" -- Wait -- What I mean is: THIS SHIT'S NOT HARD, FIX THE DAMN THING YOU CHEAP BASTARDS.
Cry me a river, I've got a bridge to test out.
Oh my bajeebus! You figured out howto use dependency injection and delegates! Get this person a gold star and a green gumball! Now get this to work outside of your walled garden, across multiple Arch's, OS's, and software in a way that equally benefits all, write the rfc and get it promoted into a standard.
Re: (Score:2)
https://github.com/fail2ban/fail2ban [github.com]
NON ISSUE (Score:5, Informative)
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 [nist.gov]
Re: (Score:1)
I recently noticed that myself. Had to re-enable SSL renegotiation via about:config so I could login to various secure websites with my smartcard.
Re: (Score:2)
Speaking of you, doesn't Woot! invite this kind of attack at least once a month?
SSL renegotiation not required (Score:2)
Re: (Score:2)
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 (Score:3)
Is it a Bug? (Score:3, Interesting)
Sounds more like a protocol flaw than a bug.
Apache Server Settings (Score:4, Informative)
Re: (Score:1)
how can a real DoS attacks that affects a significant percentage of the web servers be considered overhyped?
Here is how:
#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 [apache.org] 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.
Or since you obviously didn't get it the first time- this is old news, old exploit, old old old. The only news here is that somebody released a new tool to do it for you. Or in other words, the haxxors are using slashdot as a marketing platform again.
Who needs tools when we have wget? (Score:2)
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.
Analysis of this from TLS WG Chair (Score:2)
Good analysis of this at
http://www.educatedguesswork.org/2011/10/ssltls_and_computational_dos.html [educatedguesswork.org]
As far as I can tell, Rescorla is trying to polity say this attack is crap. Shocking, yet another low grade hack trying to up publicity.
Re: (Score:2)
It's a real attack and a real DoS vector. SSL/TLS is definitely weak in this regard.
But it's not new and it doesn't have much to do with renegotiation.
https not the only thing to test (Score:2)
pop3s, imaps, smtps, etc. anything that uses ssl should be tested and is probably vuln (quick dovecot & sendmail tests were). I'd really like to see the "private" code that works w/o renegotiation in order to test against https.
Re: (Score:2)
how come there's no flood protection?
per ip it would cause some big natted networks(looking at you cellphone operators) to get blacklisted I suppose but still..
It worked for the wrong reason. (Score:3)
This tool excels in finding bugs and session cache synchronization deadlocks in the latest daily snapshots of openssl.. I found two within 2 minutes..
Re: (Score:1)
..Researchers, Hackers, Authors. Now who? (Score:2)
..Researchers, Hackers, Authors. Sounds like lots of people are involved, or are they all hackers (since they simply released it in the wild, i wouldn't say researchers)
"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."
iptables (Score:4, Informative)
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
Re: (Score:2)
hey, you can always post the same script in IPFW/PF so we can compare...
just in case you didnt read. that is (part of) a script, full of long variable names... yes, their names could be better, the rule_j14 is weird name, the multi-line makes it harder to read... bug again, this is clearly just a small part of s bigger script and the user ls671 didnt wanted to clean it up... simply because the idea is there, adapt that for your own use.
Re: (Score:2)
for redirport in 25 587 995 21 113 22 563 119
Not allowing any 443 (HTTPS) traffic should do the trick :P IMHO I would rethink allowing ftp and ssh from the outside world.
hmmmm (Score:2)
Don't SSL renegotiations have, or follow, packets with the PSH flag set? I'll have to check it out; but, I seem to remember it looks like one or the other. If someone knows off the top of their head it would be helpful.
Re: (Score:2)
It looks like PSH is set ON the renegotiation packet.
08:54:25.852659 IP localhost.localdomain.51515 > localhost.localdomain.6060: Flags [P.], seq 1:62, ack 1, win 513, options [nop,nop,TS val 19313608 ecr 19313608], length 61
08:54:25.852793 IP localhost.localdomain.51516 > localhost.localdomain.6060: Flags [P.], seq 1:62, ack 1, win 513, options [nop,nop,TS val 19313609 ecr 19313609], length 61
Releasing this so called tool (Score:1)
I'm the guy who found CVE-2009-3555 renego bug (Score:2)
This is not a bug. We fixed renegotiation with the RFC 5746 RI extension! That said, SSL has long been known to impose more work on the server than on the client and renegotiations are no different than initial handshakes in this respect.
Servers that accept client-initiated renegotiation make things slightly more efficient for the DoS attacker, it saves him maybe three packets. More significantly, it may bypass mitigations that are only looking for TCP SYN packets. But the attacker's mileage will vary.
E