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DDOS Attacksand Mitigation Methods
Özkan Erdoğ[email protected]
Ms.C, CISA, CEH, ISO 27001 LA
BTPSec Corp [email protected]
Office:+90 216 4647475 +44 203 6084760
Address:Turaboğlu Sk. Hamdiye Yazgan İş Merkezi, Kozyatağı Kadıköy İSTANBUL
What is DOS & DDOS?
D = Distributed DOS : focused on vulnerabilities, using single source DDOS : overflow focused, using multiple sources Target of attacks is to eliminate availability of the resource
Is it possible to mitigate Ddos attacks?Our experience shows that its quite possible to mitigate ddos attacks. However, there are caveats such
that: Most ddos attacks come big in volume where it saturates your bandwidth . Attack volume > Target
network bandwidth (mbps).These attacks can be handled by obtaining service from global anti ddos providers: e.g. Cloudflare, Incapsula, Akamai etc.
Other kinds of attacks are usually ineffective if we configure our network with correct measures.
Ddos Survey Results
61% loss of access to information
38% business stop
33% loss of job opportunities
29% reputation loss
26% insurance premium increases
65% Received security consultancy
49% More investments on IT
46% Started legal processes
43% Informed customers
36% Applied legal ways
26% Informed the media
● Spamhaus● Chinese domain authority (.cn)● Pohjola -Finland bank ● Nasdaq● Bitcoin● Bank of America
BOTNETs
Controlled by Botnet herders Commanded via : Mirc, http(s), Tor (popular now) Injection methods: Wordpress, Joomla etc. old Windows systems are
easiest targets.
Botnet members are targeted to be amongst data center systems.
DDOS events
1. Spamhaus (DNS Amplification) 300gbps.a. 11 Feb 2015: New NTP attack: 400gbps
2. Brobot (American Financial companies)3. Chinese attacks4. Russia: DDOS gangs5. Syn reflection attacks are gaining a rise.
DDOS Mitigation Methods (General)
ACL BGP Routing (Cloud service) Blackhole Mitigation devices (Inline, Offline)
Basic DDOS Attacks
Signature based attacks (Teardrop, Land, Smurf, Nuke,Fraggle vb) Volumetric attacks (legal and illegal attacks) Reflection (dns, syn) Application based attacks: e.g. Slow attacks Connection attacks
Protocols used in DDOS
TCP/IP Tcp,udp, icmp,
Other (GRE, ESP etc) IPv4 IPv6 Application layer
Http, dns, VOIP etc.
IP Spoofing (&How to detect it)
uRPF- Unicast reverse path forwarding. Source IP of packet is compared to the FIB table in router and
dropped if routes are not the same. Authentication First packet drop, and let following packets go.
Attack Tools
Hping, nping, mz, isic Slowloris, httpflooder, Torshammer, jmeter, ab, httpDOS, R-U-D-Y,
pyloris etc. Scripts (socket programming: Python, Perl etc)
Volumetric Attacks
Band filling attacks Network attacks (syn, syn-ack, ack, udp flood etc) Application Attacks (http, https, dns, voip etc) Botnet, HOIC, LOIC
Application Layer DDOS
Slow attack (Apache)- slowloris, pyloris etc Slow Read- tcp window size RUDY- HTTP post XML dos SIP invite- multiple udp calls to overwhelm server..
How to mitigate DDOS attacks?
WL/BL (ALL protocols) ACL (All protocols) Fingerprint (udp, dns) Authentication (tcp, http, dns) Session management (dns, tcp) Statistical Methods Rate Limit
Syn Flood and Prevention
Attacker
ServerSyn
Syn
SynSyn
Syn-Ack
Syn-AckSyn-Ack
• Most popular ddos attack is syn flood.• Protection method: Authentication and WL. (Whitelisting) (Syn
cookie vs. syn proxy)• Syn reflection factor• Syn flood from real IP addresses: TCP ratio mechanism
Syn-Ack Flood and Mitigation
Attacker
ServerSyn-AckSyn-Ack
Syn-AckSyn-Ack
• Protection: Check session table if syn-ack’s are real.
Ack Flood ve Mitigation
Attacker
ServerAckAck
AckAck
• Protection: Check session table if ack’s are real.
FIN/RST Flood and Mitigation
Attacker
ServerFin/RstFin/Rst
Fin/RstFin/Rst
• Protection: Check session table if packets are real.
Udp Flood and Mitigation
Attacker
ServerUdpUdp
UdpUdp
• Udp is the most effective for ddos • Protect method: Payload and Header.
(Fingerprint)• Dest.port, source port, ttl, source/dest IP
also checked• ACL• Traffic limiting
Icmp Flood and Mitigation
Attacker
ServerIcmpIcmp
IcmpIcmp
• Protect method: Payload and Header. (Fingerprint)
• Session check (query, response)• Rate limit• ACL
TCP Connection Flood & Mitigation Low rate attack (Protection: Number of connections are analyzed- Bot detection methods
are used) TCP Null connection attack (No packets after handshake) Also check for rates of:
New connections Total connections per
second
Http Ddos Detection & Mitigation Methods Authentication (Http redirection) SSL Ddos (Crypto handshake messages increase abnormally) Captcha usage Fingerprint
DNS Query/Response Attacks
SP DNS
1. What is the IP for abc.google.com?
2. What is the IP for abc.google.com?
Attacker
3. IP= XXX.XXX.XXX =news.google.com
DNS Reply Flood
Attacker
DNS Cache Poisoning
SP DNS
1. What is the IP for abc.google.com?
2. What is the IP for abc.google.com?
Attacker
3. abc.google.com= x.x.x.x
DNS Reply
Attacker
• Domain info on Cache DNS servers are attempted to be changed with the fake one.
• Attacker should guess the query id correctly. (which is so easy if query id’s are not random)
DNS Reply
DNS Reflection
Open DNS resolvers
1. What is the IP for abc.google.com?
2. What is the IP for abc.google.com?
Attacker
DNS Reply
• Attacker uses victim’s IP address as his source, and sends a dns query to all known dns servers.
• Thousands of resolvers return the answer to the victim and victim is Ddos’ed
DNS Reply
DNS authority
Victim
DNS Attacks
Conclusion:
DNS attacks are very dangerous and can be performed with the least effort and cost .
Ddos attacks are on the rise every year and quite possible to be so in the future.
Udp and Dns based ddos attacks are the most effective protocols for ddos.
Methods To Protect Against DNS Ddos Attacks Session control (Two way traffic) DNS proxy, caching DNS-Tcp Authentication First packet drop Domain name limiting Traffic limiting
An Effective Mitigation Technique: Fingerprinting Packet header and payload is analyzed to determine a fingerprint of
attack.
NTP Amplification ( Attack multiplier 300x)
Can also use snmp for upto 600x , however snmp seldom allows nonauthenticated clients
11 February 2015: New NTP attack: 400gbps
Ddos Summary
Extremely easy to attack ( Many free and user friendly tools) Impossible to be detected (If correctly hides) Big effects on the victim Attack types and methods are broad. Every application or service has its own ddos vulnerabilities ...Spoofing is possible and mostly costless ...AGAIN.. attack tools are free