The document discusses NTP amplification attacks and their implications for various industries, detailing the nature of DDoS attacks, including definitions and classifications. It highlights the vulnerabilities of NTP protocols, particularly the monlist command, which can be exploited to generate excessive traffic towards targeted networks. The document also outlines countermeasures, such as upgrading NTP versions and implementing response rate limitations to mitigate these types of attacks.

1. 0Document Title
NTP in Amplification Inferno
Sriram Krishnan

2. 1Document Title
To Introduce Myself...
 Sriram Krishnan
 Senior Manager, Security Solutions, Group Information Security - Scope International
Pvt. Ltd. (A wholly owned subsidiary of Standard Chartered Bank)
 Over 9 years of experience in Information Security

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Agenda
 Why NTP Amplification?
 Demystifying DDoS
 Time to Deep Dive
 NTP Amplification Attack – Demo
 Challenges & Countermeasures

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Why NTP Amplification?

5. 4Document Title
A Background

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Why NTP?
 Why NTP is targeted
 Ease of attack:
 Small request may lead to relatively large response
 Evade Detection:
 Spoofing of IP Address due to lack of handshake process– as
it is a UDP based protocol
 Availability:
 Essential service with large clusters of public timeservers
available in internet
 Traffic Volume:
 Potential to generate from 200 to 400Gbps of traffic that will
shutdown a network
Targeted Industries
 Internet Service
Providers,
 Banks and
Financial Services,
 Managed Services
(Including SaaS),
 Critical
Infrastructure of
countries
 e-Commerce

7. 6Document Title
Demystifying DDoS

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Understanding DDoS Terminology
 Master / Handler
Compromised system in the interest used by the attacker to launch attacks.
 Slave / Agent:
System that responds to the instructions of Master which are controlled by the attacker. Slave
serves as the amplifiers for DDos attacks.
 Daemon:
Process running the Slave, executing the commands for amplification.
 Reflector
Systems that respond to instructions of Master, without the awareness of participating in DRDoS
attack.
 Victim
Target host or network for the DDoS attack.

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DDoS Categorized Based on Attack Method
Conventional DDoS Attack:
 Attacker takes control of master system to send instructions to slaves running the affected
daemon.
 The slaves will execute the command and amplify the traffic to finally send it to victims.
Compromised Systems
Fig 1: Distributed Denial of Service (DDOS) Attack

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DDoS Categorized Based on Attack Method
Distributed Reflective Denial of Service Attack
 Attacker takes control of the master system and sends instruction to reflector running the
vulnerable daemon.
 Reflectors executes the command and amplifies the traffic to finally send it to victims.
 Host of both categories (Master and Slave) are compromised in DDoS, but in DRDoS attack the
reflector is not compromised.
Compromised Systems
Fig 2: Distributed Reflective Denial of Service (DRDOS) Attack

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DDoS Categorized Based on Impact
 Volume / Bandwidth Based Attacks
 Chokes victim’s network bandwidth
 Measured in bits per second (Bps)
 Example: UDP Flood, ICMP Flood
 Protocol Based Attacks
 Exhaust the system / network device resources and shutdown the service or systems
 Measured as packets per second
 Example: SYN Flood, Ping of Death, Smurf DDoS
 Application Layer Based Attacks
 Shutdown application layer resources / services
 Example: Slowloris, HTTP Flood.

12. 11Document Title
Time to Deep Dive

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Vulnerability Details
 NTP allows administrators to monitor service via ntpd daemon – by executing remote commands
 Affected command is monlist
 monlist command operates in mode 7 – private use (which allows remote administration).
 Purpose of this command is to obtain details about NTP Associations (up to 600) from NTP server
 NTP Associations are formed when two peers exchange messages, and this transaction is
maintained in the Most Recently Used (MRU) list.
 NTP Associations details are stored in ntp.conf file. Example, in unix-based OS this file is stored in
</etc/ntp.conf>
 Attacker sends a request (get_monlist ) to public NTP Server (in internet) with spoofed IP of the
victim
 Response to this request generates enormous traffic towards the victim’s network

14. 13Document Title
Monlist Command – Understanding the Details

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Examining the Source Code
Let’s examine the source code that defines the structure and executes the monlist command
 ntp_request.c - respond to information requests
 ntp_monitor.c - monitor who is using the ntpd server
ntp_request.c
 mon_getlist_1 function obtains MRU list from the NTP server.
 Arrow indicates structure of mon_data that defines the maximum number of NTP associations.
 The keyword “extern” is used as this variable has already been defined in ntp_monitor.c.

16. 15Document Title
Examining the Source Code (Contd..)
ntp_monitor.c
 First arrow - defines the number of structure to be allocated - 600
 Second arrow - declares and defines the mon_data that updates the statistics of the monitoring data.

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NTP Amplification Attack
Spoofed IP Address of Victim
monlist
NTP Associations
MRU List

18. 17Document Title
Demo

19. 18Document Title
Challenges & Countermeasures

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Challenges in Defence
 Arresting Help
 DDoS attack floods victim’s network / systems with malicious packets.
 Traffic flow increases rapidly within a quick span of time and without any prior warning or alert.
 This prevents systems to send SoS and are arrested from the attack.
 Filtering of Traffic
 Any attempts made to filter the traffic, hampers service rendered
 All legitimate traffic may be filtered / rejected thus denying service
 Evade Detection
 Generally attackers spoof the IP address of the attack packets.
 Attack triggered from distributed compromised systems
 Heterogeneous Environment:
 Systems with multiple software and diverse architecture are deployed.

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Countermeasures
So what is required?
Robust & effective defensive mechanism
How?
Enhancing the protocol design

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Countermeasures – NTP Amplification Attacks
 Upgrade the ntpd version to 4.2.7
 If the ntpd version cannot be updated, add the “noquery” directive to the “restrict default”
line in the ntp.conf file.

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Countermeasures - DDoS Attacks
 Response Rate Limitation (RRL)
 Limits number of packets issued to a target at a given time interval
 Excess data over the limit is truncated
 Works best when the attack source is limited
 Already implemented in DNS protocol
 Protocol Harding
 Session handling mechanism - requests to be processed only post session initiation
 For example, DTLS (RFC 4347), a UDP-variant of TLS, implements a stateless cookie exchange
mechanism in order to avoid DDoS attacks.
 Response Size Limitation
 Protocol to be designed to:
 Limit the output (packet size) for every request, and
 Demand session initiation before releasing the rest of the output

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To Sum Up!
 UDP based network services - easy target for attackers
 Other UDP based services such as SNMP, SSDP, NetBIOS targeted
 Pressing need to harden such protocol design
 Need for investments in preventive defence mechanism pertinent

25. 24Document Title
Thankyou