Network Working Group J. Preuß Mattsson
Internet-Draft G. Selander
Intended status: Informational Ericsson
Expires: 15 August 2022 C. Amsüss
Energy Harvesting Solutions
11 February 2022
Amplification Attacks Using the Constrained Application Protocol (CoAP)
draft-mattsson-t2trg-amplification-attacks-00
Abstract
Protecting Internet of Things (IoT) devices against attacks is not
enough. IoT deployments need to make sure that they are not used for
Distributed Denial-of-Service (DDoS) attacks. DDoS attacks are
typically done with compromised devices or with amplification attacks
using a spoofed source address. This document gives examples of
different theoretical amplification attacks using the Constrained
Application Protocol (CoAP). The goal with this document is to raise
awareness and to motivate generic and protocol-specific
recommendations on the usage of CoAP. Some of the discussed attacks
can be mitigated by not using NoSec or by using the Echo option.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 15 August 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Amplification Attacks using CoAP . . . . . . . . . . . . . . 3
2.1. Simple Amplification Attacks . . . . . . . . . . . . . . 4
2.2. Amplification Attacks using Observe . . . . . . . . . . . 5
2.3. Amplification Attacks using Group Requests . . . . . . . 7
2.4. MITM Amplification Attacks . . . . . . . . . . . . . . . 8
3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Informative References . . . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
One important protocol used to interact with Internet of Things (IoT)
sensors and actuators is the Constrained Application Protocol (CoAP)
[RFC7252]. CoAP can be used without security in the so called NoSec
mode but any Internet-of-Things (IoT) deployment valuing security and
privacy would use a security protocol such as DTLS
[I-D.ietf-tls-dtls13], TLS [RFC8446], or OSCORE [RFC8613] to protect
CoAP, where the choice of security protocol depends on the transport
protocol and the presence of intermediaries. The use of CoAP over
UDP and DTLS is specified in [RFC7252] and the use of CoAP over TCP
and TLS is specified in [RFC8323]. OSCORE protects CoAP end-to-end
with the use of COSE [RFC8152] and the CoAP Object-Security option
[RFC8613] and can therefore be used over any transport. Group OSCORE
[I-D.ietf-core-oscore-groupcomm] can be used to protect CoAP Group
Communication [I-D.ietf-core-groupcomm-bis].
Protecting Internet of Things (IoT) devices against attacks is not
enough. IoT deployments need to make sure that they are not used for
Distributed Denial-of-Service (DDoS) attacks. DDoS attacks are
typically done with compromised devices or with amplification attacks
using a spoofed source address. DDoS attacks is a huge and growing
problem for services and critical infrastucture [DDoS-Infra].
The document gives examples of different theoretical amplification
attacks using CoAP. When transported over UDP, the CoAP NoSec mode
is susceptible to source IP address spoofing and as a single request
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can result in multiple responses from multiple servers, CoAP can have
very large amplification factors. The goal with this document is to
raise awareness and to motivate generic and protocol-specific
recommendations on the usage of CoAP.
Some of the discussed attacks can be mitigated by not using NoSec or
by using the Echo option [I-D.ietf-core-echo-request-tag].
2. Amplification Attacks using CoAP
In a Denial-of-Service (DoS) attack, an attacker sends a large number
of requests or responses to a target endpoint. The denial-of-service
might be caused by the target endpoint receiving a large amount of
data, sending a large amount of data, doing heavy processing, or
using too much memory, etc. In a Distributed Denial-of-Service
(DDoS) attack, the request or responses come from a large number of
sources.
In an amplification attack, the amplification factor is the ratio
between the total size of the data sent to the target and the total
size of the data sent by the attacker. In the attacks described in
this section, the attacker sends one or more requests, and the target
receives one or more responses. An amplification attack alone can be
a denial-of-service attack on a CoAP server by making it send a large
amount of data. But often amplification attacks are combined with
the attacker spoofing the source IP address of the targeted victim.
By requesting as much information as possible from several servers an
attacker can multiply the amount of traffic and create a distributed
denial-of-service attack on the target. When transported over UDP,
the CoAP NoSec mode is susceptible to source IP address spoofing.
Amplification attacks with CoAP are unfortunately not only theory.
Powerful CoAP amplification attacks made headlines in 2018, reaching
55 Gbps on average, and with the largest one clocking at 320 Gbps
[DDoS-ZDNET]. But in 2019, they were hardly seen anymore
[DDoS-2019]. In 2020, the FBI cyber division mentioned CoAP in a
public notification warning that cyber actors are increasingly likely
to abuse network protocols for DDoS attacks [DDoS-FBI]. CoAP
amplification attacks made a comeback in 2020 and CoAP was behind a
significant part of global DDoS attacks in Q4 2020 and Q1 2021, but
not at all in Q2 and Q3 of 2021 [DDoS-2021]. It seems unclear
exactly how the attacks were done, why they stopped, and how likely
CoAP amplifications attacks are to come back in the future.
The following sections give examples of different theoretical
amplification attacks using CoAP.
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2.1. Simple Amplification Attacks
An amplification attack using a single response is illustrated in
Figure 1. If the response is c times larger than the request, the
amplification factor is c.
Client Foe Server
| | |
| +----->| Code: 0.01 (GET)
| | GET | Uri-Path: random quote
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Payload: "just because you own half the county
| | | doesn't mean that you have the power
| | | to run the rest of us. For twenty-
| | | three years, I've been dying to tell
| | | you what I thought of you! And now...
| | | well, being a Christian woman, I can't
| | | say it!"
Figure 1: Amplification attack using a single response
An attacker can increase the bandwidth by sending several GET
requests. An attacker can also increase or control the amplification
factor by creating or updating resources. By creating new resources,
an attacker can increase the size of /.well-known/core. An
amplification attack where the attacker influences the amplification
factor is illustrated in Figure 2.
Client Foe Server
| | |
| +----->| Code: 0.02 (POST)
| | POST | Uri-Path: /member/
| | | Payload: hampsterdance.hevc
| | |
.... ....
| +----->| Code: 0.02 (GET)
| | GET | Uri-Path: /member/
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Payload: hampsterdance.hevc
| | |
| +----->| Code: 0.02 (GET)
| | GET | Uri-Path: /member/
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Payload: hampsterdance.hevc
.... ....
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Figure 2: Amplification attack using several requests and a chosen
amplification factor
2.2. Amplification Attacks using Observe
Amplification factors can be significantly worse when combined with
observe [RFC7641] and group requests [I-D.ietf-core-groupcomm-bis].
As a single request can result in multiple responses from multiple
servers, the amplification factors can be very large.
An amplification attack using observe is illustrated in Figure 3. If
each notification response is c times larger than the registration
request and each request results in n notifications, the
amplification factor is c * n. By registering the same client
several times using different Tokens or port numbers, the bandwidth
can be increased. By updating the observed resource, the attacker
may trigger notifications and increase the size of the notifications.
By using conditional attributes
[I-D.ietf-core-conditional-attributes] an attacker may increase the
frequency of notifications and therefore the amplification factor.
The maximum period attribute pmax indicates the maximum time, in
seconds, between two consecutive notifications (whether or not the
resource state has changed). If it is predictable when notifications
are sent as confirmable and which Message ID are used the
acknowledgements may be spoofed.
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Client Foe Server
| | |
| +----->| Code: 0.01 (GET)
| | GET | Token: 0x83
| | | Observe: 0
| | | Uri-Path: temperature
| | | Uri-Query: pmax="0.1"
| | |
| +----->| Code: 0.01 (GET)
| | GET | Token: 0x84
| | | Observe: 0
| | | Uri-Path: temperature
| | | Uri-Query: pmax="0.1"
| | |
.... ....
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x83
| | | Observe: 217362
| | | Payload: "299.7 K"
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x84
| | | Observe: 217362
| | | Payload: "299.7 K"
| | |
.... ....
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x83
| | | Observe: 217363
| | | Payload: "299.7 K"
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x84
| | | Observe: 217363
| | | Payload: "299.7 K"
.... ....
Figure 3: Amplification attack using observe, registering the
same client several times, and requesting notifications at least
10 times every second
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2.3. Amplification Attacks using Group Requests
An amplification attack using a group request is illustrated in
Figure 4. The group request is sent over multicast or broadcast and
in this case a single request results in m responses from m different
servers. If each response is c times larger than the request, the
amplification factor is c * m. Note that the servers usually do not
know the variable m.
Client Foe Server
| | |
| +----->| Code: 0.01 (GET)
| | GET | Token: 0x69
| | | Uri-Path: </c>
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x69
| | | Payload: { 1721 : { ...
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x69
| | | Payload: { 1721 : { ...
| | |
.... ....
Figure 4: Amplification attack using multicast
An amplification attack using a multicast request and observe is
illustrated in Figure 5. In this case a single request results in n
responses each from m different servers giving a total of n * m
responses. If each response is c times larger than the request, the
amplification factor is c * n * m.
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Client Foe Server
| | |
| +----->| Code: 0.01 (GET)
| | GET | Token: 0x44
| | | Observe: 0
| | | Uri-Path: temperature
| | | Uri-Query: pmax="0.1"
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x44
| | | Observe: 217
| | | Payload: "301.2 K"
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x44
| | | Observe: 363
| | | Payload: "293.4 K"
| | |
.... ....
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x44
| | | Observe: 218
| | | Payload: "301.2 K"
| | |
|<------------+ Code: 2.05 (Content)
| | 2.05 | Token: 0x44
| | | Observe: 364
| | | Payload: "293.4 K"
| | |
.... ....
Figure 5: Amplification attack using multicast and observe
2.4. MITM Amplification Attacks
TLS and DTLS without Connection ID [I-D.ietf-tls-dtls-connection-id]
validate the IP address and port of the other peer, binds them to the
connection, and do not allow them to change. DTLS with Connection ID
allows the IP address and port to change at any time. As the source
address is not protected, an MITM attacker can change the address.
Note that an MITM attacker is a more capable attacker then an
attacker just spoofing the source address. It can be discussed if
and how much such an attack is reasonable for DDoS, but DTLS 1.3
states that "This attack is of concern when there is a large
asymmetry of request/response message sizes." [I-D.ietf-tls-dtls13].
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DTLS 1.2 with Connection ID [I-D.ietf-tls-dtls-connection-id]
requires that "the receiver MUST NOT replace the address" unless
"there is a strategy for ensuring that the new peer address is able
to receive and process DTLS records" but does not give more details
than that. It seems like the receiver can start using the new peer
address and test that it is able to receive and process DTLS records
at some later point. DTLS 1.3 with Connection ID requires that
"implementations MUST NOT update the address" unless "they first
perform some reachability test" but does not give more details than
that. OSCORE [RFC8613] does not discuss address updates, but it can
be assumed that most servers send responses to the address it
received the request from without any reachability test. A
difference between (D)TLS and OSCORE is that in DTLS the updated
address is used for all future records, while in OSCORE a new address
is only used for responses to a specific request.
An MITM amplification attack updating the client's source address in
an observe registration is illustrated in Figure 6. This attack is
possible in OSCORE and DTLS with Connection ID. The server will send
notifications to the Victim until it at some unspecified point
requires an acknowledgement [RFC7641]. In DTLS 1.2 the reachability
test might be done at a later point. In OSCORE a reachability test
is likely not done.
Client Victim Foe Server
| | | |
+------------>S----->| Code: 0.01 (GET)
| GET | | | Observe: 0
| | | | Uri-Path: humidity
| | | |
|<------------D<-----+ Reachability test (DTLS)
+------------>S----->|
| | | |
.... .... ....
| |<------------+ Code: 2.05 (Content)
| | | 2.05 | Observe: 263712
| | | | Payload: "68 %"
| | | |
| |<------------+ Code: 2.05 (Content)
| | | 2.05 | Observe: 263713
| | | | Payload: "69 %"
.... .... ....
Figure 6: MITM Amplification attack by updating the client's
source address in a observe registration request
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Where 'S' means the MITM attacker is changing the source address of
the message and 'D' means the MITM attacker is changing the
destination address of the message.
An MITM amplification attack updating the server's source address is
illustrated in Figure 7. This attack is possible in DTLS with
Connection ID. In DTLS 1.2 the reachability test might be done at a
later point.
Client Foe Victim Server
| | | |
+------------------->| Code: 0.01 (POST)
| POST | | | Uri-Path: video/
| | | |
|<-----S<------------| Code: 2.01 (Created)
| | | 2.01 |
| | | |
+----->D------------>| Reachability test (DTLS)
|<-----S<------------+
| | | |
.... .... ....
+------------>| | Code: 0.01 (POST)
| POST | | | Uri-Path: video/
| | | | Payload: survailance_1139.hevc
| | | |
+------------>| | Code: 0.01 (POST)
| POST | | | Uri-Path: video/
| | | | Payload: survailance_1140.hevc
.... .... ....
Figure 7: MITM Amplification attack by updating the server's
source address in a response
3. Summary
CoAP has always considered amplification attacks, but most of the
requirements in [RFC7252], [RFC7641],
[I-D.ietf-core-echo-request-tag], and [I-D.ietf-core-groupcomm-bis]
are "SHOULD" instead of "MUST", it is undefined what a "large
amplification factor" is, [RFC7641] does not specify how many
notifications that can be sent before a potentially spoofable
acknowledgement must be sent, and in several cases the "SHOULD" level
is further softened by "If possible" and "generally".
[I-D.ietf-core-conditional-attributes] does not have any
amplification attack considerations.
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QUIC [RFC9000] mandates that "an endpoint MUST limit the amount of
data it sends to the unvalidated address to three times the amount of
data received from that address" without any exceptions. This
approach should be seen as current best practice.
While it is clear when a QUIC implementation violates the requirement
in [RFC9000], it is not clear when a CoAP implementation violates the
requirement in [RFC7252], [RFC7641],
[I-D.ietf-core-echo-request-tag], and [I-D.ietf-core-groupcomm-bis].
In CoAP, an address can be validated with a security protocol or by
using the Echo Option [I-D.ietf-core-echo-request-tag]. Restricting
the bandwidth per server is not enough as the number of servers the
attacker can use is typically unknown. For multicast requests, anti-
amplification limits and the Echo Option do not really work unless
the number of servers sending responses is known. Even if the
responses have the same size as the request, the amplification factor
from m servers is m, where m is typically unknown. While DoS attacks
from CoAP servers accessible over the Internet pose the largest
threat, an attacker on a local network (e.g, a compromised node)
might use local CoAP servers to attack targets on the Internet or on
the local network.
4. Security Considerations
The whole document can be seen as security considerations for CoAP.
5. IANA Considerations
This document has no actions for IANA.
6. Informative References
[DDoS-2019]
"DDoS Attacks 2019: A look back at the Developments over
the Year", Link11 , December 2019,
<https://www.link11.com/en/blog/threat-landscape/ddos-
attacks-2019-a-look-back-at-the-developments-over-the-
year/>.
[DDoS-2021]
"Quarterly DDoS and Application Attack Report", Radware ,
October 2021,
<https://www.radware.com/2021q3-ddos-report/>.
[DDoS-FBI] "Private Industry Notification", FBI Cyber Division , July
2020, <https://image.communications.cyber.nj.gov/lib/
fe3e15707564047c7c1270/m/2/FBI+PIN+-+7.21.2020.pdf>.
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[DDoS-Infra]
"Critical Infrastructure Under Attack", Dark Reading ,
November 2021, <https://www.darkreading.com/attacks-
breaches/critical-infrastructure-under-attack-/a/
d-id/1340960>.
[DDoS-ZDNET]
"The CoAP protocol is the next big thing for DDoS
attacks", ZDNet , December 2018,
<https://www.zdnet.com/article/the-coap-protocol-is-the-
next-big-thing-for-ddos-attacks/>.
[I-D.ietf-core-conditional-attributes]
Koster, M., Soloway, A., and B. Silverajan, "Conditional
Attributes for Constrained RESTful Environments", Work in
Progress, Internet-Draft, draft-ietf-core-conditional-
attributes-01, 13 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-core-
conditional-attributes-01.txt>.
[I-D.ietf-core-echo-request-tag]
Amsüss, C., Mattsson, J. P., and G. Selander, "CoAP: Echo,
Request-Tag, and Token Processing", Work in Progress,
Internet-Draft, draft-ietf-core-echo-request-tag-14, 4
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-echo-request-tag-14.txt>.
[I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", Work in
Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
05, 25 October 2021, <https://www.ietf.org/archive/id/
draft-ietf-core-groupcomm-bis-05.txt>.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
and J. Park, "Group OSCORE - Secure Group Communication
for CoAP", Work in Progress, Internet-Draft, draft-ietf-
core-oscore-groupcomm-13, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-core-oscore-
groupcomm-13.txt>.
[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J. P., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
Progress, Internet-Draft, draft-ietf-lake-edhoc-12, 20
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
lake-edhoc-12.txt>.
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[I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., Fossati, T., and A. Kraus,
"Connection Identifiers for DTLS 1.2", Work in Progress,
Internet-Draft, draft-ietf-tls-dtls-connection-id-13, 22
June 2021, <https://www.ietf.org/archive/id/draft-ietf-
tls-dtls-connection-id-13.txt>.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-43, 30 April 2021,
<https://www.ietf.org/archive/id/draft-ietf-tls-
dtls13-43.txt>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/info/rfc8323>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
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[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
Acknowledgements
The authors would like to thank Carsten Bormann, Klaus Hartke, Jaime
Jiménez, Ari Keränen, Matthias Kovatsch, Achim Kraus, Sandeep Kumar,
and András Méhes for their valuable comments and feedback.
Authors' Addresses
John Preuß Mattsson
Ericsson AB
SE-164 80 Stockholm
Sweden
Email: john.mattsson@ericsson.com
Göran Selander
Ericsson AB
SE-164 80 Stockholm
Sweden
Email: goran.selander@ericsson.com
Christian Amsüss
Energy Harvesting Solutions
Email: c.amsuess@energyharvesting.at
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