ISO/IEC 27035-3:2020

INTERNATIONAL ISO/IEC
STANDARD 27035-3
First edition
2020-09
Information technology —
Information security incident
management —
Part 3:
Guidelines for ICT incident response
operations
Technologies de l'information — Gestion des incidents de sécurité de
l'information —
Partie 3: Lignes directrices relatives aux opérations de réponse aux
incidents TIC
Reference number
ISO/IEC 27035-3:2020(E)
©
ISO/IEC 2020

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ISO/IEC 27035-3:2020(E)

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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO/IEC 27035-3:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Overview . 3
5.1 General . 3
5.2 Structure of this document . 3
6 Common types of attacks . 5
7 Incident detection operations . 6
7.1 Point of contact . 6
7.2 Monitoring and detection . 7
7.3 Common ways detection is performed . 8
7.3.1 Monitoring public sources to look for potential reports (and threats) . 8
7.3.2 Validation of external source data . 9
7.3.3 Proactive detection .10
7.3.4 Reactive methods .10
8 Incident notification operations .11
8.1 Overview .11
8.2 Immediate incident notification .12
8.2.1 Incident reporting forms .12
8.2.2 Critical information that incident reports should (ideally) contain .12
8.2.3 Methods to receive reports .12
8.2.4 Considerations for escalation .13
8.3 PoC structure .13
8.3.1 Incident response operation notification if a single PoC exists .13
8.3.2 Incident response operation notification if multiple PoCs exist.14
9 Incident triage operations .14
9.1 Overview .14
9.2 How triage is conducted .14
10 Incident analysis operations .15
10.1 Overview .15
10.2 Purpose of analysis .17
10.3 Intra-incident analysis .18
10.4 Inter-incident analysis .19
10.5 Analysis tools .20
10.6 Storing evidence and analysis results .20
11 Incident containment, eradication and recovery operations .21
11.1 Overview .21
11.2 Conducting the response for containment, eradication and recovery .21
11.2.1 Containment description .21
11.2.2 Containment goals .21
11.2.3 Common containment strategies .21
11.2.4 Issues associated with containment .22
11.3 Eradication .22
11.3.1 Eradication description.22
11.3.2 Eradication strategies .22
11.3.3 Issues associated with eradication .23
11.4 Recovery .23
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ISO/IEC 27035-3:2020(E)

11.4.1 Recovery description .23
11.4.2 Recovery strategies . .23
11.4.3 Issues associated with recovery .23
12 Incident reporting operations .23
12.1 Overview .23
12.2 How to establish reporting .24
12.3 How to establish external reporting, if required .25
12.4 Information sharing .26
12.5 Other reporting considerations .26
12.6 Types of reports .27
12.7 Methods for storing reports and analysts' knowledge .27
Annex A (informative) Example of the incident criteria based on information security
events and incidents .28
Bibliography .31
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ISO/IEC 27035-3:2020(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
A list of all parts in the ISO 27035 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/IEC 27035-3:2020(E)

Introduction
An information security incident can involve ICT or not. For example, information that spreads
unintentionally through the loss of paper documents can very well be a serious information security
incident, which requires incident reporting, investigation, containment, corrective actions and
management involvement. This type of incident management is often carried out, for example, by the
Chief Information Security Officer (CISO) within the organization. Guidance on the management of
such information security incidents can be found in ISO/IEC 27035-1. This document, however, only
considers incident response operations for ICT-related incidents, and not for information security
incidents related to paper documents or any other non-ICT incidents. Whenever the term "information
security" is used in this document, it is done so in the context of ICT-related information security.
The organizational structures for information security vary depending on the size and business field of
organizations. As various and numerous incidents occur and are increasing (such as network incidents,
e.g. intrusions, data breaches and hacking), higher concerns about information security have been
raised by organizations. A secure ICT environment set up to withstand various types of attacks (such
as DoS, worms and viruses) with network security equipment such as firewalls, intrusion detection
systems (IDSs) and intrusion prevention systems (IPSs) should be complemented with clear operating
procedures for incident handling, along with well-defined reporting structures within the organization.
To ensure confidentiality, integrity and availability of information and to handle incidents efficiently,
capabilities to conduct incident response operations is required. For this purpose, a computer security
incident response team (CSIRT) should be established to perform tasks such as monitoring, detection,
analysis and response activities for collected data or security events. These tasks may be assisted by
artificial intelligence tools and techniques.
This document supports the controls of ISO/IEC 27001:2013, Annex A, related to incident management.
Not all steps in this document are applicable since it depends on the particular incident. For example, a
smaller organization may not use all guidance in this document but can find it useful for organization
of their ICT-related incident operations especially if operating their own ICT environment. It can also
be useful for smaller organizations that have outsourced their IT operations to better understand the
requirements and execution of incident operations that they should expect from their ICT supplier(s).
This document is particularly useful to organizations providing ICT services that involve interactions
between organizations of incident operations in order to follow the same processes and terms.
This document also provides a better understanding on how incident operations relates to the users/
customers in order to define when and how such interaction needs to take place, even if this is not
specified.
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INTERNATIONAL STANDARD ISO/IEC 27035-3:2020(E)
Information technology — Information security incident
management —
Part 3:
Guidelines for ICT incident response operations
1 Scope
This document gives guidelines for information security incident response in ICT security operations.
This document does this by firstly covering the operational aspects in ICT security operations from a
people, processes and technology perspective. It then further focuses on information security incident
response in ICT security operations including information security incident detection, reporting, triage,
analysis, response, containment, eradication, recovery and conclusion.
This document is not concerned with non-ICT incident response operations such as loss of paper-based
documents.
This document is based on the “Detection and reporting” phase, the “Assessment and decision” phase
and the “Responses” phase of the “Information security incident management phases” model presented
in ISO/IEC 27035-1:2016.
The principles given in this document are generic and intended to be applicable to all organizations,
regardless of type, size or nature. Organizations can adjust the provisions given in this document
according to their type, size and nature of business in relation to the information security risk situation.
This document is also applicable to external organizations providing information security incident
management services.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 27000, Information technology — Security techniques — Information security management
systems — Overview and vocabulary
ISO/IEC 27035-1, Information technology — Security techniques — Information security incident
management — Part 1: Principles of incident management
ISO/IEC 27035-2, Information technology — Security techniques — Information security incident
management — Part 2: Guidelines to plan and prepare for incident response
ISO/IEC 27037, Information technology — Security techniques — Guidelines for identification, collection,
acquisition and preservation of digital evidence
ISO/IEC 27043, Information technology — Security techniques — Incident investigation principles and
processes
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 27000, ISO/IEC 27037,
ISO/IEC 27035-1, ISO/IEC 27035-2, ISO/IEC 27043 and the following apply.
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ISO/IEC 27035-3:2020(E)

ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
asset
anything that has value to an individual, an organization or a government
[SOURCE: ISO/IEC 27032:2012, 4.6]
3.2
computer security incident response team
CSIRT
team of security experts to support the handling of information security incidents
[SOURCE: ISO/IEC 27019:2017, 3.2]
3.3
investigation
systematic or formal process of inquiring into or researching, and examining facts or materials
associated with a matter
Note 1 to entry: A similar definition can be found in ISO/IEC 27042:2015, 3.10.
[SOURCE: ISO/IEC 27050:2017, 3.17, modified — Note 1 to entry has been added.]
3.1.4
response
incident response
action taken to protect and restore the normal operational conditions of information systems and the
information stored in it when an attack or intrusion occurs
[SOURCE: ISO/IEC 27039:2015, 2.24]
4 Abbreviated terms
ASCII American standard code for information interchange
CPU central processing unit
DNS domain name system or domain name service
DDoS distributed denial of service
DoS denial of service
ENISA European Union agency for network and information security
FAT file allocation table file system
FAT32 32-bit file allocation table file system
FIRST forum of incident response and security teams
HPFS high performance file system
HR human resources
ICT information and communication technology
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ISO/IEC 27035-3:2020(E)

IDS intrusion detection system
IoC indicators of compromise
IP internet protocol
IPS intrusion prevention system
ISP internet service provider
IT information technology
MD5 message digest 5 algorithm
NIST national institute for standards and technology
NTFS windows networking technology file system
OS operating system
PoC point of contact
SHA secure hashing algorithm
SIEM security information and event management system
URL universal resource locator
WAF web application firewall
XML extended mark-up language
5 Overview
5.1 General
ISO/IEC 27035-1 covers the following five main phases for information security incident management:
— Plan and prepare;
— Detection and reporting;
— Assessment and decision;
— Responses;
— Lessons learnt.
ISO/IEC 27035-2 covers two of these five phases in detail, i.e. "Plan and prepare" and "Lessons learnt".
This document covers the remaining three phases in detail. These three remaining phases are
collectively referred to as incident response operations, which are the focus in this document.
5.2 Structure of this document
The provisions in this document are based on the "Detection and reporting", "Assessment and decision"
and "Responses" phases of the “Information security incident management phases” model presented in
ISO/IEC 27035-1. Collectively, these phases are known as the incident response operation process.
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The phases within the incident response operation process (which are "Detection and reporting",
"Assessment and decision" and "Responses" as stipulated in ISO/IEC 27035-1) include the following:
— operations for incident identification;
— operations for incident assessment and qualification;
— operations for threat intelligence gathering;
— operations for incident containment, eradication and recovery;
— operations for incident analysis;
— operations for incident reporting.
The scope for incident response is defined in ISO/IEC 27035-1. Incident response operations should
be seen as a business process that enables an organization to remain in business. Specifically, an
incident response operation process is a collection of procedures aimed at identifying, responding to
and investigating potential security incidents in a way that minimizes their impact and support rapid
recovery.
ISO/IEC 27035-1 shows the five phases of information security incident management as Plan and
prepare, Detection and reporting, Assessment and decision, Responses and Lessons learnt. As
mentioned before, this document focuses on an incident response operation process. This process can
be characterized by a lifecycle of incident response operations which is represented by the inner phases
(detection, notification, triage, analysis, response, and reporting). These are represented in more detail
in Figure 1.
Figure 1 — Lifecycle of incident response operations
The lifecycle of incident response operations (detection, notification, triage, analysis, response,
and reporting) can be mapped to the five phases of information security incident management of
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ISO/IEC 27035-1 (Plan and prepare, Detection and reporting, Assessment and decision, Responses and
Lessons learnt) as shown in Table 1.
Table 1 — Mapping of the five phases of information security incident management in
ISO/IEC 27035-1 to the lifecycle of incident response operations in this document
Five phases of information security incident Lifecycle of ICT incident response operations in this
management in ISO/IEC 27035-1 document
Plan and prepare (None – covered in detail by ISO/IEC 27035–2)
Detection and reporting — Detection (presented in Clause 7, which links to ISO/
IEC 27035-1:2016, 5.3)
— Notification (presented in Clause 8, which links to ISO/
IEC 27035-1:2016, 5.3)
Assessment and decision — Triage (presented in Clause 9, which links to ISO/
IEC 27035-1:2016, 5.4)
— Analysis (presented in Clause 10, which links to ISO/
IEC 27035-1:2016, 5.4)
Responses — Response (presented in Clause 11, which links to ISO/
IEC 27035-1:2016, 5.5)
— Reporting (presented in Clause 12, which links to ISO/
IEC 27035-1:2016, 5.3)
Lessons learnt (None – covered in detail by ISO/IEC 27035-2)
NOTE The notion of reporting appears only once in ISO/IEC 27035-1:2016, 5.3. However, during the entire
lifecycle of incident response operations (as portrayed in this document), the notion of reporting appears twice:
once in Clause 7 and once in Clause 11. However, both instances of reporting map to ISO/IEC 27035-1:2016, 5.3.
To clarify, there are two distinct instances (occurrences) of reporting that take place during the entire lifecycle
of incident response operations as portrayed in this document. The first occurrence of reporting involves
the recording or registration of the fact that an incident has indeed occurred (as presented in Clause 7). The
second occurrence of reporting involves the recording of the outcome of the entire lifecycle of incident response
operations (as presented in Clause 11). In summary, the first occurrence reports to (notifies) a PoC that an
incident has indeed occurred, while the second occurrence reports on the outcome of the entire lifecycle of
incident response operations.
6 Common types of attacks
Incidents can happen in various ways and it is not practical to define all the incidents and prepare the
response manual for each type of incident. However, there are common attack types/sources that an
organization often encounter and should therefore be prepared to handle, such attacks efficiently.
Criteria should be set for security incidents according to the importance (priority) of information and
information systems, impact of each incident, damage scale, alarm ranking and its severity. See Annex A
for examples of such criteria.
The following is a non-exhaustive list of common attack types/sources that can be used as the basis for
defining incident handling procedures:
— external/removable media: an attack executed from removable media (e.g. flash drive, CD) or a
peripheral device;
— attrition: an attack that employs brute force methods to compromise, degrade, or destroy systems,
networks, or services (e.g. a DDoS intended to impair or deny access to a service or application; a
brute force attack against an authentication mechanis
...