Introduction This publication is designed to assist an organisation’s cyber security team, cloud architects and business representatives to jointly perform a risk assessment and use cloud services securely. Assessors validating the security posture of a cloud service offered by Cloud Service Providers (CSPs), and CSPs that want to offer secure cloud services, should refer to the companion document Cloud Computing Security for Cloud Service Providers Cloud computing as defined in National Institute of Standards and Technology (NIST) Special Publication 800-145, The NIST Definition of Cloud Computing, offers organisations potential benefits such as improved business outcomes. Mitigating the risks associated with using cloud services is a responsibility shared between the organisation (referred to as the ‘tenant’) and the Cloud Service Provider, including their subcontractors (referred to as the ‘CSP’). However, organisations are ultimately responsible for protecting their data and ensuring its confidentiality, integrity and availability. Organisations need to perform a risk assessment and implement associated mitigations before using cloud services. Risks vary depending on factors such as the sensitivity and criticality of data to be stored or processed, how the cloud service is implemented and managed, how the organisation intends to use the cloud service, and challenges associated with the organisation performing timely incident detection and response. Organisations need to compare these risks against an objective risk assessment of using in-house computer systems which might be poorly secured, have inadequate availability or be unable to meet modern business requirements. The scope of this publication covers Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS), provided by a CSP as part of a public cloud, community cloud and, to a lesser extent, a hybrid cloud or outsourced private cloud. This publication focuses on the use of cloud services for storing or processing sensitive and highly sensitive data. For Commonwealth entities, and for the purposes of this publication, sensitive data is defined as OFFICIAL: Sensitive. Highly sensitive data is defined as data classified as PROTECTED. Additionally, this publication can assist with mitigating risks to the availability and integrity of non-sensitive data, defined for Commonwealth entities as unclassified publicly releasable data. Mitigations are listed in no particular order of prioritisation. Cloud Computing Security for Tenants Risk Reference Mitigations Most Effective Risk Mitigations Generally Relevant to All Types of Cloud Services Overarching failure to maintain the confidentiality, integrity and availability of the tenant’s data 1 - General Use a cloud service that has been assessed against the ISM  at the appropriate classification level, addressing mitigations in the document Cloud Computing Security for Cloud Service Providers . 2 - General Implement security governance involving senior management directing and coordinating security-related activities including robust change management, as well as having technically skilled staff in defined security roles. 3 - General Implement and annually test an incident response plan covering data spills, electronic discovery, and how to obtain and analyse evidence e.g. time-synchronised logs, hard disk images, memory snapshots and metadata  . Tenant’s data compromised in transit by malicious third party 4 - General Use ASD approved cryptographic controls to protect data in transit between the tenant and the CSP e.g. application layer TLS or IPsec VPN with approved algorithms, key length and key management. 5 - General Use ASD approved cryptographic controls to protect data at rest on storage media in transit via post/courier between the tenant and the CSP when transferring data as part of on-boarding or off-boarding. Tenant’s cloud service account credentials compromised by malicious third party     6 - General Use a corporately approved and secured computer, multi-factor authentication, a strong passphrase, least access privileges  and encrypted network traffic to administer (and, if appropriate, access) the cloud service. 7 - General Protect authentication credentials e.g. avoid exposing Application Programming Interface (API) authentication keys placed on insecure computers or in the source code of software that is accessible to unauthorised third parties. 8 - General Obtain and promptly analyse detailed time-synchronised logs and real-time alerts for the tenant’s cloud service accounts used to access, and especially to administer, the cloud service. Tenant’s data compromised by malicious CSP staff or malicious third party 9 - General Obtain and promptly analyse detailed time-synchronised logs and real-time alerts generated by the cloud service used by the tenant e.g. operating system, web server and application logs. 10 - General Avoid providing the CSP with account credentials (or the ability to authorise access) to sensitive systems outside of the CSP’s cloud such as systems on the tenant’s corporate network. Tenant’s data compromised by another malicious/compromised tenant          11 - General Use multi-tenancy mechanisms provided by the CSP e.g. to separate the tenant’s web application and network traffic from other tenants, use the CSP’s hypervisor virtualisation instead of web server software virtual hosting. Tenant’s data unavailable due to corruption, deletion , or CSP terminating the account/service 12 - General Perform up-to-date encrypted backups in a format avoiding CSP lock-in, stored offline at the tenant’s premises or at a second CSP requiring multi-factor authentication to modify/delete data. Annually test the recovery process. Tenant’s data unavailable or compromised due to CSP bankruptcy or other legal action 13 - General Contractually retain legal ownership of tenant data. Perform a due diligence review of the CSP’s contract and financial viability as part of assessing privacy and legal risks. Cloud service unavailable due to tenant’s inadequate network connectivity to the cloud service 14 - General Implement adequately high bandwidth , low latency, reliable network connectivity between the tenant (including the tenant’s remote users) and the cloud service to meet the tenant’s availability requirements. Cloud service unavailable due to CSP error, planned outage, failed hardware or act of nature 15 - General Use a cloud service that meets the tenant’s availability requirements. Assess the Service Level Agreement penalties, and the number, severity, recency and transparency of the CSP’s scheduled and unscheduled outages. 16 - General Develop and annually test a disaster recovery and business continuity plan to meet the tenant’s availability requirements e.g. where feasible for simple architectures, temporarily use cloud services from an alternative CSP. Financial consequences of a genuine spike in demand or bandwidth/CPU denial of service 17 - General Manage the cost of a genuine spike in demand or denial of service via contractual spending limits, denial of service mitigation services and judicious use of the CSP’s infrastructure capacity e.g. limits on automated scaling. Most Effective Risk Mitigations Particularly Relevant to IaaS Tenant’s Virtual Machine (VM) compromised by malicious third party  1 - IaaS Securely configure, harden and maintain VMs with host-based security controls  e.g. firewall, intrusion prevention system, logging, antivirus software, and prompt patching of software that the tenant is responsible for. 2 - IaaS Use a corporately approved and secured computer to administer VMs requiring access from the tenant’s IP address, encrypted traffic, and a SSH/RDP PKI key pair protected with a strong passphrase. 3 - IaaS Only use VM template images provided by trusted sources, to help avoid the accidental or deliberate presence of malware and backdoor user accounts. Protect the tenant’s VM template images from unauthorised changes. 4 - IaaS Implement network segmentation and segregation  e.g. n-tier architecture, using host-based firewalls and CSP’s network access controls to limit inbound and outbound VM network connectivity to only required ports/protocols. 5 - IaaS Utilise secure programming practices for software developed by the tenant   . Cloud service unavailable due to CSP error, planned outage, failed hardware or act of nature 6 - IaaS Architect to meet availability requirements e.g. minimal single points of failure, data replication, automated failover, multiple availability zones, geographically separate data centres and real-time availability monitoring. Cloud service unavailable due to genuine spike in demand or bandwidth/CPU denial of service 7 - IaaS If high availability is required, implement clustering and load balancing, a Content Delivery Network for public web content, automated scaling with an adequate maximum scale value, and real-time availability monitoring. Most Effective Risk Mitigations Particularly Relevant to PaaS Tenant’s web application compromised by malicious third party 1 - PaaS Securely configure and promptly patch all software that the tenant is responsible for. 2 - PaaS Utilise secure programming practices for software developed by the tenant   . Cloud service unavailable due to CSP error, planned outage, failed hardware or act of nature 3 - PaaS Architect to meet availability requirements e.g. minimal single points of failure, data replication, automated failover, multiple availability zones, geographically separate data centres and real-time availability monitoring. Cloud service unavailable due to genuine spike in demand or bandwidth/CPU denial of service 4 - PaaS If high availability is required, implement clustering and load balancing, a Content Delivery Network for public web content, automated scaling with an adequate maximum scale value, and real-time availability monitoring. Most Effective Risk Mitigations Particularly Relevant to SaaS Tenant’s data compromised by malicious CSP staff or malicious third party 1 - SaaS Use security controls specific to the cloud service e.g. tokenisation to replace sensitive data with non-sensitive data, or ASD approved encryption of data (not requiring processing) and avoid exposing the decryption key. Cloud service unavailable due to genuine spike in demand or bandwidth/CPU denial of service 2 - SaaS If high availability is required, where possible and appropriate, implement additional cloud services providing layered denial of service mitigation, where these cloud services might be provided by third party CSPs. Further information The Information Security Manual is a cyber security framework that organisations can apply to protect their systems and data from cyber threats. The advice in the Strategies to Mitigate Cyber Security Incidents, along with its Essential Eight, complements this framework. Commonwealth entities need to assess cloud services to determine whether the residual risk of their proposed use of a cloud service is acceptable. Commonwealth entities also need to perform an additional due diligence review of financial, privacy, data ownership, data sovereignty and legal risks. Contact details If you have any questions regarding this guidance you can write to us or call us on 1300 CYBER1 (1300 292 371).