Cloud Computing Security
for Tenants
JANUARY 2019
Introduction
This document 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.
Assessors1 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 2.
Cloud computing, as defined by the U.S. National Institute of Standards and Technology3, 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 4 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 document 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 document 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 document, sensitive data is defined as OFFICIAL: Sensitive. Highly
sensitive data is defined as data classified as PROTECTED. Additionally, this document 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.
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Cloud Computing Security for Tenants
Risk
Reference
Mitigations
1 - General
Use a cloud service that has been assessed5, certified and accredited against the ISM6 at the appropriate classification level, addressing mitigations in the document Cloud Computing Security for Cloud Service Providers 7.
2 - General
Implement security governance involving senior management directing and coordinating security-related activities including robust change management8, 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 metadata9 10.
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.
6 - General
Use a corporately approved and secured computer, multi-factor authentication, a strong passphrase, least access privileges15 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.
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.
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.
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 27.
Cloud service unavailable due to tenant’s inadequate network connectivity to the cloud service
14 - General
Implement adequately high bandwidth28, 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.
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.
1 - IaaS
Securely configure, harden and maintain VMs with host based security controls30 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 segregation31 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 tenant32 33 34.
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.
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 tenant35 36 37.
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.
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.
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
Tenant’s data compromised in transit by malicious third party
Tenant’s cloud service account credentials compromised by malicious third party
11 12 13 14
Tenant’s data compromised by malicious CSP staff or malicious third party
Tenant’s data compromised by another malicious/compromised
Tenant’s data unavailable due to corruption,
deletion26,
tenant16 17 18 19 20 21 22 23 24 25
or CSP terminating the account/service
Financial consequences of a genuine spike in demand or bandwidth/CPU denial of service
Most Effective Risk Mitigations Particularly Relevant to IaaS
Tenant’s Virtual Machine (VM) compromised by malicious third party29
Most Effective Risk Mitigations Particularly Relevant to PaaS
Tenant’s web application compromised by malicious third party
Most Effective Risk Mitigations Particularly Relevant to SaaS
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Further information
The Australian Government Information Security Manual (ISM)38 provides guidance for mitigations such as ASDapproved cryptographic controls. The Strategies to Mitigate Cyber Security Incidents 39 provide additional guidance
for mitigations such as prompt patching, prompt log analysis, securing computers, as well as network segmentation and
segregation.
Commonwealth entities applying the ISM must only use outsourced cloud services listed on the Australian Cyber
Security Centre’s Certified Cloud Services List (CCSL)40. Commonwealth entities need to perform accreditation
activities, including reviewing the certification report, 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 41.
Additional cloud computing security advice is available at https://www.acsc.gov.au/infosec/cloudsecurity.htm.
Contact details
Organisations or individuals with questions regarding this advice can contact the ACSC by emailing
asd.assist@defence.gov.au or calling 1300 CYBER1 (1300 292 371).
https://www.acsc.gov.au/infosec/irap.htm
https://www.acsc.gov.au/infosec/cloudsecurity.htm
3 https://csrc.nist.gov/publications/detail/sp/800-145/final
4 https://www.protectivesecurity.gov.au/governance/security-planning-risk-management/Pages/default.aspx
5
https://www.acsc.gov.au/infosec/irap.htm
6
https://www.acsc.gov.au/infosec/ism/
7
https://www.acsc.gov.au/infosec/cloudsecurity.htm
8 https://isc.sans.org/diary/Who+inherits+your+IP+address%3F/18365
9 https://securosis.com/blog/cloud-forensics-101
10 https://www.browserstack.com/attack-and-downtime-on-9-November
11
https://www.browserstack.com/attack-and-downtime-on-9-November
12 https://www.darkreading.com/attacks-breaches/code-hosting-service-shuts-down-after-cyber-attack/d/did/1278743
13 https://securosis.com/blog/my-500-cloud-security-screwup
14 https://www.theregister.co.uk/2014/05/20/github_oversharing_snafu_nbc_private_keys/
15 https://www.acsc.gov.au/publications/protect/Restricting_Admin_Privileges.pdf
16 https://www.cvedetails.com/vulnerability-list.php?vendor_id=252&product_id=22134&page=1&order=3
17 https://docs.microsoft.com/en-au/security-updates/SecurityBulletins/2013/ms13-092
18 https://www.cvedetails.com/vulnerability-list.php?vendor_id=6276&page=1&order=3
19 https://access.redhat.com/errata/RHSA-2014:0420
20
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-0311
21 https://blog.docker.com/2014/06/docker-container-breakout-proof-of-concept-exploit/
22 https://opensource.com/business/14/7/docker-security-selinux
23 https://www.theregister.co.uk/2014/11/25/docker_vulnerabilities/
24 https://www.theregister.co.uk/2014/12/12/docker_vulnerability/
25 https://seclists.org/fulldisclosure/2014/Dec/26
26
https://www.darkreading.com/attacks-breaches/code-hosting-service-shuts-down-after-cyber-attack/d/did/1278743
27 https://www.finance.gov.au/archive/cloud/
28 https://www.zdnet.com/article/terra-firma-goes-with-private-cloud-for-virtual-desktops/
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2
3
29
https://www.browserstack.com/attack-and-downtime-on-9-November
https://www.acsc.gov.au/infosec/top35mitigationstrategies.htm
31 https://www.acsc.gov.au/publications/protect/Network_Segmentation_Segregation.pdf
32 https://www.microsoft.com/en-us/sdl
33 https://www.sans.org/top25-software-errors
34 https://www.owasp.org/index.php/OWASP_Proactive_Controls
35
https://www.microsoft.com/en-us/sdl
36
https://www.sans.org/top25-software-errors
37
https://www.owasp.org/index.php/OWASP_Proactive_Controls
38
https://www.acsc.gov.au/infosec/ism/
39
https://www.acsc.gov.au/infosec/top35mitigationstrategies.htm
40 https://www.acsc.gov.au/infosec/irap/certified_clouds.htm
41 https://www.finance.gov.au/archive/cloud/
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