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Cloud Computing Security for Tenants

This publication discusses the risks associated with cloud computing and provides guidance on suitable mitigation strategies. This publication is specifically tailored for tenants of cloud services.

First published 2014; updated 2015 and 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.

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 by the US National Institute of Standards and Technology, 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 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.

Further information

The Australian Government Information Security Manual (ISM) provides guidance for mitigations such as ASD-approved cryptographic controls. The Strategies to Mitigate Cyber Security Incidents 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). 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.

Additional cloud computing security advice is available at Cloud Computing Security.

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).

Cloud Computing Security for Tenants

Most effective risk mitigations generally relevant to all types of cloud services

Risk Reference Mitigations
Overarching failure to maintain the confidentiality, integrity and availability of the tenant’s data 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 Providers7.
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 metadata 9,10.
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 11,12,13,14 6 - General Use a corporately approved and secured computer, multi-factor authentication, a strong passphrase, least access privileges15and 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 16,17,18,19,20,21,22,23,24,25 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, deletion26, 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 risks27.
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.
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

Risk Reference Mitigations
Tenant’s Virtual Machine (VM) compromised by malicious third party29 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 all 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 tenant 32,33,34.
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.

Most effective risk mitigations particularly relevant to PaaS

Risk Reference Mitigations
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 35,36,37.
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.

Most effective risk mitigations particularly relevant to SaaS

Risk Reference Mitigations
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.

Footnotes

  1. ASD ACSC: Information Security Registered Assessors Program (IRAP)
  2. ASD ACSC: Cloud Computing Security
  3. NIST Special Publication 800-145: NIST Definition of Cloud Computing
  4. Attorney-General's Department: Protective Security Policy Framework - Security planning and risk management
  5. ASD ACSC: Information Security Registered Assessors Program (IRAP)
  6. ASD ACSC: Australian Government Information Security Manual
  7. ASD ACSC: Cloud Computing Security
  8. SANS Institute InfoSec Handlers Diary Blog: Who Inherits Your IP Address?
  9. Securosis: Cloud Forensics 101
  10. BrowserStack: Apologies for the downtime, but we're coming back stronger
  11. BrowserStack: Apologies for the downtime, but we're coming back stronger
  12. Dark Reading: Code Hosting Service Shuts Down After Cyber Attack
  13. Securosis: My $500 Cloud Security Screwup
  14. The Register: US giant NBC 'leaks' PRIVATE Amazon keys in Github Glenn gaffe
  15. ASD ACSC: Restricting Administrative Privileges
  16. CVE Details: Vmware Esxi: Security Vulnerabilities
  17. Microsoft Security Bulletin MS13-092: Vulnerability in Hyper-V Could Allow Elevation of Privilege
  18. CVE: XEN Security Vulnerabilities
  19. Red Hat: qemu-kvm security update
  20. CVE: CVE-2013-0311
  21. Docker: Docker Container Breakout Proof-of-Concept Exploit
  22. OpenSource.com: Are Docker containers really secure?
  23. The Register: How secure is Docker? If you're not running version 1.3.2, NOT VERY
  24. The Register: Batten down the patches: New vuln found in Docker container tech
  25. SecLists.org: Google App Engine Java security sandbox bypasses
  26. Dark Reading: Code Hosting Service Shuts Down After Cyber Attack
  27. Department of Finance: Cloud Computing
  28. ZDNet: Terra Firma goes with private cloud for virtual desktops
  29. BrowserStack: Apologies for the downtime, but we're coming back stronger
  30. ASD ACSC: Strategies to Mitigate Cyber Security Incidents
  31. ASD ACSC: Network Segmentation and Segregation
  32. Microsoft: Security Development Lifecycle
  33. SANS Institute: Top 25 Most Dangerous Software Errors
  34. Open Web Application Security Project: OWASP Proactive Controls
  35. Microsoft: Security Development Lifecycle
  36. SANS Institute: Top 25 Most Dangerous Software Errors
  37. Open Web Application Security Project: OWASP Proactive Controls
  38. ASD ACSC: Australian Government Information Security Manual
  39. ASD ACSC: Strategies to Mitigate Cyber Security Incidents
  40. ASD ACSC: Certified Cloud Services List
  41. Department of Finance: Cloud Computing (archived)
Date
January 1st, 2019