ASD ISM 0635 Ensure network paths are isolated in CDSs
What it says
CDSs implement isolated upward and downward network paths.
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What it means
In plain EnglishSystems manage separate and secure network paths for upward and downward data movements to prevent security breaches.
This control is about keeping certain types of data moving in one direction only on a network, so it doesn't mix up with other data. By doing this, organisations protect themselves from unwanted data leaks or security breaches that could lead to sensitive information falling into the wrong hands.
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Why it matters
Failing to isolate upward and downward CDS network paths can enable data to traverse between domains, causing cross-contamination, data leakage and unauthorised access.
How to implement
The IT team should work on creating separate network pathways for data moving up (into secure areas) and data moving down (out to less secure areas).
This can be done by setting up separate cables or virtual paths within the network systems.
The network administrator should regularly test these pathways to ensure they are not mixing or allowing data to flow in unintended directions.
They can do this by running simulations and checking the flow of data packets.
The system manager should collaborate with security advisors to assess which data needs strict direction controls.
They should map out each type of data and ensure it uses the correct network path.
IT support should train staff on the importance of not using unofficial paths for data transfers.
This can be done through regular information sessions and reminders about data security policies.
Management should review the existing network configurations quarterly to verify that all changes in data flow needs are up to date.
They can do this by checking the latest network maps and configurations against current requirements.
Keep it running
Regularly validate CDS architecture keeps upward and downward paths physically/logically separated, and test permitted flows to confirm no unintended bridging or reverse transfer.
Evidence and audit
- Check 1 of 5What an auditor asks for
Ask for
The network configuration documents: Request the latest network setups showing the separate paths for upward and downward data.
Look at
The maps to confirm the paths are physically or logically separated.
Good evidence
Is a clear diagram showing two distinct paths with labels indicating the direction of data flow.
- Check 2 of 5What an auditor asks for
Ask for
Testing reports of the data pathways: Request documentation of recent tests or audits conducted on data paths.
Look at
The results to check if the tests confirm the paths are properly isolated.
Good evidence
Would be a report with successful test results and any actions taken to fix issues.
- Check 3 of 5What an auditor asks for
Ask for
Policies related to data flow control: Request the policy documents that outline how data flow is managed.
Look at
Sections detailing the separation of paths and staff responsibilities.
Good evidence
Is a current document signed off by management and accessible to all staff.
- Check 4 of 5What an auditor asks for
Ask for
Staff training records on data pathway usage: Request records of training sessions held regarding proper data transfer practices. Look into the attendee lists and feedback to verify comprehension and compliance.
Good evidence
Includes multiple sessions over time with a large majority of relevant staff attending.
- Check 5 of 5What an auditor asks for
Ask for
A risk assessment report: Request the document that evaluates the risks of data not following the correct paths.
Look at
The identified risks and mitigation measures.
Good evidence
Is a thorough report updated regularly to reflect any changes in the system or risks.
Mappings
Closest match in ISO/IEC 27001: A.8.22, Network segregation for security, which this control partially meets.
ISO/IEC 27001: 1 mapping
This control partially meets A.8.22.
ISM-0635 requires CDSs to implement isolated upward and downward network paths to separate data flows by direction and reduce the risk of cross-domain compromise. This relates to Annex A 8.22, which requires network segregation between groups of services, users and systems to enforce security boundaries within organisational networks. ISM-0635 is a specific, high-assurance segregation pattern for cross-domain solutions (directional path isolation), whereas Annex A 8.22 is broader and does not specifically mandate separate uplink/downlink paths.
Mappings show how controls relate across frameworks. They do not imply full equivalence or certification.