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ASD ISMISM-1290

ASD ISM 1290 Controlled unpacking of archive files for filtering

What it says

Archive files are unpacked in a controlled manner to ensure content filter performance or availability is not adversely affected.

Quoted as published. Everything else on this page is written by Control Stack.

What it means

In plain English

Ensure unpacked archive files do not disrupt system filters or cause unavailability.

This control is about making sure that when you open archive files, like zip files, on your computer systems, nothing from inside causes problems. If you don't handle these properly, your system's security filters might miss harmful content, leading to viruses or malware infiltrating your systems, potentially shutting down operations.

Why it matters

Uncontrolled archive unpacking can cause filter bypass or resource exhaustion (e.g., archive bombs), degrading content filter performance/availability and disrupting operations.

How to implement

  1. IT team should ensure that archive files are unpacked in a quarantined area: Set up a specific computer or an isolated part of your network where archive files can be opened without affecting the rest of the system.

    It ensures that potentially dangerous files are detected and dealt with before they interact with your primary systems.

  2. System administrators should verify system filter configurations: Check that your content filtering systems are updated to handle newly unpacked files effectively.

    This might involve regular system updates and testing with sample archive files to see how the filters react.

  3. Managers should establish a clear policy on handling archive files: Develop guidelines that tell employees what to do if they have to open archive files.

    This might involve limited access to who can unpack these files and using specialised software that performs security checks.

  4. Training coordinators should organise regular training sessions: Educate staff on the risks of improperly unpacking archive files and how to use company-approved systems and processes.

    Keep these sessions practical with scenarios and examples they might encounter in their daily work.

  5. Procurement should work with IT to purchase and maintain approved software: Ensure that the organisation only uses tools that handle archive files safely and are vetted by cyber security experts.

    This keeps proprietary data safe and reduces the risk of introducing malicious software.

Keep it running

Enforce controlled unpacking limits (nesting depth, file count and total size) and regularly test with content filters to prevent archive bombs and performance degradation.

Evidence and audit

  1. Check 1 of 5What an auditor asks for

    Ask for

    The quarantine area setup documentation: Request proof of the specific system or network area used for safe file unpacking.

    Look at

    How this setup prevents files from impacting other system areas.

    Good evidence

    A document showing a physically or virtually isolated environment with access logs and successful test results.

  2. Check 2 of 5What an auditor asks for

    Ask for

    To see content filter reports: Request logs from content filtering systems after archives are unpacked.

    Look at

    Timestamps, file types, and any alerts triggered.

    Good evidence

    Logs showing that unpacking processes are flagged and managed without disrupting services.

  3. Check 3 of 5What an auditor asks for

    Ask for

    The policy documentation on handling archive files: Request the formal policy that outlines procedures for staff when dealing with archive files.

    Look at

    Clarity, accessibility, and comprehensive coverage of potential risks.

    Good evidence

    A dated document endorsed by management showing clear steps and staff responsibilities.

  4. Check 4 of 5What an auditor asks for

    Ask for

    Training records: Request records of staff training related to handling archive files securely.

    Look at

    Session dates, attendee lists, and training materials.

    Good evidence

    Recent training records with high attendance and updated content reflecting current best practices.

  5. Check 5 of 5What an auditor asks for

    Ask for

    Software procurement and licence agreements: Request documentation showing what software has been acquired for handling archive files.

    Look at

    Vendor security certifications and update records.

    Good evidence

    Valid licences for recommended software with recent security updates and vendor support assurance.

Mappings

Closest match in ISO/IEC 27001: A.8.7, Protection against malware, which this control depends on.

ISO 27001

ISO/IEC 27001: 1 mapping

Mappings show how controls relate across frameworks. They do not imply full equivalence or certification.