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 EnglishEnsure 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.
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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
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.
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.
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.
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.
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
- 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.
- 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.
- 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.
- 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.
- 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/IEC 27001: 1 mapping
This control depends on A.8.7.
ISM-1290 requires controlled unpacking of archive files to prevent malicious or pathological archives from reducing filter performance or causing unavailability. ISO/IEC 27001:2022 Annex A 8.7 requires organisations to implement protection against malware, and controlled unpacking strengthens malware protection by enabling safe inspection/scanning of archive contents while mitigating decompression-bomb denial-of-service risks. Annex A 8.7 is broader (all malware controls), whereas ISM-1290 is specifically about archive unpacking safeguards in the content filtering process.
Mappings show how controls relate across frameworks. They do not imply full equivalence or certification.




