CyberGlossary

Forensics & IR

Write Blocker

Also known as: Forensic write blocker, Read-only bridge

Definition

A hardware or software tool that permits read access to a storage device while preventing any write operations that could alter evidence.

Write blockers are core to forensic evidence acquisition: they ensure the source disk, USB drive, or memory card remains bit-for-bit identical during imaging. Hardware blockers sit inline between the suspect drive and the examiner workstation (Tableau, WiebeTech, CRU), exposing read-only protocol interfaces and often interpreting SATA, NVMe, USB, SAS, or M.2 connections. Software blockers (such as Linux blockdev settings, USBWriteBlocker, or registry-controlled Windows policies) achieve similar protection on a workstation. NIST's Computer Forensics Tool Testing (CFTT) program publishes test results validating tool behaviour. Using a write blocker is required practice under ISO/IEC 27037 to preserve evidentiary integrity.

Examples

  • A Tableau T8u USB 3.0 hardware write blocker used while imaging a suspect external drive.
  • A Linux examination workstation configured with udev rules and blockdev to prevent accidental writes.

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