Digital › Module 3 › Lesson 3
Write Blockers
Write blockers prevent accidental writes to source media — name hardware vs software blockers for YOUR $DFIR_LAB acquisition checklist.
Visual · t26_write_blockers
Write-blocker literacy. $DFIR_LAB only. Original Cyberlium.
Opening
One accidental write can destroy defense — blockers enforce read-only at the hardware or driver layer.
Hardware write blockers sit between source disk and workstation — USB, SATA, NVMe bridges certified for forensic use. Software write blockers mount images read-only or set registry/driver policies on live systems (use with extreme care and authority). Goal: examiner cannot alter source sectors during imaging. Cyberlium names blocker types on YOUR $DFIR_LAB checklist — practice images often skip physical hardware, but habit still documents 'read-only mount' for E01. Next: Acquisition Lab.
1. Hardware blockers (named)
Tableau, WiebeTech, and similar bridges — verify LED/status, firmware, and supported interface before casework. Chain blocker serial in CoC when org requires.
Lab students may only see photos/diagrams — still name the purpose: prevent writes to evidence drive.
Command guide
Try these commands — Hardware blockers (named)
═══ TOOLS & WEBSITES ═══ Browse / read these (authorized learning only — stay in YOUR lab / program scope)
Write blockers — https://www.sans.org/cyber-security-skills/digital-forensics/ (hardware write-block literacy) NIST CFReDS — https://www.nist.gov/itl/ssd/software-quality-group/computer-forensics-reference-data-sets-cfreds RFC 3227 — https://www.rfc-editor.org/rfc/rfc3227 (preserve original evidence)
═══ INSTALL ═══
Linux (Debian/Ubuntu):
Command — copy this
sudo apt install python3
macOS:
Command — copy this
brew install python3
Windows: Download https://python.org/downloads/
═══ LINUX / macOS ═══
Command — copy this
export LAB_DFIR=${LAB_DFIR:-$HOME/cyberlium-lab/t26-dfir}
cat > "$LAB_DFIR/notes/write-blocker-policy.txt" <<'EOF'
WRITE BLOCKER POLICY (lab literacy):
- work on COPIES under evidence/ — never alter originals in place
- refuse writes to evidence media without documented blocker/simulator
- lab: cp sample.bin to analysis/ before strings/hex edits
- NEVER: mount stranger production disk read-write
EOFCommand — copy this
grep -E 'refuse|COPIES|NEVER' "$LAB_DFIR/notes/write-blocker-policy.txt"
python3 -c "print('Integrity demo: hash BEFORE and AFTER copy — digests must match on unchanged copy')"Primary tools to practice this lesson: grep, python3. Reference sites: Write blockers (https://www.sans.org/cyber-security-skills/digital-forensics/); NIST CFReDS (https://www.nist.gov/itl/ssd/software-quality-group/computer-forensics-reference-data-sets-cfreds); RFC 3227 (https://www.rfc-editor.org/rfc/rfc3227). Run every command in the box — install first, then the usage lines — only on YOUR lab / program scope.
2. Software read-only mounts
Mount E01/raw read-only in Linux (ro loop), use examiner tools' read-only modes, disable auto-mount on forensic workstation. VM shared folders are NOT forensic blockers — know the difference.
On $DFIR_LAB, note how YOU mount practice images read-only in your lab VM.
3. Acquisition checklist tie-in
Forbidden: imaging a live stranger laptop without authority and without documented method. Allowed: acquisition checklist line — blocker type, verify read-only, hash source.
Ship: three-line acquisition safety checklist for $DFIR_LAB. Next: Acquisition Lab.
4. What you ship: write-blocker checklist for $DFIR_LAB
Hardware vs software blocker notes, read-only mount rule. $DFIR_LAB named. chmod 600.
5. What you record before the next lesson
Date. Blocker checklist. $DFIR_LAB named. File t26-m03-l03-write-blockers.txt chmod 600.
6. Wrong vs right: tampering evidence vs chain of custody
Worked failure — same MSF word, opposite target. Right never needs a café Wi-Fi or classmate laptop.
Wrong
Mount evidence read-write 'for speed.' Skip blocker documentation on physical cases.
Right
Write write-blocker checklist for YOUR $DFIR_LAB workflow. Next: Acquisition Lab.
Mission: document read-only habit
1) Contrast hardware vs software blockers. 2) State YOUR read-only mount method. 3) Add verify step before imaging. 4) chmod 600.
Stuck? Ask Cyberlium AI Mentor
Read-only mount beats apologizing for altered sectors.
Knowledge Check
APPLY: Write blockers primarily prevent:
Multiple choice
Knowledge Check
APPLY: True or False: Forensic workstations should mount evidence read-only when possible.
True or False
Knowledge Check
APPLY: Software read-only mounts require:
Multiple choice