Write Blocker
A hardware device or software mechanism that permits read operations to a storage device while blocking all writes, so evidence cannot be altered during acquisition. It is used because simply attaching a disk to a running operating system is enough to modify it -- mounting can update access times, write recovery data or replay a journal. Hardware blockers are preferred for court-facing work; software blocking is common in field triage. Examined in GCFA, CHFI and CySA+ forensics domains.
Why It Matters
In practice the write blocker exists because the most common way to destroy evidence is not malice but a helpful operating system: plug an NTFS volume into a Windows box and it may update metadata and replay the journal before an analyst touches anything, and that single automatic write is enough for opposing counsel to argue the evidence was altered. Hardware blockers are favoured for defensibility because their behaviour is independent of the examining host's configuration, whereas a software approach depends on a setting that could be wrong or overridden. Whichever is used, practice is to verify the blocker actually blocked -- comparing hashes before and after attachment -- rather than trusting the label, and to record the make, model and firmware in the case notes. Note also that some interfaces and self-encrypting drives require particular handling. On exams such as GCFA and CHFI, expect questions on why mounting evidence read-only is not equivalent, and where a write blocker sits in the acquisition chain.
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Test your knowledge of Write Blocker concepts with exam-style practice questions.
Related Forensics terms
Digital Forensics
The scientific examination, collection, preservation, and analysis of digital evidence from computers, networks, mobile devices, and cloud environments for use in legal proceedings, incident response, or investigations. The forensic process follows strict procedures: identification, preservation (maintaining chain of custody), collection (creating forensic images), examination, analysis, and reporting. Key principles include working from forensic copies (never the original), documenting every action, and maintaining evidence integrity through cryptographic hashing. Tools include EnCase, FTK, Autopsy, and Volatility. Digital forensics is the focus of CHFI, GCFA, and GNFA certifications and is covered in CISSP Domain 7.
Chain of Custody
The documented and unbroken process of maintaining and controlling evidence to preserve its integrity and admissibility from the moment of collection through presentation in court. Every person who handles the evidence must be documented with dates, times, actions taken, and the reason for access. Any gap or irregularity in the chain of custody can cause evidence to be deemed inadmissible. In digital forensics, chain of custody includes hash verification at each transfer point, write-blocking during acquisition, and tamper-evident storage. This concept is critical for forensic examiners and is tested in CHFI, GCFA, and CISSP Domain 7 certifications.
Volatile Memory
Computer memory (RAM) that loses its contents when power is removed, making it a time-critical source of forensic evidence that must be captured before a system is shut down. Volatile memory contains running processes, open network connections, encryption keys, clipboard contents, logged-in users, and malware that may exist only in memory (fileless malware). Memory acquisition tools include FTK Imager, WinPmem, and LiME (Linux Memory Extractor), while analysis is performed with Volatility Framework or Rekall. The order of volatility (RFC 3227) dictates that RAM should be captured before disk, network, or other evidence. Memory forensics is a key skill in GCFA, CHFI, and incident response certifications.
Log Analysis
The examination of system, application, network, and security logs to identify security events, anomalies, policy violations, or evidence of attacks. Logs are generated by operating systems, firewalls, web servers, authentication systems, databases, and cloud services. Effective log analysis involves centralization (forwarding logs to a SIEM), normalization (standardizing formats), correlation (linking related events across sources), and alerting on suspicious patterns. Key log sources include Windows Event Logs, syslog, Apache/Nginx access logs, and cloud audit trails (AWS CloudTrail, Azure Activity Log). Log analysis is a core skill for SOC analysts and is tested in CySA+, CISSP, and GCIH certifications.
Memory Forensics
The forensic analysis of volatile memory (RAM) to extract evidence of malware, network connections, running processes, encryption keys, and other artifacts that may not be preserved on disk. Memory analysis can reveal malware that exists only in memory, decrypt encrypted volumes using keys in memory, and recover recently accessed data. Tools like Volatility, Rekall, and commercial memory analysis platforms enable automated analysis of memory dumps. Memory forensics is particularly valuable for analyzing advanced malware and rootkits that hide from traditional disk-based analysis.
Order of Volatility
The principle that digital evidence must be collected from most to least perishable, because acquiring one source can destroy another. The conventional order runs CPU registers and cache, then RAM, then network state and running processes, then temporary files, then disk, then remote logging and archival media. It governs live acquisition decisions in incident response and is examined in GCFA, GNFA, CHFI and CySA+ forensics domains.