--- name: performing-file-carving-with-foremost-46fef094bbf4 description: Recover files from disk images and unallocated space using Foremost's header-footer signature carving to extract evidence regardless of file system state. domain: cybersecurity subdomain: digital-forensics tags: - forensics - file-carving - foremost - data-recovery - evidence-recovery - unallocated-space version: '1.0' author: Krishna Kumar (xalgord) license: Apache-2.0 nist_csf: - RS.AN-01 - RS.AN-03 - DE.AE-02 - RS.MA-01 --- # Performing File Carving with Foremost ## When to Use - When recovering files from unallocated disk space or corrupted file systems - For extracting evidence from formatted or wiped storage media - When file system metadata is unavailable but raw data sectors contain evidence - During investigations requiring recovery of specific file types from raw images - As a complement to file system-based recovery for maximum evidence extraction ## Detection Gaps & Validation - **Fragmentation is the #1 carving failure.** Header-footer carving assumes contiguous data; a file split across non-adjacent clusters is recovered truncated or stitched with unrelated sectors. Foremost/Scalpel do **not** reassemble fragments — corrupt output here is expected, not a tool error. Cross-check size/validity before trusting a carve. - **No footer = guesswork.** Types without a reliable footer (and `max_size` caps in `foremost.conf`/`scalpel.conf`) cause truncation or runaway over-reads. Tune `max_size` per type and verify the tail of large carves. - **Signature-only blind spots:** encrypted or compressed payloads have no plaintext magic bytes and will not carve; embedded files (e.g., a ZIP inside a `docx`, both `\x50\x4b\x03\x04`) get double-counted, inflating hit counts. - **False positives:** random data matching `\xff\xd8\xff`/`%PDF` produces files that pass the signature but fail to open. Validate with `file`, then actually parse/open (pdftotext, image render, `sqlite3 .schema`) before cataloging as evidence. - **Carving yields no filesystem context.** Carved files have **no original name, path, or `$STANDARD_INFORMATION` timestamps** — never assert when/where a carved artifact lived without a second source. - **Validate / cross-corroborate:** hash carved output (SHA-256) against NSRL (filter known-good) and known-bad sets, and reconcile against `$MFT`/file-system metadata, `bulk_extractor` features, and PhotoRec results to recover names/timestamps and confirm the recovery is genuine rather than a signature artifact. ## Prerequisites - Foremost installed on forensic workstation - Forensic disk image in raw (dd) format - Sufficient output storage (potentially larger than source) - Custom foremost.conf for specialized file types (optional) - Understanding of file signatures (magic bytes) for target file types - Scalpel as an alternative for performance-critical carving ## Workflow ### Step 1: Install and Configure Foremost ```bash # Install Foremost sudo apt-get install foremost # Verify installation foremost -V # Review default configuration cat /etc/foremost.conf # The default foremost.conf supports: # jpg, gif, png, bmp - Image formats # avi, exe, mpg, wav - Media and executables # riff, wmv, mov, pdf - Documents and video # ole (doc/xls/ppt), zip, rar - Office and archives # htm, cpp, java - Text/code files # Create custom configuration for additional file types cp /etc/foremost.conf /cases/case-2024-001/custom_foremost.conf # Add custom file signatures cat << 'EOF' >> /cases/case-2024-001/custom_foremost.conf # Custom additions for investigation # Format: extension case_sensitive max_size header footer docx y 10000000 \x50\x4b\x03\x04 \x50\x4b\x05\x06 xlsx y 10000000 \x50\x4b\x03\x04 \x50\x4b\x05\x06 pptx y 10000000 \x50\x4b\x03\x04 \x50\x4b\x05\x06 sqlite y 50000000 \x53\x51\x4c\x69\x74\x65\x20\x66\x6f\x72\x6d\x61\x74 pst y 500000000 \x21\x42\x44\x4e eml y 1000000 \x46\x72\x6f\x6d\x3a \x0d\x0a\x0d\x0a evtx y 50000000 \x45\x6c\x66\x46\x69\x6c\x65 EOF ``` ### Step 2: Run Foremost Against the Disk Image ```bash # Basic carving of all supported file types foremost -t all \ -i /cases/case-2024-001/images/evidence.dd \ -o /cases/case-2024-001/carved/foremost_all/ # Carve only specific file types foremost -t jpg,png,pdf,doc,xls,zip \ -i /cases/case-2024-001/images/evidence.dd \ -o /cases/case-2024-001/carved/foremost_targeted/ # Use custom configuration foremost -c /cases/case-2024-001/custom_foremost.conf \ -i /cases/case-2024-001/images/evidence.dd \ -o /cases/case-2024-001/carved/foremost_custom/ # Carve from a specific partition offset # First, find partitions mmls /cases/case-2024-001/images/evidence.dd # Then carve from unallocated space only # Extract unallocated space with blkls blkls -o 2048 /cases/case-2024-001/images/evidence.dd \ > /cases/case-2024-001/unallocated.dd foremost -t all \ -i /cases/case-2024-001/unallocated.dd \ -o /cases/case-2024-001/carved/foremost_unalloc/ # Verbose mode for detailed progress foremost -v -t all \ -i /cases/case-2024-001/images/evidence.dd \ -o /cases/case-2024-001/carved/foremost_verbose/ 2>&1 | \ tee /cases/case-2024-001/carved/foremost_log.txt # Indirect mode (process standard input) dd if=/cases/case-2024-001/images/evidence.dd bs=512 skip=2048 | \ foremost -t jpg,pdf -o /cases/case-2024-001/carved/foremost_pipe/ ``` ### Step 3: Use Scalpel for High-Performance Carving ```bash # Install Scalpel (faster alternative based on Foremost) sudo apt-get install scalpel # Edit Scalpel configuration (uncomment desired file types) cp /etc/scalpel/scalpel.conf /cases/case-2024-001/scalpel.conf # Uncomment lines for target file types in the config # Run Scalpel scalpel -c /cases/case-2024-001/scalpel.conf \ -o /cases/case-2024-001/carved/scalpel/ \ /cases/case-2024-001/images/evidence.dd # Scalpel with file size limits # Edit scalpel.conf to set appropriate max sizes: # jpg y 5000000 \xff\xd8\xff \xff\xd9 # pdf y 20000000 %PDF %%EOF ``` ### Step 4: Process and Validate Carved Files ```bash # Review Foremost audit report cat /cases/case-2024-001/carved/foremost_all/audit.txt # The audit.txt contains: # - Number of files found per type # - Start and end offsets # - File sizes # Validate carved files python3 << 'PYEOF' import os import subprocess from collections import defaultdict carved_dir = '/cases/case-2024-001/carved/foremost_all/' stats = defaultdict(lambda: {'total': 0, 'valid': 0, 'invalid': 0, 'size': 0}) for subdir in os.listdir(carved_dir): subdir_path = os.path.join(carved_dir, subdir) if not os.path.isdir(subdir_path) or subdir == 'audit.txt': continue for filename in os.listdir(subdir_path): filepath = os.path.join(subdir_path, filename) if not os.path.isfile(filepath): continue ext = subdir filesize = os.path.getsize(filepath) stats[ext]['total'] += 1 stats[ext]['size'] += filesize # Validate file using 'file' command result = subprocess.run(['file', '--brief', filepath], capture_output=True, text=True) file_type = result.stdout.strip() if 'data' in file_type.lower() or 'empty' in file_type.lower(): stats[ext]['invalid'] += 1 else: stats[ext]['valid'] += 1 print("=== CARVED FILE VALIDATION ===\n") print(f"{'Type':<10} {'Total':<8} {'Valid':<8} {'Invalid':<10} {'Total Size':<15}") print("-" * 55) for ext in sorted(stats.keys()): s = stats[ext] size_mb = s['size'] / (1024*1024) print(f"{ext:<10} {s['total']:<8} {s['valid']:<8} {s['invalid']:<10} {size_mb:>10.1f} MB") # Remove zero-byte files for subdir in os.listdir(carved_dir): subdir_path = os.path.join(carved_dir, subdir) if os.path.isdir(subdir_path): for filename in os.listdir(subdir_path): filepath = os.path.join(subdir_path, filename) if os.path.isfile(filepath) and os.path.getsize(filepath) == 0: os.remove(filepath) PYEOF # Hash all valid carved files find /cases/case-2024-001/carved/foremost_all/ -type f ! -name "audit.txt" \ -exec sha256sum {} \; > /cases/case-2024-001/carved/carved_file_hashes.txt # Check against known-bad hash database # Check against NSRL known-good database to filter ``` ### Step 5: Examine and Catalog Evidence Files ```bash # Extract metadata from carved images (EXIF data including GPS) exiftool -r -csv /cases/case-2024-001/carved/foremost_all/jpg/ \ > /cases/case-2024-001/analysis/carved_image_metadata.csv # Search carved documents for keywords find /cases/case-2024-001/carved/foremost_all/pdf/ -name "*.pdf" -exec pdftotext {} - \; 2>/dev/null | \ grep -iE '(confidential|secret|password|account|ssn|credit.card)' \ > /cases/case-2024-001/analysis/keyword_hits_pdf.txt # Generate thumbnails for image review mkdir -p /cases/case-2024-001/carved/thumbnails/ find /cases/case-2024-001/carved/foremost_all/jpg/ -name "*.jpg" -exec \ convert {} -thumbnail 200x200 /cases/case-2024-001/carved/thumbnails/{} \; 2>/dev/null # Create evidence catalog python3 << 'PYEOF' import os, hashlib, csv, subprocess catalog = [] carved_dir = '/cases/case-2024-001/carved/foremost_all/' for subdir in sorted(os.listdir(carved_dir)): subdir_path = os.path.join(carved_dir, subdir) if not os.path.isdir(subdir_path): continue for filename in sorted(os.listdir(subdir_path)): filepath = os.path.join(subdir_path, filename) if not os.path.isfile(filepath): continue size = os.path.getsize(filepath) sha256 = hashlib.sha256(open(filepath, 'rb').read()).hexdigest() file_type = subprocess.run(['file', '--brief', filepath], capture_output=True, text=True).stdout.strip() catalog.append({ 'filename': filename, 'type': subdir, 'size': size, 'sha256': sha256, 'file_description': file_type[:100] }) with open('/cases/case-2024-001/analysis/carved_file_catalog.csv', 'w', newline='') as f: writer = csv.DictWriter(f, fieldnames=['filename', 'type', 'size', 'sha256', 'file_description']) writer.writeheader() writer.writerows(catalog) print(f"Catalog created with {len(catalog)} files") PYEOF ``` ## Key Concepts | Concept | Description | |---------|-------------| | File carving | Recovering files by searching for known header/footer byte sequences in raw data | | File signature | Unique byte pattern at the start (header) or end (footer) identifying a file type | | Unallocated space | Disk sectors not assigned to any file; primary target for carving | | Fragmentation | When file data is stored in non-contiguous sectors, complicating carving | | Header-footer carving | Extracting data between known file start and end signatures | | False positives | Carved data matching file signatures but containing corrupt or unrelated content | | Slack space | Unused bytes at the end of a file's last allocated cluster | | Sector alignment | Files typically start at sector boundaries, improving carving accuracy | ## Tools & Systems | Tool | Purpose | |------|---------| | Foremost | Original header-footer file carving tool developed for US Air Force OSI | | Scalpel | High-performance file carver with configurable signatures | | PhotoRec | Signature-based file recovery supporting 300+ formats | | bulk_extractor | Extracts features (emails, URLs, credit cards) from raw data | | blkls | Sleuth Kit tool extracting unallocated space from disk images | | mmls | Partition table display for identifying carving targets | | ExifTool | Metadata extraction from carved image and document files | | hashdeep | Recursive hash computation for carved file cataloging | ## Common Scenarios **Scenario 1: Recovering Deleted Evidence Documents** Run Foremost targeting doc, pdf, xlsx formats against the unallocated space extracted with blkls, validate carved documents, search content for case-relevant keywords, catalog and hash all recoverable documents, present as evidence. **Scenario 2: Image Recovery from Formatted Media** Carve JPEG, PNG, GIF, BMP from a formatted USB drive image, extract EXIF metadata including GPS coordinates and camera information, generate thumbnails for rapid visual review, identify evidence-relevant images, document recovery chain. **Scenario 3: Email Recovery from Damaged PST** Use custom foremost.conf with PST and EML signatures, carve email artifacts from damaged Outlook data file, attempt to open carved PST fragments in a viewer, extract individual EML messages, search for relevant communications. **Scenario 4: Database Recovery for Financial Investigation** Configure Foremost to carve SQLite databases from unallocated space, recover application databases that were deleted, query recovered databases for financial records, cross-reference with known transaction data, document findings for prosecution. ## Output Format ``` File Carving Summary: Tool: Foremost 1.5.7 Source: evidence.dd (500 GB) Target: Unallocated space (234 GB) Duration: 1h 45m Files Carved: jpg: 2,345 files (1.8 GB) - Valid: 2,100 / Invalid: 245 png: 234 files (456 MB) - Valid: 210 / Invalid: 24 pdf: 156 files (890 MB) - Valid: 134 / Invalid: 22 doc: 89 files (234 MB) - Valid: 67 / Invalid: 22 xls: 45 files (123 MB) - Valid: 38 / Invalid: 7 zip: 67 files (567 MB) - Valid: 52 / Invalid: 15 exe: 34 files (234 MB) - Valid: 30 / Invalid: 4 sqlite: 12 files (89 MB) - Valid: 10 / Invalid: 2 Total Files: 2,982 (3.4 GB recovered) Evidence-Relevant: 45 files flagged for review Audit Log: /cases/case-2024-001/carved/foremost_all/audit.txt File Catalog: /cases/case-2024-001/analysis/carved_file_catalog.csv ``` --- Source attribution: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/digital-forensics/performing-file-carving-with-foremost/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. 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See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/digital-forensics/performing-file-carving-with-foremost/SKILL.md Attribution basis: Source repository record Fields of work: Data & Analytics Roles: Data Analyst Specialties: Specialty not specified Tools: Foremost Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 47917c37fc03ccde0d126b8261942762d39f96997ea9e673d6e695c80e9623f2