Performing Cloud Storage Forensic Acquisition

Performing Cloud Storage Forensic Acquisition

Overview

Cloud storage forensic acquisition involves collecting digital evidence from services like Google Drive, OneDrive, Dropbox, and Box through both API-based remote acquisition and local endpoint artifact analysis. Modern investigations must address the challenge that cloud-synced files may exist in multiple states: locally synchronized, cloud-only (on-demand), cached, and deleted. Endpoint devices that have synchronized with cloud storage contain a wealth of metadata about locally synced files, files present only in the cloud, and even deleted items recoverable from cache folders. API-based acquisition using service-specific APIs provides direct access to remote data with valid credentials and proper legal authorization.

When to Use

• When conducting security assessments that involve performing cloud storage forensic acquisition
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Detection Gaps & Validation

• API acquisition captures current state, not history. Items purged past retention are gone — Google Drive Trash and OneDrive recycle bin typically hold ~30 days (OneDrive site/second-stage up to 93), Dropbox version history varies by tier. A clean recyclebin/Trash listing does not mean nothing was deleted; note the retention window as a coverage limit.
• Cloud-only files are absent on the endpoint. On-demand/"Files On-Demand" placeholders (OneDrive .cloud, DriveFS) are not stored locally, so disk imaging alone misses them — you need the API or the sync metadata DB.
• Encrypted/opaque local stores: Dropbox filecache.dbx/config.dbx are obfuscated SQLite and need decryption; parsing them raw yields nothing. OneDrive SyncEngineDatabase/<account>.dat schemas change across client versions.
• Anti-forensics seen in the wild: deleting individual file revisions (the worked example shows a malicious macro added then reverted) and unsharing links to hide exfil recipients.
• Timezone: API metadata (createdTime, modifiedTime) and revision times are UTC ISO-8601 — convert before merging with endpoint local times.
• Validate / cross-corroborate: verify each acquired file's API md5Checksum against the downloaded/hashed copy for chain of custody, and reconcile API metadata with endpoint sync logs, browser history (web uploads), and $MFT. Confirm external-sharing events against the provider admin/audit log, not just the file's permission list.

Prerequisites

• Legal authorization (warrant, consent, or corporate policy) for cloud data access
• Valid user credentials or administrative access tokens
• Magnet AXIOM Cloud, Cellebrite Cloud Analyzer, or equivalent tool
• KAPE with cloud storage target files
• Python 3.8+ with google-api-python-client, msal, dropbox SDK
• Network connectivity for API-based acquisition

Acquisition Methods

Method 1: API-Based Remote Acquisition

Google Drive API Acquisition

from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
from googleapiclient.http import MediaIoBaseDownload
import io
import os
import json
from datetime import datetime


class GoogleDriveForensicAcquisition:
    """Forensically acquire files and metadata from Google Drive via API."""

    def __init__(self, credentials_path: str, output_dir: str):
        self.creds = Credentials.from_authorized_user_file(credentials_path)
        self.service = build("drive", "v3", credentials=self.creds)
        self.output_dir = output_dir
        os.makedirs(output_dir, exist_ok=True)
        self.acquisition_log = []

    def list_all_files(self, include_trashed: bool = True) -> list:
        """List all files including trashed items."""
        files = []
        page_token = None
        query = "" if include_trashed else "trashed = false"

        while True:
            results = self.service.files().list(
                q=query,
                pageSize=1000,
                fields="nextPageToken, files(id, name, mimeType, size, "
                       "createdTime, modifiedTime, trashed, trashedTime, "
                       "owners, sharingUser, permissions, md5Checksum, "
                       "parents, webViewLink, driveId)",
                pageToken=page_token
            ).execute()

            files.extend(results.get("files", []))
            page_token = results.get("nextPageToken")
            if not page_token:
                break

        return files

    def download_file(self, file_id: str, file_name: str, mime_type: str) -> str:
        """Download a file from Google Drive preserving forensic integrity."""
        output_path = os.path.join(self.output_dir, file_name)

        if mime_type.startswith("application/vnd.google-apps"):
            export_formats = {
                "application/vnd.google-apps.document": "application/pdf",
                "application/vnd.google-apps.spreadsheet": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
                "application/vnd.google-apps.presentation": "application/pdf",
            }
            export_mime = export_formats.get(mime_type, "application/pdf")
            request = self.service.files().export_media(fileId=file_id, mimeType=export_mime)
        else:
            request = self.service.files().get_media(fileId=file_id)

        with io.FileIO(output_path, "wb") as fh:
            downloader = MediaIoBaseDownload(fh, request)
            done = False
            while not done:
                _, done = downloader.next_chunk()

        self.acquisition_log.append({
            "timestamp": datetime.utcnow().isoformat(),
            "file_id": file_id,
            "file_name": file_name,
            "output_path": output_path,
            "action": "downloaded"
        })
        return output_path

    def get_activity_log(self, file_id: str) -> list:
        """Retrieve activity/revision history for a specific file."""
        revisions = self.service.revisions().list(
            fileId=file_id,
            fields="revisions(id, modifiedTime, lastModifyingUser, size, md5Checksum)"
        ).execute()
        return revisions.get("revisions", [])

    def export_acquisition_report(self) -> str:
        """Export acquisition log for chain of custody documentation."""
        report_path = os.path.join(self.output_dir, "acquisition_log.json")
        with open(report_path, "w") as f:
            json.dump({
                "acquisition_start": self.acquisition_log[0]["timestamp"] if self.acquisition_log else None,
                "acquisition_end": datetime.utcnow().isoformat(),
                "total_files": len(self.acquisition_log),
                "entries": self.acquisition_log
            }, f, indent=2)
        return report_path

OneDrive / Microsoft 365 API Acquisition

import msal
import requests
import os
import json
from datetime import datetime


class OneDriveForensicAcquisition:
    """Forensically acquire files and metadata from OneDrive via Microsoft Graph API."""

    def __init__(self, client_id: str, tenant_id: str, client_secret: str, output_dir: str):
        self.output_dir = output_dir
        os.makedirs(output_dir, exist_ok=True)

        authority = f"https://login.microsoftonline.com/{tenant_id}"
        self.app = msal.ConfidentialClientApplication(
            client_id, authority=authority, client_credential=client_secret
        )
        token_result = self.app.acquire_token_for_client(
            scopes=["https://graph.microsoft.com/.default"]
        )
        self.access_token = token_result.get("access_token")
        self.headers = {"Authorization": f"Bearer {self.access_token}"}
        self.base_url = "https://graph.microsoft.com/v1.0"

    def list_user_files(self, user_id: str) -> list:
        """List all files in user's OneDrive."""
        url = f"{self.base_url}/users/{user_id}/drive/root/children"
        files = []
        while url:
            response = requests.get(url, headers=self.headers)
            data = response.json()
            files.extend(data.get("value", []))
            url = data.get("@odata.nextLink")
        return files

    def download_file(self, user_id: str, item_id: str, filename: str) -> str:
        """Download a file from OneDrive."""
        url = f"{self.base_url}/users/{user_id}/drive/items/{item_id}/content"
        response = requests.get(url, headers=self.headers, stream=True)
        output_path = os.path.join(self.output_dir, filename)
        with open(output_path, "wb") as f:
            for chunk in response.iter_content(chunk_size=8192):
                f.write(chunk)
        return output_path

    def get_deleted_items(self, user_id: str) -> list:
        """Retrieve items from OneDrive recycle bin."""
        url = f"{self.base_url}/users/{user_id}/drive/special/recyclebin/children"
        response = requests.get(url, headers=self.headers)
        return response.json().get("value", [])

Method 2: Local Endpoint Artifact Collection

KAPE Targets for Cloud Storage

# Collect all cloud storage artifacts using KAPE
kape.exe --tsource C: --tdest C:\Output\CloudArtifacts --target GoogleDrive,OneDrive,Dropbox,Box

# OneDrive artifacts
# %USERPROFILE%\AppData\Local\Microsoft\OneDrive\logs\
# %USERPROFILE%\AppData\Local\Microsoft\OneDrive\settings\
# %USERPROFILE%\OneDrive\

# Google Drive artifacts
# %USERPROFILE%\AppData\Local\Google\DriveFS\
# Contains metadata SQLite databases and cached files

# Dropbox artifacts
# %USERPROFILE%\AppData\Local\Dropbox\
# %USERPROFILE%\Dropbox\.dropbox.cache\
# Contains filecache.dbx (encrypted SQLite), host.dbx, config.dbx

OneDrive Local Database Analysis

import sqlite3
import os

def analyze_onedrive_sync_engine(db_path: str) -> list:
    """Analyze OneDrive SyncEngineDatabase for file metadata."""
    conn = sqlite3.connect(db_path)
    cursor = conn.cursor()

    # Query for all tracked files including cloud-only items
    cursor.execute("""
        SELECT fileName, fileSize, lastChange,
               resourceID, parentResourceID, eTag
        FROM od_ClientFile_Records
        ORDER BY lastChange DESC
    """)

    files = []
    for row in cursor.fetchall():
        files.append({
            "filename": row[0],
            "size": row[1],
            "last_change": row[2],
            "resource_id": row[3],
            "parent_id": row[4],
            "etag": row[5]
        })

    conn.close()
    return files

Cloud Storage Artifacts Summary

References

• SANS Cloud Storage Acquisition: https://www.sans.org/blog/cloud-storage-acquisition-from-endpoint-devices
• Magnet AXIOM Cloud: https://www.magnetforensics.com/blog/how-to-acquire-and-analyze-cloud-data-with-magnet-axiom/
• AWS Cloud Forensics Framework: https://docs.aws.amazon.com/prescriptive-guidance/latest/security-reference-architecture/cyber-forensics.html
• API-Based Forensic Acquisition of Cloud Drives: https://arxiv.org/abs/1603.06542

Example Output

$ python3 cloud_forensic_acquire.py --provider google-drive --auth /tokens/gdrive_token.json \
    --user jsmith@corporate.com --output /acquisition/gdrive

Cloud Storage Forensic Acquisition Tool v3.2
==============================================
Provider:    Google Drive
Account:     jsmith@corporate.com
Start Time:  2024-01-19 08:00:15 UTC
Auth Method: Admin SDK (domain-wide delegation)

[+] Enumerating files...
    Total files:        2,345
    Total folders:      178
    Shared with me:     456
    Trashed items:      89 (included in acquisition)
    Total size:         14.7 GB

[+] Acquiring file contents...
    Downloaded:    2,345 / 2,345  [████████████████████████████████] 100%
    Errors:        0
    Elapsed:       18m 32s

[+] Acquiring metadata...
    File metadata:      2,345 entries
    Revision history:   8,912 revisions across 1,234 files
    Sharing permissions: 3,456 permission entries
    Activity log:       12,345 events

[+] Acquiring trashed items...
    Recovered:     89 / 89 items (234 MB)

--- Acquisition Log ---
Timestamp (UTC)          | Action           | File                                    | Size    | SHA-256
2024-01-19 08:00:45      | Downloaded       | /My Drive/Finance/Q4_Report.xlsm        | 245 KB  | 7a3b8c9d...
2024-01-19 08:00:46      | Downloaded       | /My Drive/Finance/Budget_2024.xlsx       | 1.2 MB  | 8b4c9d0e...
...
2024-01-19 08:02:12      | Trash-Recovered  | /Trash/employee_list_full.csv            | 4.5 MB  | 9c5d0e1f...
2024-01-19 08:02:13      | Trash-Recovered  | /Trash/network_diagram_v3.vsdx          | 2.1 MB  | 0d6e1f2a...
2024-01-19 08:02:14      | Trash-Recovered  | /Trash/credentials_backup.kdbx          | 128 KB  | 1e7f2a3b...

--- Sharing Analysis ---
Files Shared Externally:
  /My Drive/Finance/Q4_Report.xlsm     → j.smith.personal8842@protonmail.com (2024-01-16 03:10 UTC)
  /My Drive/HR/employee_list_full.csv   → j.smith.personal8842@protonmail.com (2024-01-16 03:12 UTC)
  /My Drive/IT/network_diagram_v3.vsdx  → anonymous (link sharing, 2024-01-16 03:15 UTC)

--- Revision History (Suspicious) ---
File: /My Drive/Finance/Q4_Report.xlsm
  Rev 1:  2024-01-10 09:00:00 UTC  (245 KB)  - Original
  Rev 2:  2024-01-15 14:35:00 UTC  (248 KB)  - Modified (macro added)
  Rev 3:  2024-01-16 03:05:00 UTC  (245 KB)  - Reverted (macro removed - anti-forensics)

Acquisition Summary:
  Files acquired:       2,345 (14.7 GB)
  Trashed items:        89 (234 MB)
  Revisions:            8,912
  Chain of custody hash (full archive):
    SHA-256: a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2
  Output directory:     /acquisition/gdrive/
  Acquisition log:      /acquisition/gdrive/acquisition_log.csv
  Completion Time:      2024-01-19 08:18:47 UTC