--- name: investigating-phishing-email-incident-fac65db8762e description: 'Investigates phishing email incidents from initial user report through header analysis, URL/attachment detonation, impacted user identification, and containment actions using SOC tools like Splunk, Microsoft Defender, and sandbox analysis platforms. Use when a reported phishing email requires full incident investigation to determine scope and impact. ' domain: cybersecurity subdomain: soc-operations tags: - soc - phishing - incident-response - email-security - splunk - defender - sandbox mitre_attack: - T1566.001 - T1566.002 - T1204.001 - T1598.003 version: '1.0' author: Krishna Kumar (xalgord) license: Apache-2.0 nist_csf: - DE.CM-01 - DE.AE-02 - RS.MA-01 - DE.AE-06 --- # Investigating Phishing Email Incident ## When to Use Use this skill when: - A user reports a suspicious email via the phishing report button or helpdesk ticket - Email security gateway flags a message that bypassed initial filters - Automated detection identifies credential harvesting URLs or malicious attachments - A phishing campaign targeting the organization requires scope assessment **Do not use** for spam or marketing emails without malicious intent — route those to email administration for filter tuning. ## Detection Gaps & Validation - **Clean attachment, weaponized link:** triagers detonate the attachment, get a benign verdict, and close — missing that the body's credential-harvest URL is the real payload. Always extract and analyze every URL (including those inside PDFs, QR codes, and HTML attachments) even when the file sandboxes clean. - **Delayed/cloaked payloads:** the URL serves a benign page to sandboxes and the harvester only after a redirect, on a second visit, or when the geo/User-Agent matches the target. Re-scan from a realistic egress and follow the full redirect chain rather than trusting a single URLScan result. - **SPF/DKIM "pass" ≠ legitimate:** a `dmarc=pass` from a lookalike or freshly registered domain, or a compromised-but-authenticated internal mailbox (thread hijacking), still phishes. Check domain age, display-name spoofing, and `Reply-To`/`Return-Path` mismatch, not just auth results. - **Scope undercounted:** searching only the reported subject misses recipients who got the same campaign with a rotated subject/sender. Pivot on sending IP, URL domain, and message-body hash, and confirm "who clicked" with proxy POSTs (credentials submitted) — not just GETs. - **Validate the verdict:** confirm a true positive by matching submitted-credential POSTs or sandbox C2 callbacks to the IOC, then audit each impacted mailbox for attacker-created inbox forwarding rules before declaring "no lateral movement". Tune FPs by routing confirmed marketing/bulk senders to gateway filtering instead of incident queues. ## Prerequisites - Access to email gateway logs (Proofpoint, Mimecast, or Microsoft Defender for Office 365) - Splunk or SIEM with email log ingestion (O365 Message Trace, Exchange tracking logs) - Sandbox access (Any.Run, Joe Sandbox, or Hybrid Analysis) for URL/attachment detonation - Microsoft Graph API or Exchange Admin Center for email search and purge operations - URLScan.io and VirusTotal API keys ## Workflow ### Step 1: Extract and Analyze Email Headers Obtain the full email headers (`.eml` file) from the reported message: ```python import email from email import policy with open("phishing_sample.eml", "rb") as f: msg = email.message_from_binary_file(f, policy=policy.default) # Extract key headers print(f"From: {msg['From']}") print(f"Return-Path: {msg['Return-Path']}") print(f"Reply-To: {msg['Reply-To']}") print(f"Subject: {msg['Subject']}") print(f"Message-ID: {msg['Message-ID']}") print(f"X-Originating-IP: {msg['X-Originating-IP']}") # Parse Received headers (bottom-up for true origin) for header in reversed(msg.get_all('Received', [])): print(f"Received: {header[:120]}") # Check authentication results print(f"Authentication-Results: {msg['Authentication-Results']}") print(f"DKIM-Signature: {msg.get('DKIM-Signature', 'NONE')[:80]}") ``` Key checks: - **SPF**: Does `Return-Path` domain match sending IP? Look for `spf=pass` or `spf=fail` - **DKIM**: Is the signature valid? `dkim=pass` confirms the email was not modified in transit - **DMARC**: Does the `From` domain align with SPF/DKIM domains? `dmarc=fail` indicates spoofing ### Step 2: Analyze URLs and Attachments **URL Analysis:** ```python import requests # Submit URL to URLScan.io url_to_scan = "https://evil-login.example.com/office365" response = requests.post( "https://urlscan.io/api/v1/scan/", headers={"API-Key": "YOUR_KEY", "Content-Type": "application/json"}, json={"url": url_to_scan, "visibility": "unlisted"} ) scan_id = response.json()["uuid"] print(f"Scan URL: https://urlscan.io/result/{scan_id}/") # Check VirusTotal for URL reputation import vt client = vt.Client("YOUR_VT_API_KEY") url_id = vt.url_id(url_to_scan) url_obj = client.get_object(f"/urls/{url_id}") print(f"VT Score: {url_obj.last_analysis_stats}") client.close() ``` **Attachment Analysis:** ```python import hashlib # Calculate file hashes with open("attachment.docx", "rb") as f: content = f.read() md5 = hashlib.md5(content).hexdigest() sha256 = hashlib.sha256(content).hexdigest() print(f"MD5: {md5}") print(f"SHA256: {sha256}") # Submit to MalwareBazaar for lookup response = requests.post( "https://mb-api.abuse.ch/api/v1/", data={"query": "get_info", "hash": sha256} ) print(response.json()["query_status"]) ``` Submit to sandbox (Any.Run or Joe Sandbox) for dynamic analysis of macros, PowerShell execution, and C2 callbacks. ### Step 3: Determine Campaign Scope Search for all recipients of the same phishing email in Splunk: ```spl index=email sourcetype="o365:messageTrace" (SenderAddress="attacker@evil-domain.com" OR Subject="Urgent: Password Reset Required" OR MessageId="") earliest=-7d | stats count by RecipientAddress, DeliveryStatus, MessageTraceId | sort - count ``` Alternatively, use Microsoft Graph API: ```python import requests headers = {"Authorization": f"Bearer {access_token}"} params = { "$filter": f"subject eq 'Urgent: Password Reset Required' and " f"receivedDateTime ge 2024-03-14T00:00:00Z", "$select": "sender,toRecipients,subject,receivedDateTime", "$top": 100 } response = requests.get( "https://graph.microsoft.com/v1.0/users/admin@company.com/messages", headers=headers, params=params ) messages = response.json()["value"] print(f"Found {len(messages)} matching messages") ``` ### Step 4: Identify Impacted Users (Who Clicked) Check proxy/web logs for users who visited the phishing URL: ```spl index=proxy dest="evil-login.example.com" earliest=-7d | stats count, values(action) AS actions, latest(_time) AS last_access by src_ip, user | lookup asset_lookup_by_cidr ip AS src_ip OUTPUT owner, category | sort - count | table user, src_ip, owner, actions, count, last_access ``` Check if credentials were submitted (POST requests to phishing domain): ```spl index=proxy dest="evil-login.example.com" http_method=POST earliest=-7d | stats count by src_ip, user, url, status ``` ### Step 5: Containment Actions **Purge emails from all mailboxes:** ```powershell # Microsoft 365 Compliance Search and Purge New-ComplianceSearch -Name "Phishing_Purge_2024_0315" ` -ExchangeLocation All ` -ContentMatchQuery '(From:attacker@evil-domain.com) AND (Subject:"Urgent: Password Reset Required")' Start-ComplianceSearch -Identity "Phishing_Purge_2024_0315" # After search completes, execute purge New-ComplianceSearchAction -SearchName "Phishing_Purge_2024_0315" -Purge -PurgeType SoftDelete ``` **Block indicators:** - Add sender domain to email gateway block list - Add phishing URL domain to web proxy block list - Add attachment hash to endpoint detection block list - Create DNS sinkhole entry for phishing domain **Reset compromised credentials:** ```powershell # Force password reset for impacted users $impactedUsers = @("user1@company.com", "user2@company.com") foreach ($user in $impactedUsers) { Set-MsolUserPassword -UserPrincipalName $user -ForceChangePassword $true Revoke-AzureADUserAllRefreshToken -ObjectId (Get-AzureADUser -ObjectId $user).ObjectId } ``` ### Step 6: Document and Report Create incident report with full timeline, IOCs, impacted users, and remediation actions taken. ```spl | makeresults | eval incident_id="PHI-2024-0315", reported_time="2024-03-15 09:12:00", sender="attacker@evil-domain[.]com", subject="Urgent: Password Reset Required", url="hxxps://evil-login[.]example[.]com/office365", recipients_count=47, clicked_count=5, credentials_submitted=2, emails_purged=47, passwords_reset=2, domains_blocked=1, disposition="True Positive - Credential Phishing Campaign" | table incident_id, reported_time, sender, subject, url, recipients_count, clicked_count, credentials_submitted, emails_purged, passwords_reset, disposition ``` ## Key Concepts | Term | Definition | |------|-----------| | **SPF (Sender Policy Framework)** | DNS TXT record specifying which mail servers are authorized to send on behalf of a domain | | **DKIM** | DomainKeys Identified Mail — cryptographic signature proving email content was not altered in transit | | **DMARC** | Domain-based Message Authentication, Reporting and Conformance — policy combining SPF and DKIM alignment | | **Credential Harvesting** | Phishing technique using fake login pages to capture username/password combinations | | **Business Email Compromise (BEC)** | Social engineering attack using compromised or spoofed executive email for financial fraud | | **Message Trace** | O365/Exchange log showing email routing, delivery status, and filtering actions for forensic analysis | ## Tools & Systems - **Microsoft Defender for Office 365**: Email security platform with Safe Links, Safe Attachments, and Threat Explorer for investigation - **URLScan.io**: Free URL analysis service capturing screenshots, DOM, cookies, and network requests - **Any.Run**: Interactive sandbox for detonating malicious files and URLs with real-time behavior analysis - **Proofpoint TAP**: Targeted Attack Protection dashboard showing clicked URLs and delivered threats per user - **PhishTool**: Dedicated phishing email analysis platform automating header parsing and IOC extraction ## Common Scenarios - **Credential Phishing**: Fake O365 login page — check proxy for POST requests, force password resets for submitters - **Macro-Enabled Document**: Word doc with VBA macro — sandbox shows PowerShell download cradle, check endpoints for execution - **QR Code Phishing (Quishing)**: Email contains QR code linking to credential harvester — decode QR, submit URL to sandbox - **Thread Hijacking**: Attacker uses compromised mailbox to reply in existing threads — check for impossible travel or new inbox rules - **Voicemail Phishing**: Fake voicemail notification with HTML attachment — analyze attachment for redirect chains ## Output Format ``` PHISHING INCIDENT REPORT — PHI-2024-0315 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Reported: 2024-03-15 09:12 UTC by jsmith (Finance) Sender: attacker@evil-domain[.]com (SPF: FAIL, DKIM: NONE, DMARC: FAIL) Subject: Urgent: Password Reset Required Payload: Credential harvesting URL IOCs: URL: hxxps://evil-login[.]example[.]com/office365 Domain: evil-login[.]example[.]com (registered 2024-03-14, Namecheap) IP: 185.234.xx.xx (VT: 12/90 malicious) Scope: Recipients: 47 users across Finance and HR departments Clicked: 5 users visited phishing URL Submitted: 2 users entered credentials (confirmed via POST in proxy logs) Containment: [DONE] 47 emails purged via Compliance Search [DONE] Domain blocked on proxy and DNS sinkhole [DONE] 2 user passwords reset, sessions revoked [DONE] MFA enforced for both compromised accounts [DONE] Inbox rules audited — no forwarding rules found Status: RESOLVED — No evidence of lateral movement post-compromise ``` --- Source attribution: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/soc-operations/investigating-phishing-email-incident/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/soc-operations/investigating-phishing-email-incident/SKILL.md Attribution basis: Source repository record Fields of work: Data & Analytics, Development & Engineering, Sales, Customer Support Roles: Customer Success Manager, Data Analyst, Security Engineer, Support Agent Specialties: API Tools: Hybrid Analysis, Joe Sandbox, Virustotal, Urlscan.Io, Any.Run Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 8206777ed400955c74de662b728c06589b8f62236c797d20c189eb5978f1317d