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investigating-phishing-email-incident 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.
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4 fichiers name investigating-phishing-email-incident 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 ["T1078","T1685.002","T1685.005","T1566","T1598"] version 1.0 author mahipal license Apache-2.0 nist_csf ["DE.CM-01","DE.AE-02","RS.MA-01","DE.AE-06"] source https://github.com/mukul975/Anthropic-Cybersecurity-Skills source_commit 04450304b12645cb2b974ab96d28c0664758a88d note Vendored verbatim from an external Apache-2.0 security-skill library, pinned by commit. Exceeds the internal 300-line skill guideline (agent-code-constraints.md) -- kept as-is because this is vendored reference material (forensics/threat-intel procedure), not Yana AI-authored content, and trimming would damage technical accuracy.
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.
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:
import email
from email import policy
with open ("phishing_sample.eml" , "rb" ) as f:
msg = email.message_from_binary_file(f, policy=policy.default)
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' ]} "
for
in
reversed
'Received'
print
f"Received: {header[:120 ]} "
print
f"Authentication-Results: {msg['Authentication-Results' ]} "
print
f"DKIM-Signature: {msg.get('DKIM-Signature' , 'NONE' )[:80 ]} "
SPF : Does Return-Path domain match sending IP? Look for spf=pass or spf=failDKIM : Is the signature valid? dkim=pass confirms the email was not modified in transitDMARC : Does the From domain align with SPF/DKIM domains? dmarc=fail indicates spoofing
Step 2: Analyze URLs and Attachments import requests
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} /" )
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()
import hashlib
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} " )
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:
index=email sourcetype="o365:messageTrace"
(SenderAddress="attacker@evil-domain.com" OR Subject="Urgent: Password Reset Required"
OR MessageId="<phishing-message-id@evil.com>")
earliest=-7d
| stats count by RecipientAddress, DeliveryStatus, MessageTraceId
| sort - count
Alternatively, use Microsoft Graph API:
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:
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):
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:
# 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
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:
# 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.
| 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 investigationURLScan.io : Free URL analysis service capturing screenshots, DOM, cookies, and network requestsAny.Run : Interactive sandbox for detonating malicious files and URLs with real-time behavior analysisProofpoint TAP : Targeted Attack Protection dashboard showing clicked URLs and delivered threats per userPhishTool : 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 submittersMacro-Enabled Document : Word doc with VBA macro — sandbox shows PowerShell download cradle, check endpoints for executionQR Code Phishing (Quishing) : Email contains QR code linking to credential harvester — decode QR, submit URL to sandboxThread Hijacking : Attacker uses compromised mailbox to reply in existing threads — check for impossible travel or new inbox rulesVoicemail 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
