SOC Analyst: Investigating a Compromised Mailbox

Why Investigate?

A compromised mailbox is a critical security incident that can lead to:

• Data Exfiltration: Attackers may steal sensitive data, such as customer information or proprietary documents.
• Phishing Campaigns: Compromised accounts can be used to send phishing emails, targeting internal or external recipients.
• Account Takeover: Attackers may escalate access to other systems or accounts within the organization.
• Business Disruption: Malicious activity can disrupt operations or lead to financial loss.
• Regulatory Non-Compliance: Breaches may violate standards like GDPR, PCI-DSS, or SOX, resulting in penalties.

As a SOC analyst, my priority is to quickly validate and contain the incident to limit impact, preserve evidence, and support the organization’s security posture.

Incident Response Process

My investigation follows the SOC’s incident response framework, aligned with NIST 800-61, and includes detection, analysis, containment, eradication, recovery, and post-incident activities.

1. Detection and Triage

Objective: Confirm the alert and prioritize the incident.

• Review Alert: Analyze the SIEM alert or user report (e.g., suspicious email or login) in tools like Splunk or Microsoft Sentinel.
• Validate Incident: Check for indicators like unusual login locations or unauthorized email activity.
• Assign Priority: Use the SOC’s severity matrix to prioritize based on impact and scope.
• Log Incident: Create a ticket in the SOC’s case management system (e.g., ServiceNow, Jira).

Why: Ensures the incident is legitimate and prioritized appropriately for rapid response.

2. Initial Analysis

Objective: Determine the scope and nature of the compromise.

• Check Login Activity: Review authentication logs for unfamiliar IPs, devices, or geolocations using Microsoft 365 audit logs or SIEM dashboards.
• Analyze Suspicious Emails: Inspect email headers, attachments, and URLs in a sandbox (e.g., Any.Run, JoeSandbox).
• Interview Reporter: If user-reported, gather details via secure communication channels.
• Correlate Events: Cross-reference with other alerts (e.g., failed logins, DLP triggers) to identify patterns.

Why: Confirms the compromise and identifies immediate risks to guide containment.

3. Detailed Investigation

Objective: Identify the root cause, attack vector, and full scope.

• Log Analysis:
  • Query email server logs for sent/deleted emails or forwarding rules.
  • Check Active Directory logs for credential misuse or privilege escalation.
  • Use SIEM tools to aggregate and correlate logs.
• Threat Intelligence: Compare indicators of compromise (IOCs) like IP addresses or domains with feeds (e.g., VirusTotal, AlienVault OTX).
• Credential Compromise:
  • Verify if credentials were leaked (e.g., HaveIBeenPwned).
  • Check for phishing emails or malware infections via EDR tools (e.g., CrowdStrike, Carbon Black).
• Lateral Movement: Investigate access to other systems (e.g., SharePoint, VPN) using network traffic analysis.

Why: Provides a comprehensive understanding of the incident to inform containment and remediation.

4. Containment

Objective: Stop the threat and limit further damage.

• Short-Term Actions:
  • Lock or suspend the compromised account.
  • Revoke active sessions and reset passwords.
  • Quarantine malicious emails using email security tools (e.g., Proofpoint, Mimecast).
• Long-Term Actions:
  • Block malicious IPs or domains via firewall rules.
  • Notify recipients of phishing emails to prevent further interaction.

Why: Halts the attack while preserving evidence for further analysis.

5. Eradication and Recovery

Objective: Remove the threat and restore normal operations.

• Eradicate: Remove malware, delete unauthorized rules, and clear compromised sessions.
• Strengthen Security: Enforce MFA, update email filtering policies, and patch vulnerabilities.
• Restore Access: Re-enable the account after verifying security controls.
• Monitor: Set up SIEM alerts for similar activity to detect recurrence.

Why: Ensures the threat is fully eliminated and systems are secure before resuming operations.

6. Post-Incident Activities

Objective: Document, report, and improve SOC processes.

• Document Findings: Update the incident ticket with a timeline, root cause, and actions taken.
• Escalate if Needed: Notify incident response leads or management for high-severity incidents.
• External Reporting: Inform regulators or affected parties if required (e.g., data breach notifications).
• Lessons Learned: Conduct a debrief to identify process gaps and update playbooks.

Why: Enhances SOC readiness and ensures compliance with organizational and regulatory requirements.

Tools and Processes

As a SOC analyst, I rely on a suite of tools and standardized processes to investigate efficiently:

• Tools:
  • SIEM: Splunk, Microsoft Sentinel, QRadar for log aggregation and alerting.
  • Email Security: Microsoft 365 Defender, Proofpoint, Mimecast for email analysis and quarantine.
  • EDR: CrowdStrike, Carbon Black for endpoint threat detection.
  • Threat Intelligence: VirusTotal, AlienVault OTX for IOC enrichment.
  • Sandbox: Any.Run, JoeSandbox for malware analysis.
  • Case Management: ServiceNow, Jira for incident tracking.
• Processes:
  • Follow SOC runbooks for mailbox compromise incidents.
  • Adhere to chain-of-custody for evidence handling.
  • Escalate incidents per the SOC’s escalation matrix.
  • Align with NIST 800-61 and organizational incident response policies.
• Collaboration:
  • Coordinate with IT for account management and system access.
  • Work with the incident response team for complex investigations.
  • Engage legal/compliance teams for regulatory reporting.

Additional Considerations

• Real-Time Monitoring: Continuously monitor SIEM and EDR alerts during the investigation.
• Shift Handoff: Document all actions clearly for the next SOC shift to ensure continuity.
• Communication: Use concise, actionable updates when reporting to stakeholders.
• Compliance: Ensure all actions comply with data protection and privacy regulations.

Summary

As a SOC analyst responding to a compromised mailbox alert, I would:

1. Triage the alert, validate the incident, and create a ticket.
2. Analyze login activity, emails, and correlated events to assess scope.
3. Investigate logs, IOCs, and potential lateral movement to identify the root cause.
4. Contain the incident by locking the account and quarantining emails.
5. Eradicate threats, restore secure access, and implement monitoring.
6. Document findings, escalate if needed, and conduct a lessons-learned review.

This process ensures rapid response, minimizes impact, and strengthens the organization’s security posture.