Analyzing Office365 Audit Logs For Compromise

Analyzing Office 365 Audit Logs for Compromise

Overview

Business Email Compromise (BEC) attacks often leave traces in Office 365 audit logs: suspicious inbox rule creation, email forwarding to external addresses, mailbox delegation changes, and unauthorized OAuth application consent grants. This skill uses the Microsoft Graph API to query the Unified Audit Log, enumerate inbox rules across mailboxes, detect forwarding configurations, and identify compromised account indicators.

When to Use

Trigger phrases:

• "analyzing office365 audit logs for compromise"

• "Parse Office 365 Unified Audit Logs via Microsoft Graph API to detect email forw"

• When investigating security incidents that require analyzing office365 audit logs for compromise

• When building detection rules or threat hunting queries for this domain

• When SOC analysts need structured procedures for this analysis type

• When validating security monitoring coverage for related attack techniques

Prerequisites

• Azure AD app registration with AuditLog.Read.All, MailboxSettings.Read, Mail.Read (application permissions)
• Python 3.9+ with msal, requests
• Client secret or certificate for authentication
• Global Reader or Security Reader role

Steps

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}

1. Authenticate to Microsoft Graph using MSAL client credentials flow
2. Query Unified Audit Log for suspicious operations (Set-Mailbox, New-InboxRule)
3. Enumerate inbox rules across mailboxes and flag forwarding rules
4. Detect mailbox delegation changes (Add-MailboxPermission)
5. Identify OAuth consent grants to suspicious applications
6. Check for suspicious sign-in patterns from audit logs
7. Generate compromise indicator report with timeline

Expected Output

• JSON report listing forwarding rules, delegation changes, OAuth grants, and suspicious audit events with risk scores
• Timeline of compromise indicators with affected mailboxes

When NOT to Use

• You need to perform the attack, not analyze it (use performing-* skills)
• Task is about detection, not analysis (use detecting-* skills)
• You need to implement controls (use implementing-* skills)
• Task is about threat hunting, not post-incident analysis (use hunting-* skills)
• You don't have access to the artifacts/logs to analyze
• Task requires real-time monitoring (use SOC tools)

Red Flags

• Performing actions without explicit written authorization from the asset owner
• Testing against production systems without a defined scope and rules of engagement
• Treating compliance checklists as security guarantees rather than minimum baselines
• Failing to document exceptions and risk acceptance decisions
• Relying on point-in-time audits instead of continuous monitoring

Process

1. Scope — Define research questions, identify data sources, set time boundaries
2. Gather — Collect data from primary sources, APIs, and public records
3. Synthesize — Analyze findings, identify patterns, produce actionable report

Verification

• All steps executed successfully against a test environment before production use
• Output documented with screenshots or logs demonstrating expected behavior
• Vulnerabilities reproduced with proof-of-concept and impact analysis
• False positives filtered out through manual verification
• Fix recommendations include code-level remediation guidance

Anti-Rationalization Table