Conditional Access Policy Investigation - Instructions

Purpose

This skill investigates Conditional Access (CA) policy changes in correlation with sign-in failures to detect:

• Legitimate troubleshooting (authorized policy changes to resolve access issues)
• Security control bypass (unauthorized policy modifications to circumvent blocks)
• Privilege abuse (users with admin rights weakening security controls)

The key distinction is whether policy changes were authorized and necessary vs self-service bypass of security controls.

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📑 TABLE OF CONTENTS

1. Critical Investigation Rules - Mandatory workflow steps
2. Common Error Codes - Sign-in failure reference
3. CA Policy States - Understanding policy modes
4. 5-Step Investigation Workflow - KQL queries and analysis
5. Real-World Example - Complete walkthrough
6. Critical Mistakes - What NOT to do
7. Security Recommendations - Remediation guidance

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Critical Investigation Rules

When investigating sign-in failures (error codes 53000, 50074) with CA policy correlation:

⚠️ MANDATORY STEPS - DO NOT SKIP:

1. Query ALL CA policy changes in chronological order (±2 days from failure time)
2. Parse policy state transitions from the JSON (enabled → disabled → report-only)
3. Compare failure timeline with policy change timeline
4. Verify logical consistency: Ask "does this make sense?"

Key Questions to Answer:

• Was the user blocked BEFORE the policy change?
• Did the policy change resolve the block?
• Who initiated the policy change? (same user = suspicious)
• What was the business justification?

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Common Error Codes

Error Code	Description	Typical Cause
53000	Device not compliant	Device not enrolled in Intune or failing compliance checks
50074	Strong authentication required	MFA not satisfied
50074	User must enroll in MFA	MFA not configured for user
530032	Blocked by CA policy	Generic CA policy block
65001	User consent required	Application consent needed
53003	Access blocked by CA policy	Explicit block condition met
70044	Session expired	User needs to re-authenticate

Error Code Investigation Priority

Priority	Error Codes	Investigation Focus
HIGH	53000, 530032, 53003	Device compliance, CA policy blocks - check for policy manipulation
MEDIUM	50074	MFA requirements - check if MFA was bypassed
LOW	65001, 70044	Consent/session issues - usually not security-related

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CA Policy State Meanings

State	What It Means	Security Impact
enabled	Policy actively enforcing	Blocks non-compliant access (intended behavior)
disabled	Policy not enforcing	Security control bypassed - all access allowed
enabledForReportingButNotEnforced	Report-only mode	Logs violations but doesn't block - defeats purpose

State Transition Risk Assessment

Transition	Risk Level	Interpretation
enabled → disabled	HIGH	Complete security bypass
enabled → enabledForReportingButNotEnforced	MEDIUM-HIGH	Partial bypass (monitoring only)
disabled → enabled	LOW	Security restored (good)
enabledForReportingButNotEnforced → enabled	LOW	Security strengthened (good)

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Investigation Workflow Pattern

Step 1: Identify Sign-In Failures

Query sign-in failures with CA context:

// Get failures with CA context
union isfuzzy=true SigninLogs, AADNonInteractiveUserSignInLogs
| where TimeGenerated between (datetime(<START>) .. datetime(<END>))
| where UserPrincipalName =~ '<UPN>'
| where ResultType != '0'
| where AppDisplayName has '<APPLICATION>'  // e.g., "Visual Studio Code"
| project TimeGenerated, IPAddress, Location, ResultType, ResultDescription, 
    ConditionalAccessStatus, UserAgent
| order by TimeGenerated asc

What to Look For:

• ResultType values: 53000, 50074, 530032, 53003
• ConditionalAccessStatus: "failure", "notApplied"
• Pattern of repeated failures followed by success

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Step 2: Query ALL CA Policy Changes in Timeframe

CRITICAL: Query ±2 days from the first failure time

let failure_time = datetime(<FIRST_FAILURE_TIME>);
let start = failure_time - 2d;
let end = failure_time + 2d;
AuditLogs
| where TimeGenerated between (start .. end)
| where OperationName has_any ("Conditional Access", "policy")
| where Identity =~ '<UPN>' or tostring(InitiatedBy) has '<UPN>'
| extend InitiatorUPN = tostring(parse_json(InitiatedBy).user.userPrincipalName)
| extend InitiatorIPAddress = tostring(parse_json(InitiatedBy).user.ipAddress)
| extend TargetName = tostring(parse_json(TargetResources)[0].displayName)
| project TimeGenerated, OperationName, Result, InitiatorUPN, InitiatorIPAddress, 
    TargetName, CorrelationId
| order by TimeGenerated asc  // CRITICAL: Chronological order

Critical Analysis Points:

• InitiatorUPN: Who made the change? Same user as blocked = suspicious
• TargetName: Which policy was modified?
• TimeGenerated: Did change occur AFTER sign-in failures?
• Order: Always chronological (oldest first) to see cause/effect

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Step 3: Parse Policy State Changes

For each CorrelationId from Step 2, get detailed changes:

// Get detailed property changes for a specific policy modification
AuditLogs
| where CorrelationId == "<CORRELATION_ID>"
| extend ModifiedProperties = parse_json(TargetResources)[0].modifiedProperties
| mv-expand ModifiedProperties
| extend PropertyName = tostring(ModifiedProperties.displayName)
| extend OldValue = tostring(ModifiedProperties.oldValue)
| extend NewValue = tostring(ModifiedProperties.newValue)
| project TimeGenerated, PropertyName, OldValue, NewValue

Key Properties to Extract:

• Look for "state" property in the JSON
• Parse OldValue and NewValue for state transitions
• Document: enabled → disabled → enabledForReportingButNotEnforced

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Step 4: Extract Policy State from JSON

Manual JSON Parsing:

The OldValue and NewValue fields contain JSON. Look for the "state" field:

{
  "state": "enabled",
  "conditions": { ... },
  "grantControls": { ... }
}

Build the Timeline:

1. Extract "state" from each OldValue and NewValue
2. Create chronological list: enabled → disabled → enabledForReportingButNotEnforced
3. Correlate with sign-in failure timeline

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Step 5: Security Assessment

Compare timelines and assess intent:

Pattern	Interpretation	Risk Level
Failures → Policy Disabled	User bypassed security control to unblock self	HIGH - Privilege abuse
Failures → Policy Changed to Report-Only	User weakened security control	MEDIUM-HIGH - Partial bypass
Policy Disabled → Failures Continue	Cached tokens (5-15 min propagation delay)	INFO - Expected behavior
Policy Changed → No More Failures	Policy change resolved issue	Context-dependent - May be legitimate troubleshooting
Different user made change	Admin assisted with access issue	LOW - Likely legitimate (verify authorization)

Risk Escalation Criteria:

Criteria	Risk Level
Same user blocked AND made policy change	HIGH
Policy disabled within 30 minutes of first failure	HIGH
Multiple policies modified	HIGH
Change made outside business hours	MEDIUM-HIGH
No change request ticket/approval	MEDIUM-HIGH
Admin made change for blocked user (with ticket)	LOW

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Real-World Example Analysis

Scenario: User blocked by device compliance policy, then modifies policy

Timeline

Time	Event	Details
19:05	Sign-in failure	Error 53000: device not compliant
19:06	Sign-in failure	Error 53000: device not compliant
19:07	Sign-in failure	Error 53000: device not compliant
19:09	Policy change	enabled → disabled
19:09	Policy change	disabled → enabledForReportingButNotEnforced
19:12	Sign-in failure	Error 53000 (cached token)
19:14	Sign-in success	Access granted

Analysis

1. ✅ Policy was correctly blocking non-compliant device

   • Device compliance policy was enforcing as intended
   • User's device failed compliance checks (not enrolled or failing policy)

2. 🚨 User disabled security control to bypass block

   • Same user who was blocked made the policy change
   • Change occurred within 4 minutes of repeated failures
   • No approval or change request documented

3. ⚠️ User partially reversed by enabling report-only

   • Shows some awareness that disabling was too aggressive
   • But report-only still defeats the purpose (doesn't block)

4. ❌ Report-only mode is NOT a valid security posture

   • Logs violations but allows non-compliant access
   • Creates false sense of security (policy "exists" but doesn't protect)

Assessment

Field	Value
Risk Level	MEDIUM-HIGH
Finding	Self-service security bypass using privileged role
Root Cause	User's device is non-compliant (not enrolled/failing compliance)
Policy Impact	Device compliance checks now ineffective for all users

Recommendations

1. Immediate Actions:

   • Restore policy to enabled state
   • Verify user's device compliance status
   • Document incident for security review

2. User-Specific:

   • Enroll user's device in Intune
   • Verify device meets compliance requirements
   • Review if user needs Security Administrator role

3. Process Improvements:

   • Implement approval workflow for CA policy changes
   • Create alert for policy state changes (enabled → disabled/report-only)
   • Review all users with permission to modify CA policies
   • Consider PIM for Security Administrator role

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Critical Mistakes to Avoid

❌ DON'T:

Mistake	Why It's Wrong
Query only ONE policy change event	You'll miss the sequence of changes
Read policy changes in reverse chronological order	Confuses cause/effect relationship
Assume policy was already disabled	Must check starting state from OldValue
Skip verifying "does this make logical sense?"	Disabled policies can't block users
Ignore the initiator identity	Same user = suspicious, different admin = verify authorization
Focus only on final state	The transition sequence reveals intent

✅ DO:

Best Practice	Why It Matters
Query ALL policy changes in the timeframe	Complete picture of modifications
Order chronologically (oldest first)	See cause/effect sequence
Parse the full JSON for state transitions	Extract exact policy states
Cross-check: blocked user → policy must be enabled	Logical consistency verification
Ask: "Why would user disable this policy?"	Usually to bypass a legitimate block
Check if initiator had authorization	Ticket, approval, documented reason

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Security Recommendations

When CA Policy Changes Are Detected

1. Determine Legitimacy

• Was the policy change authorized?
• Was there a valid business reason?
• Did the user have approval to make this change?
• Is there a change request ticket?

2. Assess Impact

• How many users affected by policy change?
• What applications/resources are now unprotected?
• How long was the policy disabled/weakened?
• Are there compliance implications (regulatory requirements)?

3. Remediation Actions

Action	Priority
Restore policy to enabled state if unauthorized	IMMEDIATE
Investigate root cause (why was user blocked?)	HIGH
Fix underlying issue (device compliance, MFA enrollment)	HIGH
Review who has permission to modify CA policies	MEDIUM
Implement approval workflows for policy changes	MEDIUM
Create alerts for future CA policy modifications	MEDIUM

4. Long-Term Improvements

Improvement	Benefit
Use PIM for Security Administrator role	Requires approval for elevated access
Implement CA policy change alerts	Real-time notification of modifications
Require multi-admin approval for state changes	Prevents single-person bypass
Document approved procedures	Clear guidance for legitimate troubleshooting
Regular access reviews	Ensure only necessary users have CA admin rights

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Prerequisites

Required MCP Servers

This skill requires:

1. Microsoft Sentinel MCP - For KQL queries against SigninLogs and AuditLogs
   • mcp_sentinel-data_query_lake: Execute KQL queries
   • mcp_sentinel-data_search_tables: Discover table schemas

Required Data Sources

• SigninLogs - Interactive sign-in events with CA status
• AADNonInteractiveUserSignInLogs - Non-interactive sign-in events
• AuditLogs - CA policy modification events

Required Permissions

To view CA policy changes in AuditLogs, ensure:

• Sentinel workspace has AuditLogs ingestion enabled
• User has appropriate RBAC to query the workspace

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Integration with Other Skills

CA Policy Investigation often follows a user-investigation:

1. Run user-investigation skill → Identifies sign-in failures
2. Notice CA-related error codes → 53000, 50074, 530032
3. Run ca-policy-investigation skill → Correlate failures with policy changes
4. Document findings → Security assessment with remediation recommendations

Key Integration Points:

• Sign-in failure data comes from user investigation
• CA policy changes are NEW queries specific to this skill
• Assessment combines timeline correlation with policy state analysis