Audit logging integrity

Audit Logging Integrity

Overview

This skill ensures audit logs are generated, protected, retained, and reviewable per:

• HIPAA §164.312(b): Audit controls—hardware, software, procedural mechanisms to record and examine activity in systems containing ePHI
• SOC 2 CC7.2/CC7.3: System monitoring, anomaly detection, security event analysis
• PCI-DSS Req 10: Log and monitor all access to network resources and cardholder data

AI agents and MCP servers must emit structured, tamper-evident audit events without logging raw ePHI/CHD in cleartext.

When to Use

Use this skill when:

• Designing agent session audit trails (prompt metadata, tool calls, redaction counts)
• Validating MCP server logging (tool invocations, auth events)
• Integrating logs with SIEM (Splunk, Elastic, Datadog, Sentinel)
• Testing log integrity (append-only, WORM, hash chains)
• Preparing PCI Req 10 or HIPAA audit control evidence
• Investigating gaps in security event review (daily log review, alerting)

Do not use this skill when:

• Identity access certification (use access-control-identity-audit)
• Breach customer notification letters (use breach-incident-response)
• Initial SOC 2 TSC mapping (use soc2-trust-services-criteria)

Core Process

Execute steps in order.

Step 1: Audit event inventory

1. List all systems requiring audit logs:
   • Agent runtime, MCP servers, IdP, cloud control plane, CDE/ePHI databases
   • Evidence store, deanonymization tool invocations
2. Define required events per system:

System	Required events
Agent	session_start, session_end, skill_loaded, tool_called, redaction_count
MCP	oauth_token_issued, tool_invoke, auth_failure, config_change
IdP	login_success, login_failure, mfa_challenge, account_lockout
DB	query (metadata only), connection, privilege_change

3. Artifact: audit-event-catalog-{id}.json.

Step 2: Log content standards

1. Each event must include minimum fields:
   • timestamp_utc, event_id, actor_id, action, resource, result, source_ip, correlation_id
2. Prohibited in logs (or require field-level encryption):
   • Raw ePHI, PAN, CVV, secrets, full prompts with PHI
3. Acceptable alternatives:
   • Redacted prompt hash, token counts, resource IDs without patient identifiers
4. Verify agent logs entity_count from redaction, not original values.

Step 3: Tamper evidence

1. Implement one or more:
   • Append-only log storage (S3 Object Lock, immutability flags)
   • Hash chaining per log batch (prev_hash in each entry)
   • WORM SIEM index with retention lock
2. Restrict log deletion to break-glass role with dual control and post-use review.
3. Test: attempt delete/modify historical log as standard admin → must fail or generate alert.

Step 4: Centralization and SIEM integration

1. Forward all cataloged sources to SIEM within 24 hours (PCI Req 10.3).
2. Normalize to common schema (ECS, CEF, or OCSF).
3. Configure parsers for agent/MCP JSON logs.
4. Verify clock synchronization (NTP) across sources—PCI Req 10.4.

Step 5: Monitoring and review (CC7.3, PCI 10.6)

1. Daily automated review of security events (failed auth spikes, new MCP tools, deanonymize calls).
2. Alert thresholds documented with runbooks.
3. Sample weekly manual review with analyst sign-off for evidence.
4. Cross-link alerts to breach-incident-response playbooks.

Step 6: Retention and availability

1. Define retention per regulation and policy:
   • HIPAA: often 6 years for relevant documentation (org policy governs)
   • PCI Req 10.5: 12 months minimum, 3 months immediately available
   • SOC 2: examination period plus auditor request window
2. Test log search performance for incident queries across retention window.

Step 7: Agent/MCP forensic readiness

1. Verify correlation_id propagates: user session → agent run → MCP tool calls.
2. Test forensic reconstruction without raw PHI:
   • "Who invoked deanonymize_response at T?" → actor_id, justification ticket
3. Ensure MCP servers log authorization decision (allow/deny) per tool call.

Step 8: Gap analysis and remediation

1. Map gaps to §164.312(b), CC7.x, Req 10.x.
2. Prioritize: missing deanonymize audit = CRITICAL; delayed SIEM ingest = HIGH.
3. Package test results and sample log exports (redacted) for evidence.

Common Rationalizations

Excuse the agent might generate	Required rebuttal
"We log full prompts for debugging."	Full prompts with ePHI in logs violate minimum necessary and create secondary PHI store—log metadata only.
"Application logs on disk are enough."	Disk logs without tamper protection fail integrity requirements—implement append-only or SIEM immutability.
"MCP is stateless, no logging needed."	MCP tool calls accessing ePHI/CDE are audit-relevant events under HIPAA and PCI.
"Weekly log review is sufficient."	PCI requires daily security log review (10.6.1)—SOC 2 CC7 expects systematic monitoring.
"Deanonymization is internal—no audit trail."	Re-identification of PHI is high-risk—mandatory logged with actor and authorization.
"SIEM ingestion delay is acceptable."	PCI 10.3 requires timely centralization—>24h delay is a finding.

Red Flags

• Deanonymize tool invocations not logged
• MCP auth failures not forwarded to SIEM
• Logs contain cleartext SSN, PAN, or clinical notes
• Standard admin can delete production SIEM indices
• Agent sessions lack correlation_id across tool calls
• No daily security log review process or evidence
• Clock skew >5 minutes between agent and SIEM timestamps

Verification

• Audit event catalog complete for agent, MCP, IdP, and data systems
• Log field standards enforced—no raw ePHI/CHD in sample exports
• Tamper-evidence mechanism tested (modify/delete attempt fails or alerts)
• All sources forwarding to SIEM within PCI 24-hour requirement
• NTP/clock sync verified across logging infrastructure
• Daily automated security review configured with alert runbooks
• Retention policy documented and technically enforced (Object Lock/WORM)
• Correlation_id forensic test successfully traces session to MCP tools
• Deanonymization and privileged tool calls appear in audit samples
• Gap remediation plan mapped to HIPAA, SOC 2, and PCI requirements