File Integrity Monitoring for Logs

“File integrity monitoring for logs” is a practical requirement with a narrow goal: stop attackers (or insiders) from quietly editing audit logs after the fact. In PCI DSS 4.0.1 Requirement 10.3.4, the test is simple: if someone changes existing audit log data, your control must detect it and generate an alert. (PCI DSS v4.0.1 Requirement 10.3.4)

For a Compliance Officer, CCO, or GRC lead, operationalizing this quickly means translating a single sentence into an implementable control: define which audit logs are in scope, deploy FIM/change-detection on those logs (or on immutable log stores where “change” is structurally prevented), route alerts to the right responders, and retain evidence that proves the control is continuously active. The work is less about writing a policy and more about engineering the “tamper-evidence” property into your logging pipeline.

This page gives requirement-level guidance you can hand to Security Engineering and your SIEM/SOC team, plus the audit artifacts you should pre-package for your next PCI assessment.

Regulatory text

Requirement statement (excerpt): “File integrity monitoring or change-detection mechanisms is used on audit logs to ensure that existing log data cannot be changed without generating alerts.” (PCI DSS v4.0.1 Requirement 10.3.4)

Operator interpretation: what you must do

• Identify the audit logs that support PCI security monitoring and investigations.
• Implement FIM or equivalent change-detection on those audit logs (or on the log storage layer where log records are written).
• Configure the mechanism so that any change to existing log data generates an alert.
• Be able to demonstrate coverage, configuration, and working alerting in the cardholder data environment (CDE) and connected systems where audit logs are relevant. (PCI DSS v4.0.1 Requirement 10.3.4)

Plain-English requirement (what the assessor is trying to confirm)

Your environment must make it hard to rewrite history. If an attacker gains admin access, one of their first moves is to delete or edit logs to hide lateral movement, data access, and persistence. This requirement forces you to implement controls that either:

• detect modification of log files/records after they are written, or
• make logs effectively immutable, with alerting on any attempted or actual change.

The “gotcha” is scope: many teams have FIM on operating system files, but not on the audit logs themselves. PCI DSS 10.3.4 is explicitly about audit logs. (PCI DSS v4.0.1 Requirement 10.3.4)

Who it applies to

Entity types

• Merchants, service providers, and payment processors that must meet PCI DSS. (PCI DSS v4.0.1 Requirement 10.3.4)

Operational contexts where this becomes real work

• You store logs locally on servers (classic /var/log/* patterns) and ship them later.
• You centralize logs into a SIEM but still keep local copies.
• You use managed platforms (cloud services, containers) where “log files” may be abstracted, so you need change-detection on the storage layer or the centralized log system.
• You rely on third parties to host systems in scope; you still need evidence that the control exists and that alerts are generated and handled.

What you actually need to do (step-by-step)

1) Define “audit logs” in scope and map where they live

Create an inventory that answers:

• Which systems generate audit logs relevant to PCI monitoring?
• Where are those logs stored after generation (local disk, centralized store, object storage, managed service)?
• Who has permissions to read, write, delete, and administer the log path or log store?

Deliverable: a scoped list of log sources and storage locations that engineering and auditors can both understand.

2) Choose the technical approach: file-based FIM vs. storage-level immutability

Two common patterns can meet the intent of the requirement, if implemented with alerting:

A. Host-based FIM on log files

• Deploy an agent that hashes/monitors log files and triggers alerts on changes to existing content.
• Confirm it detects edits, truncation, deletion, and permission changes where applicable.
• Ensure it is active on every in-scope host or log collector path.

B. Centralized, append-only / immutable logging with change detection

• If logs are written into a system that prevents modification of existing records, the “change” condition shifts to attempted tampering (administrative actions, retention changes, bucket policy edits, deletion attempts).
• You still need alerts when existing log data would be affected.

Decision rule you can use internally: if you cannot confidently explain “what happens when someone edits yesterday’s log,” you do not have a passable design for 10.3.4. (PCI DSS v4.0.1 Requirement 10.3.4)

3) Engineer alerting that is actionable (not just “enabled”)

The requirement demands that changes generate alerts. Make that provable:

• Define alert conditions: modification, truncation, deletion, permission/ownership change on log files; administrative actions affecting stored logs.
• Route alerts to a monitored queue (SIEM/SOC, ticketing, on-call).
• Set severity guidance (at least internally) for “log tampering suspected.”

Operational note: auditors often ask who receives alerts and what they do next. Have a short runbook.

4) Reduce bypass paths

Attackers try to disable the detector before editing logs. Focus on:

• Limiting who can stop/disable the FIM agent or tamper with its config.
• Monitoring changes to the FIM configuration itself.
• Segregating duties: log admins should not be the only people who can silence alerts.
• Ensuring the FIM system forwards alerts off-host quickly so an attacker cannot erase the evidence locally.

5) Test the control with a repeatable “tamper test”

Build a simple test procedure you can run on demand (for audits and after major changes):

• Pick a representative in-scope system.
• Modify an existing log file entry (or simulate a change in the log store that affects existing data).
• Confirm an alert is generated, received, and tracked to closure.

Keep the test evidence. This is one of the fastest ways to end assessor debate because it shows the control working. (PCI DSS v4.0.1 Requirement 10.3.4)

6) Operationalize ownership and escalation

Assign:

• Control owner (often Security Operations or Platform Security).
• Responder for alerts (SOC/on-call).
• Evidence owner (GRC or control owner).

If you use a third party SOC, make sure the contract and process cover log-tamper alerts and ticket evidence retention.

7) Package audit-ready evidence continuously

Do not wait for the ROC/SAQ cycle. Build an “evidence folder” that you refresh after major logging changes.

If you use Daydream to manage control ownership and evidence collection, map this requirement to a single control record with: system scope, FIM configuration snapshots, alert samples, and the tamper-test packet so you are not rebuilding the story during the assessment.

Required evidence and artifacts to retain

Keep artifacts that prove four things: scope, configuration, alerting, and operations.

Scope and design

• Log source inventory and where each log is stored.
• Data flow diagram (even lightweight) showing generation → storage → monitoring.

Configuration evidence

• Screenshots/exports of FIM or change-detection configuration showing monitored paths or monitored log stores.
• Agent deployment coverage report or host list that matches your scope.

Alerting and response

• Example alert records from a test or real event, showing timestamp, affected log object, and destination (SIEM/ticket).
• Runbook or SOP for log-tamper alerts, including escalation and investigation steps.

Ongoing operations

• Tickets/cases showing alert triage and closure notes.
• Change records for modifications to logging, log retention, or FIM configuration.

Common exam/audit questions and hangups

Expect assessors to probe these areas:

1. “Which audit logs are covered?”
   They want a scoped list tied to your CDE and supporting systems, not “all logs everywhere.”

2. “Show me an alert from a change to an existing log.”
   Have a tamper-test alert ready and explain how it was generated. (PCI DSS v4.0.1 Requirement 10.3.4)

3. “What stops an admin from editing logs and clearing the alert?”
   Be ready to explain off-host alerting, role restrictions, and monitoring of FIM disablement.

4. “Is this monitoring the logs, or the logging system binaries?”
   Many teams confuse OS FIM with log FIM. This requirement is log-focused. (PCI DSS v4.0.1 Requirement 10.3.4)

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails	Fix
FIM only on /etc, binaries, or registry	Doesn’t address “audit logs” explicitly	Add monitored log paths and validate alerting on edits (PCI DSS v4.0.1 Requirement 10.3.4)
Alerts exist but go nowhere	“Generating alerts” means someone receives and can act	Route to SIEM/ticket/on-call with documented ownership
Monitoring only detects file creation, not modification	Requirement is about changes to existing log data	Test edits/truncation/deletion and tune rules
Overbroad scope creates alert fatigue	Teams start ignoring alerts	Start with PCI-relevant audit logs and tune with change windows/runbooks
No retained evidence	Control may work, but you cannot prove it	Pre-package config exports and a tamper-test packet

Risk implications (why auditors care)

If audit logs can be edited without detection, you lose the ability to reconstruct incidents, prove what happened, and demonstrate control effectiveness. In payment environments, that translates to longer dwell time for attackers and weaker forensic outcomes. PCI DSS treats log integrity as a foundational security capability because every downstream detection and investigation depends on trustworthy logs. (PCI DSS v4.0.1 Requirement 10.3.4)

Practical 30/60/90-day execution plan

First 30 days (establish coverage and prove alerting)

• Confirm in-scope systems and audit log locations for the CDE and connected components.
• Select your approach (host FIM vs centralized immutability plus change detection) per log location.
• Implement monitoring on the highest-risk log stores first (domain/admin activity logs, security event logs, system logs on CDE hosts).
• Run and document a tamper test that produces an alert. (PCI DSS v4.0.1 Requirement 10.3.4)

By 60 days (make it operational, reduce bypass risk)

• Expand coverage to remaining in-scope log sources and collectors.
• Add monitoring for disablement/config changes of the FIM tool or logging pipeline components.
• Finalize runbooks: triage steps, escalation, and evidence capture expectations.
• Establish a standard evidence packet for audits (config exports + sample alerts + tickets).

By 90 days (stabilize, audit-package, and govern change)

• Tune alert thresholds and suppress known-good noise without weakening tamper detection.
• Add control checks to change management (new systems must include log integrity monitoring).
• Validate coverage routinely through spot checks and repeatable tamper tests.
• Centralize evidence tracking in your GRC workflow (Daydream can track control ownership and evidence refresh tasks so the control does not decay between assessments).

Frequently Asked Questions

Do we need file integrity monitoring on every log file on every system?

You need FIM or change-detection on audit logs in scope for PCI so that changes to existing log data generate alerts. Start from your CDE and connected systems, then expand based on where PCI-relevant audit trails are stored. (PCI DSS v4.0.1 Requirement 10.3.4)

If we ship logs to a SIEM, can we skip monitoring local log files?

Not automatically. If local logs remain and could be used for investigation, assessors often expect integrity protections there too, or a clear architectural rationale for relying on centralized, tamper-evident storage. Your evidence must show that changes to existing log data generate alerts. (PCI DSS v4.0.1 Requirement 10.3.4)

What exactly counts as “existing log data cannot be changed without generating alerts”?

Treat it as “after the log record is written, any edit, truncation, deletion, or manipulation that alters prior entries triggers an alert.” Prove it with a documented tamper test and an alert artifact. (PCI DSS v4.0.1 Requirement 10.3.4)

Are permission changes on log directories part of this requirement?

The text focuses on changes to existing log data, but permission/ownership changes are common precursors to tampering. Monitor them where feasible because they strengthen your ability to detect and investigate log integrity events. (PCI DSS v4.0.1 Requirement 10.3.4)

How do we show evidence to an assessor without dumping huge volumes of logs?

Provide a scoped system list, configuration exports showing monitored log paths/stores, and a small set of alert examples (including a tamper test) with associated tickets. The goal is to prove the mechanism works and is operational. (PCI DSS v4.0.1 Requirement 10.3.4)

We outsource parts of our CDE to a third party. Who is responsible for FIM on logs?

You remain responsible for PCI compliance outcomes. Contractually require the third party to operate change-detection on audit logs and to provide audit-ready evidence and alert/ticket records on request. (PCI DSS v4.0.1 Requirement 10.3.4)