Responding to AD security incidents in real time

Real-time mindset: speed with control

In an AD incident, you are always trading off three things: containment (stop ongoing abuse), continuity (keep business running), and confidence (know what truly happened). Real-time response works when you:

• Prefer reversible actions (disable, isolate, block, restrict) before destructive ones (wipe, reboot, mass reset).
• Preserve forensic signal (logs, volatile evidence, timeline) before making changes that erase it.
• Assume AD replication delay—your changes and the attacker’s changes both take time to converge.
• Protect the “control plane”: domain controllers, admin workstations, tier-0 accounts, PKI, identity sync.

If your environment is hybrid, treat on-prem AD and Entra ID as a single identity system. Attackers do. If you need a companion read on cloud-side monitoring, see How to monitor and report security events in Microsoft Entra ID.

Before the incident: the 3 things that decide your outcome

You can absolutely respond in real time without “perfect” prep—but your best outcomes come from three foundations:

1) Telemetry you can trust (and query fast)

• Centralized Windows Security logs from DCs + key servers (forwarded, stored, searchable).
• Identity detections mapped to AD semantics (abnormal LDAP, DC replication abuse signals, suspicious ticketing patterns).
• Endpoint telemetry on admin workstations and DCs (process creation, script block logging where possible, sign-in trails).

If you use Microsoft’s identity detection stack, ensure you’ve correctly configured event collection and coverage. Start here: Microsoft Defender for Identity: A comprehensive overview and Event collection with Microsoft Defender for Identity.

2) Privilege design that limits “instant domain admin” paths

Most AD “real-time disasters” happen because privilege is too easy to inherit: delegation sprawl, broad OU rights, overpowered service accounts, or legacy permissions nobody can explain. Two useful references for reducing this risk are: How to delegate OU permissions with minimal risk and Excess Permissions: Lessons from Legacy Setups.

3) A break-glass path that does not depend on compromised identity

• Known-good admin workstation or secured jump host with audited access.
• Break-glass accounts protected and monitored (preferably offline-stored credentials, strong MFA where applicable).
• Documented “who can do what” in the first hour (disable accounts, isolate hosts, block network paths, change GPO, etc.).

The first 15 minutes: stabilize and protect the evidence

The goal is to stop the bleeding enough to keep the attacker from escalating, while you preserve what you need to understand scope.

A. Declare a single incident channel and decision owner

• One incident commander (IC) to approve risky actions.
• One scribe to timestamp actions (this becomes your reconstruction timeline).
• One technical lead each for AD, endpoints, network, cloud identity (if hybrid).

B. Protect the control plane immediately

• Freeze privileged change windows: no “routine” AD/GPO modifications until cleared by IC.
• Quarantine admin access: stop using everyday workstations to administer AD.
• Move to known-good tooling: use a secured admin host (or jump box) for all changes.

C. Preserve key logs and snapshots

Before you start changing lots of objects, ensure you are not about to overwrite the only evidence you have. At minimum:

• Confirm DC Security logs are forwarding and retained.
• Export/backup relevant logs from critical systems if retention is short.
• Capture a list of current Domain Admins / Enterprise Admins / Schema Admins memberships (baseline for later diff).

D. Identify the “patient zero” starting point

Real-time response needs one anchor: a user, device, server, or alert that started the investigation. Write down:

• Suspected account(s) involved
• Suspected host(s) involved
• Approximate time window
• Primary symptom (lockouts, unusual admin group change, abnormal ticketing, suspicious replication, etc.)

The first hour: scope and contain without breaking AD

The first hour is where teams either (1) contain the attacker cleanly or (2) self-inflict an outage while the attacker adapts. Your objective is to limit privilege movement and stop new persistence.

Step 1: Determine the level of identity compromise

Ask (and answer with evidence): Are we dealing with a single user compromise, admin credential compromise, or DC-level compromise? The response differs dramatically.

• User-only compromise: suspicious sign-ins, MFA fatigue, impossible travel, one endpoint involved.
• Privileged compromise: admin group membership changes, service account abuse, abnormal admin logons.
• DC-level compromise: suspicious changes on DCs, directory replication misuse, log tampering, widespread ticket anomalies.

Step 2: Contain at the narrowest effective boundary

Containment should start narrow and expand only if evidence forces you to. Typical “narrow first” moves:

• Disable the single suspicious account (or reset credentials) if clearly malicious.
• Isolate the single suspicious workstation/server from the network.
• Block a suspicious source IP/VPN session or restrict admin logon paths temporarily.

Step 3: Diff privileged reality against expected reality

Attackers love silent privilege changes. In the first hour, do a quick audit of:

• Membership changes to privileged groups (Domain Admins, Enterprise Admins, Administrators, Account Operators, etc.).
• New accounts created or disabled accounts re-enabled.
• GPO edits or new GPO links, especially those that deploy scripts, scheduled tasks, or local admin additions.
• Changes to delegation / ACLs / AdminSDHolder-protected objects.

Step 4: Establish a “known-good admin identity” lane

If you cannot trust your admin accounts, your ability to respond collapses. Move to:

• Break-glass accounts (logged, justified usage) from a known-good admin host.
• Short-lived privileged elevation where available (JIT/JEA), with strict auditing.

High-signal AD indicators to check immediately

You do not need a perfect hunt to act in real time. You need a few high-signal checks that catch common “identity takeover” moves.

1) Authentication spikes and anomalies

• Unusual failed logon storms (4625) or lockouts (4740) centered on a service account or admin.
• Admin logons from unusual hosts, times, or protocols.
• Legacy auth usage spikes (e.g., NTLM/older patterns) where you expect Kerberos.

If lockouts or failed logons are your trigger, this reference helps you quickly track sources: Account Lockout Event ID: How to Find Account Lockouts. For understanding the auth mechanics behind what you see in logs, keep this handy: NTLM authentication and Kerberos Authentication Protocols Explained.

2) Privileged group membership changes

• Any additions to Domain Admins / Enterprise Admins / built-in Administrators.
• Any creation of “shadow” privileged groups and nesting them into privileged groups.
• Any changes to groups that control GPO management or local admin at scale.

3) Directory changes that represent persistence

• New user/computer objects created unexpectedly.
• Changes to delegation settings or ACLs on OUs, admin groups, or critical service accounts.
• GPOs modified to execute code (startup scripts, scheduled tasks, registry run keys, etc.).

4) Log tampering

• Security log cleared events, or sudden gaps in logs from DCs.
• Audit policy changes.
• Unusual service stop/start patterns on logging/EDR agents.

Containment actions: what to do (and what not to do)

Containment in AD is about preventing new privilege and new lateral movement, not instantly “fixing everything.” Use this order of operations: identity → endpoints → AD configuration → network.

Containment moves that are usually safe (reversible)

• Disable clearly compromised accounts (rather than deleting them).
• Reset credentials for suspicious accounts (prefer staged resets for service accounts to avoid outages).
• Isolate compromised endpoints/servers (quarantine VLAN or EDR isolation).
• Block suspicious inbound admin protocols to DCs from non-admin subnets (temporary firewall rules).
• Restrict where admins can log on (temporary “admin only from PAW/jump hosts” enforcement).

Containment moves that can backfire (do carefully)

• Mass password resets without a dependency map (services, scheduled tasks, apps may fail).
• Rebooting domain controllers early (can destroy volatile evidence and complicate timeline).
• Blindly reverting GPOs (might remove protections or break business-critical configs).
• Disabling replication without a plan (can fragment the directory and complicate recovery).

Decision point: do you suspect DC-level compromise?

If you have credible evidence that a domain controller is compromised, treat it as a “control plane breach.” Your priorities become:

• Prevent further privileged authentication from suspicious hosts.
• Validate integrity of privileged groups and high-value AD objects.
• Prepare for a structured recovery path (which may include rebuilding trust boundaries).

Practical containment “scripts” (conceptual)

The exact commands vary by environment; the important part is the intent: quickly list deltas and stop new abuse. Keep your changes minimal and auditable.

# Examples of what you want to answer quickly (conceptual)
# - Which privileged groups changed today?
# - Which accounts logged on to DCs in the last hour?
# - Which GPOs changed recently?
# - Which OUs had ACL/delegation changes?

Eradication: removing persistence safely

Once containment is holding, eradication is the work of removing attacker footholds without removing your own visibility. In AD, persistence often hides as:

• Extra privileged group members or nested groups
• Backdoored GPOs or GPO links
• Delegation/ACL modifications on OUs, groups, and service accounts
• Unapproved service accounts / scheduled tasks on critical servers
• Hybrid connectors or sync paths abused to reintroduce changes

1) Remove privilege anomalies first

• Reconcile privileged group membership with an approved list.
• Remove unexpected nested groups.
• Review delegated rights at OUs where identity/admin objects live (Tier-0 zones).

If delegation sprawl is part of the story, use a least-privilege approach to unwind it: How to delegate OU permissions with minimal risk.

2) Hunt for “quiet” permission sprawl

Attackers love permissions because they persist through password resets. Review over-broad rights and legacy grants, especially on OUs containing privileged accounts, DC computer objects, and GPO management scopes. A useful mental model and remediation approach: Excess Permissions: Lessons from Legacy Setups.

3) Validate trust boundaries and cross-domain assumptions

If your incident involves multiple domains/forests, validate trust configurations and filtering behaviors. If you operate complex trust layouts, review SID filtering posture and related delegation guidance: SID filtering in complex AD layouts: expert guide & runbook.

4) Keep hybrid “reintroduction” from undoing your work

• Confirm whether changes originated on-prem or cloud and where “source of authority” sits for each object type.
• Disable/contain compromised sync/admin pathways long enough to stabilize identity.
• Audit cloud-side privileged role assignments and risky sign-ins in parallel.

Recovery: returning trust to the directory

Recovery is not “everything is green.” Recovery is: you can again trust that authentication and authorization outcomes are controlled by you, not an adversary.

Recovery sequence (recommended order)

1. Restore admin workstation hygiene: rebuild/validate privileged endpoints used for AD administration.
2. Re-establish privileged identity: confirm the integrity of privileged groups and administrative pathways.
3. Credential recovery in waves: prioritize Tier-0 accounts, then Tier-1 servers, then general users—avoiding outage cascades.
4. Validate GPO baseline: compare current GPOs vs known-good and reapply hardened baselines carefully.
5. Re-open controlled change: resume normal ops with heightened logging, alerting, and approval gates for privileged actions.

Prove recovery with verification checks

• Privileged group membership matches your approved roster.
• No unexpected GPO changes within monitored window.
• DCs show normal authentication patterns; no anomalous admin logons.
• EDR/identity detections stop triggering for the original behaviors.
• Replication is healthy and consistent (no lingering divergence across DCs).

After-action: hardening that prevents the next one

Most organizations “fix the symptom” and keep the same identity shape that enabled the incident. Your post-incident work should reduce the probability of repeat compromise and reduce blast radius.

1) Reduce attack surface in authentication

• Minimize legacy authentication where feasible; monitor where it still exists.
• Require stronger controls for privileged authentication (MFA/JIT, admin-only logon paths).
• Instrument high-signal identity detections and alert routing.

2) Make privilege “expensive” to obtain

• Clean up delegation and OU permissions (scope, audit, time-bound where possible).
• Remove legacy broad permissions and document the new model.
• Protect GPO management: limit who can edit, who can link, and alert on edits/links.

3) Improve response speed with rehearsals

• Run “first hour” tabletop exercises quarterly.
• Build automation for common queries (privileged group diff, recent GPO changes, DC admin logon list).
• Pre-approve containment actions that are reversible (isolation playbooks, account disable flows).

Printable checklists

First 15 minutes checklist

• Assign IC + scribe + technical leads
• Freeze privileged change windows
• Move admin activity to known-good admin host
• Confirm DC logs are collecting centrally (and retention is sufficient)
• Write down the initial anchor: account/host/time/symptom

First hour checklist

• Classify likely compromise level (user vs privileged vs DC/control plane)
• Contain narrowly: disable suspect account(s) and isolate suspect host(s)
• Diff privileged group memberships against expected roster
• Check recent GPO changes and new/changed GPO links
• Check for log tampering signals and audit policy changes
• Establish break-glass admin lane if trust is uncertain

Day 1 checklist

• Expand scoping: identify additional compromised accounts/hosts
• Remove persistence: privileged group anomalies, GPO backdoors, delegation/ACL changes
• Credential recovery plan in waves (Tier-0 → Tier-1 → users)
• Verify replication health and directory consistency
• Document final incident timeline and decisions

FAQ

Should we reset passwords immediately?

Only when you can do it safely. For a single compromised user, yes—reset and revoke sessions quickly. For privileged or service accounts, do staged resets with dependency awareness to avoid outages that help the attacker hide.

Should we reboot domain controllers to “kick out” the attacker?

Not as a first move. Reboots can destroy volatile evidence and complicate timeline reconstruction. Prefer containment: restrict admin logon paths, isolate compromised endpoints, and lock down privileged changes first.

What’s the fastest way to detect if the incident is tied to authentication issues?

Start with lockouts/failed logons (4625/4740 patterns), then look for privileged logons on DCs and recent privilege changes. If you’re actively troubleshooting lockout spikes, use: Account Lockout Event ID: How to Find Account Lockouts.

Hybrid question: can cloud logs help an on-prem AD incident?

Yes. Many identity compromises begin in cloud sign-in abuse and land on-prem through sync or admin reuse. Correlate Entra sign-ins, risky users, and audit trails with DC authentication and privileged actions: How to monitor and report security events in Microsoft Entra ID.