Event ID 4624: Your Secret Weapon for Uncovering Cyber Threats

In the relentless cat-and-mouse game of cybersecurity, attackers constantly seek footholds. One of the most consistently abused avenues? Remote Desktop Protocol (RDP). Whether it’s exposed to the wild web or used for lateral movement within your network, RDP is a prime target. But what if I told you one specific Windows event ID could be your ace in the hole for spotting this and other malicious activity?

Today, we’re diving deep into what might just be the most valuable event ID for your threat hunting arsenal: Windows Event ID 4624.

Why This Event ID is a Game-Changer for Threat Hunters

If you peek into the MITRE ATT&CK framework, specifically technique T1021.001 (Remote Desktop Protocol), you’ll see just how common this attack vector is. Attackers love RDP for moving across trust boundaries, be it from an external point into your network or internally between different zones.

Alarmingly, a quick search on services like Shodan can reveal millions of RDP instances exposed to the internet. While some are undoubtedly honeypots, a significant number are genuine, potentially vulnerable systems.

But even if your RDP isn’t internet-facing, don’t tune out. This event ID is still incredibly crucial. Imagine an attacker gains initial entry – perhaps via a phishing email and then deploys a tool like Mimikatz to harvest credentials. What’s often next? They might use those stolen credentials with RDP or another network-authenticated service to pivot and burrow deeper into your environment.

So, whether you’re worried about external RDP exposure or internal lateral movement, Event ID 4624 is your friend. It’s a go-to for tracking not just attacker activity but also potential insider threats.

Cracking Open Windows Event ID 4624: Successful Logons

So, what exactly is Windows Security Log Event ID 4624? In simple terms, it records every successful authentication request to a Windows machine.

This isn’t just a simple “someone logged in” message. It’s packed with valuable forensic data:

• Username: The account that logged in.
• Domain: The domain the account belongs to.
• Process: The process that initiated the logon.
• Source IP Address and Port: Where the login attempt originated from.
• Logon Type: This field is pure gold, and we’ll explore why in a moment.
• A wealth of other metadata for deeper analysis.

While we’re focusing on successful logons (4624), it’s also wise to keep an eye on Event ID 4625 (failed logons). But for today, 4624 is our star.

(Pro-tip: For an excellent free resource, check out the “Ultimate Windows Security’s Encyclopedia of Security Logs.” It often provides sample logs and field explanations, which is invaluable if you don’t have a specific event in your own logs yet.)

The Magic Ingredient: Understanding Logon Types

The “Logon Type” field within Event ID 4624 is where things get really interesting. This single field gives you critical context about how the logon occurred. Here are some of the most important Logon Types you need to know:

• Logon Type 2 (Interactive): This is your classic “at the keyboard” login. Someone is physically present at the console and logging into the machine.
• Logon Type 10 (RemoteInteractive): This is a big one for RDP abuse. It flags remote interactive logins, including RDP, Remote Assistance, and some Terminal Services. If you’re hunting for RDP activity, this is your primary filter.
  
  • Hunting Scenario: Filter for Logon Type 10. Are you seeing unexpected source IPs? Logins from administrative accounts to user workstations?
• Logon Type 3 (Network): Think mapped drives and accessing shared resources across the network. This happens when a user or service accesses a resource on another computer.
  
  • Hunting Scenario: A sudden spike in Type 3 logons from a workstation to multiple servers could indicate reconnaissance or data exfiltration attempts.
• Logon Type 4 (Batch): This indicates a scheduled task has run. Since attackers often use scheduled tasks for persistence (MITRE ATT&CK T1053), filtering for Type 4 logons can uncover malicious scheduled tasks.
  
  • Hunting Scenario: Look for Type 4 logons associated with unusual script names or processes, especially those running under high-privilege accounts.
• Logon Type 5 (Service): This is generated when a service starts.
• Logon Type 7 (Unlock): This signifies someone unlocking a locked session (e.g., after pressing Ctrl+Alt+Del and entering credentials).
• Logon Type 11 (CachedInteractive): This occurs when a user logs on with cached domain credentials, typically when a laptop is off the corporate network.
  
  • Hunting Scenario: Useful for understanding if domain controller logs will be present for that specific logon event (they likely won’t be if it’s cached).

By understanding these Logon Types, you can quickly discern between someone physically at a machine versus a remote RDP session, or a scheduled task versus a network share access. This context is vital for effective threat hunting.

Bringing it to Life: Analyzing Logs with Tools like ELK

Imagine sifting through gigabytes, even terabytes, of these logs. Manually, it’s a nightmare. This is where Security Information and Event Management (SIEM) tools or log analysis platforms like the ELK Stack (Elasticsearch, Logstash, Kibana) become indispensable.

You can ingest these Windows Event Logs (using methods like Elastic Beats, Logstash forwarders, or even custom scripts like evtx_to_elk if you’re dealing with raw EVTX files) and then build dashboards and queries to pivot through the data.

For example, you could easily filter by Logon Type, then look at the source IPs, usernames, and processes involved. You can see which processes are initiating which types of logons (e.g., user32.dll for cached interactive, advapi32.dll or other service processes for service logons). You can also see the account names, including Microsoft accounts (which might show up as an email address).

The ability to quickly slice and dice this data, search for specific text strings within raw logs, and visualize patterns is what elevates your threat hunting from tedious to powerful.

Brainstorming Your Threat Hunt with Event ID 4624

So, how do you turn this data into actionable intelligence? Here are a few starting points for your threat hunts using Event ID 4624:

1. 1. Baseline Your ‘Normal’:

      • What does typical login activity look like in your environment?
      • Which users normally log into which systems, and from where?
      • What are the common services and processes initiating logons?
      • What times of day are logons expected? Establishing a baseline is key to spotting deviations that could indicate malicious activity.

   2. Hunt for Anomalous RDP (Logon Type 10):

      • Are there connections from unexpected internal subnets or, if applicable, external IPs that shouldn’t be there?
      • Are privileged accounts (e.g., Domain Admins) RDPing to standard user workstations? This is highly suspicious.
      • Are there RDP sessions happening at unusual hours?

   3. Spot Out-of-Hours Activity & Unusual Account Usage:

      • If an attacker uses harvested credentials (perhaps via Mimikatz), they might not stick to the legitimate user’s normal working hours. Look for logins outside of expected shift schedules.
      • Are service accounts being used for interactive logons? This is often a red flag.

   4. Connect the Dots in an Attack Chain:

      • Event ID 4624 is powerful for timeline building. If you see a suspicious process execution or network connection, check the 4624 logs around that time. Did a suspicious remote login precede it? This can help you chain together different pieces of an attack.

   5. Investigate Scheduled Task Abuse (Logon Type 4):

      • Are new, unexpected batch logons (Type 4) appearing? Investigate the associated scheduled tasks.

These are just a few generic ideas. As you become more familiar with your environment and the specifics of your threat hunts, you’ll develop even more targeted hypotheses.

More Than Just RDP

While we’ve highlighted RDP, remember that Event ID 4624, with its various Logon Types, provides visibility into a wide range of authentication activities. It’s a foundational log source for uncovering many different MITRE ATT&CK techniques.

Final Thoughts

Windows Event ID 4624 is more than just a log entry; it’s a rich source of truth for understanding who is accessing your systems and how. By mastering its nuances, especially the different Logon Types, you significantly enhance your ability to detect, investigate, and respond to cyber threats.

So, start digging into your 4624 events. You might be surprised by what you find. Happy hunting!