Quick Malware Analysis: KOI LOADER/KOI STEALER INFECTION pcap from 2025-07-08

Thanks to Brad Duncan for sharing this pcap from 2025-07-08 on his malware traffic analysis site! Due to issues with Google flagging a warning for the site, we're not including the actual hyperlink but it should be easy to find.

We did a quick analysis of this pcap using Security Onion 2.4.160:

https://blog.securityonion.net/2025/06/security-onion-24160-now-available.html

If you'd like to follow along, you can do the following:

• install Security Onion 2.4.160 in a VM:
  https://docs.securityonion.net/en/2.4/first-time-users.html
• import the pcap using the SOC Grid interface:
  https://docs.securityonion.net/en/2.4/grid.html#icons-in-lower-left-corner
• optionally enable the DNS lookups feature:
  https://docs.securityonion.net/en/2.4/soc-customization.html?#reverse-dns-lookups
• if you are a Security Onion Pro customer, set up our MCP server:
  https://docs.securityonion.net/en/2.4/mcp.html

The screenshots at the bottom of this post show some of the interesting alerts and their associated AI Summaries and Guided Analysis. At the end, we use the new MCP server (available to Security Onion Pro customers) to ask a few questions and get some nicely formatted reports back. 

Keep in mind that this is not some contrived demo, we simply downloaded a recent malware PCAP from Brad Duncan's site and imported it into Security Onion. Also keep in mind that this was just a PCAP and so there was no endpoint data. Had there been endpoint data, the results would have been even more in-depth.

Want more practice? Check out our other Quick Malware Analysis posts at:

https://blog.securityonion.net/search/label/quick%20malware%20analysis

About Security Onion

Security Onion is a versatile and scalable platform that can run on small virtual machines and can also scale up to the opposite end of the hardware spectrum to take advantage of extremely powerful server-class machines.  Security Onion can also scale horizontally, growing from a standalone single-machine deployment to a full distributed deployment with tens or hundreds of machines as dictated by your enterprise visibility needs. To learn more about Security Onion, please see:
https://securityonion.net

Screenshots

Let's start with an overview of all logs generated by Security Onion:

Now let's look at just the alerts:

We can switch the view to Ungroup to see a little more detail:

Next, let's drill into the first alert ("ET MALWARE Win32/Koi Stealer CnC Checkin (GET)"), review the AI Summary on the right, and then start going through its Guided Analysis questions:

Now let's drill into the second alert ("ET ATTACK_RESPONSE Koi Loader/Stealer CnC Config Inbound"), review the AI Summary on the right, and then start going through its Guided Analysis questions:

Now let's drill into the third alert ("ET INFO Windows Powershell User-Agent Usage"), review the AI Summary on the right, and then start going through its Guided Analysis questions:

If you're a Security Onion Pro customer, then you can set up our MCP Server (https://docs.securityonion.net/en/2.4/mcp.html) and then start asking questions and getting nicely formatted reports. For example, we can ask to investigate all alerts for July 8:

Finally, we can ask to investigate all HTTP traffic for July 8: