The Community ID is a standardized flow hash that generates a unique identifier for a network connection. Since it's implemented across multiple tools, it allows for tracking events associated with the same connection across different systems. This is particularly valuable for correlating network and endpoint events.
For instance, when using Suricata or Zeek for network visibility alongside Sysmon or a full-fledged EDR for endpoint telemetry, a core challenge is seamlessly linking these two types of events to answer questions like:
- Which files were accessed or modified by the process behind this network activity?
- Which user was logged in when this potentially malicious DNS request was made?
- What other network connections were established by the same process that communicated with this C2 server?
- Which process initiated this TLS-encrypted network connection that just matched a JA4 fingerprint?
- What application is responsible for this anomalous-looking network traffic?
Let's make this more tangible with a concrete example. Consider this Zeek connection event:
{
"ts": "2024-08-29T12:34:56.789Z",
"uid": "CZwqhx3td8eTfCSwJb",
"id": {
"orig_h": "192.168.1.100",
"orig_p": 65432,
"resp_h": "93.184.216.34",
"resp_p": 80
},
"proto": "tcp",
"service": "http",
"duration": "5.16s",
"orig_bytes": 205,
"resp_bytes": 278,
"conn_state": "SF",
"missed_bytes": 0,
"history": "ShADadfF",
"orig_pkts": 6,
"orig_ip_bytes": 525,
"resp_pkts": 5,
"resp_ip_bytes": 546,
"community_id": "1:7rgwE/NtiMlsxtm1e9OpqJ3icU0="
}
This log reflects an HTTP connection from 192.168.1.100 to 93.184.216.34. On
the endpoint, this activity might correspond to a Sysmon event like this:
{
"Event": {
"System": {
"Provider": {
"Name": "Microsoft-Windows-Sysmon",
"Guid": "{5770385f-c22a-43e0-bf4c-06f5698ffbd9}"
},
"EventID": 3,
"Version": 5,
"Level": 4,
"Task": 3,
"Opcode": 0,
"Keywords": "0x8000000000000000",
"TimeCreated": {
"SystemTime": "2024-08-29T12:34:56.789Z"
},
"EventRecordID": 12345678,
"Correlation": {},
"Execution": {
"ProcessID": 4567,
"ThreadID": 8901
},
"Channel": "Microsoft-Windows-Sysmon/Operational",
"Computer": "DESKTOP-EXAMPLE",
"Security": {
"UserID": "S-1-5-18"
}
},
"EventData": {
"RuleName": "NetworkConnection",
"UtcTime": "2024-08-29 12:34:56.789",
"ProcessGuid": "{ABCDEF01-1234-5678-90AB-CDEF12345678}",
"ProcessId": 1234,
"Image": "C:\\Windows\\System32\\svchost.exe",
"User": "NT AUTHORITY\\SYSTEM",
"Protocol": "tcp",
"Initiated": "true",
"SourceIsIpv6": "false",
"SourceIp": "192.168.1.100",
"SourceHostname": "DESKTOP-EXAMPLE",
"SourcePort": 65432,
"SourcePortName": null,
"DestinationIsIpv6": "false",
"DestinationIp": "93.184.216.34",
"DestinationHostname": "example.com",
"DestinationPort": 80,
"DestinationPortName": "http"
}
}
}
How would you pivot between these two events if given only one of them? This is
where the Community ID shines. The Zeek event already has a Community ID:
1:YXWfTYEyYLKVv5Ge4WqijUnKTrM=, but the Sysmon event doesn't.
Luckily, you can compute the Community ID retroactively because all the
necessary information is present in the Sysmon event. With Tenzir's pipelined
query language (TQL), you can generate the Community ID by passing the
relevant fields to the community_id function like this:
// tql2
from "sysmon.json"
CommunityID = community_id(
src_ip=Event.EventData.SourceIp,
src_port=Event.EventData.SourcePort,
dst_ip=Event.EventData.DestinationIp,
dst_port=Event.EventData.DestinationPort,
proto=Event.EventData.Protocol,
)
When you run the pipeline, the output will now include an extra field:
{
"Event": {
// ... other fields ...
},
"CommunityID": "1:7rgwE/NtiMlsxtm1e9OpqJ3icU0="
}
There you go! In your analytics environment, you can now pivot between these two events by simply following the value of the Community ID.
Whether you’re building out an XDR stack, enhancing your threat hunting capabilities, or responding to incidents, having a flexible data integration layer is crucial. Tenzir has you covered. Our data pipeline engine is security-first and supports much more than just Community ID computation. Check out our free Community Edition to try it yourself, or join our friendly Discord community to learn more.