Exfil Event Collection

Exfil (Event Collection)

The Exfil extension (ext-exfil) manages which real-time events EDR sensors send to LimaCharlie. By default, sensors send events based on a standard profile. This extension lets you customize what gets collected.

Core Concept

Event collection determines what data reaches LimaCharlie — and therefore what D&R rules can see. If an event type isn't collected, no D&R rule can detect it and no output will receive it. This is the most fundamental knob for balancing visibility vs throughput.

Gotcha: event collection rule changes sync with sensors every few minutes, NOT instantly. After changing rules, wait several minutes before expecting new behavior.

Three Rule Types

Event Collection Rules

Control which event types are sent per platform and tag combination.

{
  "action": "add_event_rule",
  "name": "windows-vip",
  "events": ["NEW_TCP4_CONNECTION", "NEW_TCP6_CONNECTION"],
  "tags": ["vip"],
  "platforms": ["windows"]
}

This means: for Windows sensors tagged vip, also collect TCP connection events.

Watch Rules

Conditional operators on events — only send events matching specific field values. Used to manage high-volume events by filtering at the sensor.

{
  "action": "add_watch",
  "name": "wininet-loading",
  "event": "MODULE_LOAD",
  "operator": "ends with",
  "value": "wininet.dll",
  "path": ["FILE_PATH"],
  "tags": ["server"],
  "platforms": ["windows"]
}

This means: for Windows sensors tagged server, only send MODULE_LOAD events where FILE_PATH ends with wininet.dll. All other MODULE_LOAD events are dropped at the sensor.

Performance Rules

For high I/O servers (Windows only). May impact event accuracy. Applied via tag to sensor sets.

{
  "action": "add_perf_rule",
  "name": "sql-servers",
  "tags": ["sql"],
  "platforms": ["windows"]
}

Throughput Management

Enabling ALL events via exfil can produce massive traffic. LimaCharlie processes events in real-time, but if the rate exceeds capacity, events are enqueued up to a limit. If that limit is reached, the queue is dropped and a DATA_DROPPED error is emitted to platform logs.

Seeing event collection errors means you need to:

1. Reduce the population of events collected
2. Reduce D&R rule count or complexity
3. Use Watch Rules to filter high-volume events at the sensor
4. Enable IR mode

Afterburner Mode

Before dropping a backlogged queue, LimaCharlie enters "Afterburner" mode automatically. This addresses the common scenario of spammy processes (e.g., devenv.exe or git called hundreds of times per second during builds):

1. De-duplicates spammy processes
2. Processes each unique process through D&R rules only once

Afterburner is automatic — no configuration needed.

IR Mode

For users who want to record a very large number of events but don't need D&R rules on all of them. Enable by tagging a sensor with ir.

When IR mode is enabled:

• Events are NOT de-duplicated (full fidelity recording)
• D&R rules ONLY run on these 4 event types:
  1. CODE_IDENTITY
  2. DNS_REQUEST
  3. NETWORK_CONNECTIONS
  4. NEW_PROCESS

Gotcha: IR mode means most D&R rules won't fire. Only use it when you explicitly need full event recording with limited detection. This affects managed rulesets too — Soteria rules that depend on other event types won't fire.

CLI Operations

The exfil extension is managed via extension requests:

# List all exfil rules
limacharlie extension request --name ext-exfil --action list_rules --oid <oid> --output yaml

# Add event collection rule
limacharlie extension request --name ext-exfil --action add_event_rule --data '{"name":"windows-extra","events":["NEW_TCP4_CONNECTION"],"tags":["monitor"],"platforms":["windows"]}' --oid <oid> --output yaml

# Remove event collection rule
limacharlie extension request --name ext-exfil --action remove_event_rule --data '{"name":"windows-extra"}' --oid <oid> --output yaml

# Add watch rule
limacharlie extension request --name ext-exfil --action add_watch --data '{"name":"wininet-only","event":"MODULE_LOAD","operator":"ends with","value":"wininet.dll","path":["FILE_PATH"],"tags":["server"],"platforms":["windows"]}' --oid <oid> --output yaml

# Remove watch rule
limacharlie extension request --name ext-exfil --action remove_watch --data '{"name":"wininet-only"}' --oid <oid> --output yaml

Gotchas Summary