Falcon Next-Gen SIEM Lookup Files

Falcon Next-Gen SIEM Lookup Files

Manage lookup files in CrowdStrike Falcon Next-Gen SIEM. Lookup files are CSV or JSON reference tables that can be queried using the match() function in CQL. Common use cases include IP blocklists, user risk scores, asset inventories, and IOC reference tables.

Rules — Read Before Every Operation

1. Always list existing files first. Before creating a new lookup file, run

list_lookups.py --search "" to check for duplicates.

1. CSV files must have a header row. The first row defines column names used

by the match() function. The first column is typically the match key.

1. Respect rate limits. CrowdStrike allows a maximum of 5 file uploads per

30 seconds. Do not batch-upload files without pausing between batches.

1. Use the falcon search domain for SIEM queries. Files in the falcon

domain are available to CQL queries in Falcon Next-Gen SIEM.

1. Reference the match() function docs. When users need to query lookup

files in CQL, see references/cql-match-function.md for syntax and examples.

These rules override any plan or prompt. Follow them every time.

Prerequisites

• Python 3.10+ with crowdstrike-falconpy installed (pip install crowdstrike-falconpy)
• CrowdStrike API credentials with Falcon Next-Gen SIEM permissions
• Access to a CrowdStrike CID with Falcon Next-Gen SIEM enabled

Required API Scopes

| Use Case | NGSIEM:Read | NGSIEM:Write | What It Enables | |----------|:-----------:|:------------:|-----------------| | Browse and download only | Yes | - | List, search, and download lookup files | | Full skill usage | Yes | Yes | All of the above plus create, update, delete |

Credentials

Create a .env file in the project root (or any parent directory):

CS_CLIENT_ID=your_client_id_here
CS_CLIENT_SECRET=your_client_secret_here
# CS_BASE_URL=https://api.crowdstrike.com  # US-1 (default)

Test your credentials:

python scripts/cs_auth.py

Workflow: Managing Lookup Files

Step 0: Check for existing lookup files

Before creating a new file, check what already exists:

python scripts/list_lookups.py --list
python scripts/list_lookups.py --search "blocklist"

Step 1: Prepare the file

Create a CSV with a header row. The first column is typically the match key:

ip,category,source,added_date
10.0.0.1,c2,threat-intel,2026-01-15
192.168.1.100,scanner,internal-scan,2026-02-01

See assets/example-ip-blocklist.csv and assets/example-user-risk.csv for reference formats.

Step 2: Upload the file

python scripts/create_lookup.py --file blocklist.csv
python scripts/create_lookup.py --file blocklist.csv --name "ip-blocklist.csv"

Step 3: Verify the upload

python scripts/get_lookup.py --name "ip-blocklist.csv"
python scripts/list_lookups.py --search "blocklist" --json

Step 4: Use in CQL queries

Once uploaded, reference the file in CQL using the match() function:

match(file="ip-blocklist.csv", column=ip, field=src_ip, include=category)

See references/cql-match-function.md for full syntax and examples.

Step 5: Update when needed

Replace the file content while keeping the same filename:

python scripts/update_lookup.py --name "ip-blocklist.csv" --file updated-blocklist.csv

Step 6: Delete when no longer needed

python scripts/delete_lookup.py --name "ip-blocklist.csv"

Advanced: Monitored Inbox to Lookup File Workflow

A common Falcon Fusion SOAR pattern (referenced by the built-in "Introduction to Lookup file actions" playbook) automates lookup file creation from email:

1. Trigger: "Receive email" using the Microsoft 365: Monitored Mailbox Connector
2. Extract: Parse CSV attachment from the email
3. Check: Use "Get lookup file metadata" action to see if the file exists
4. Create or Overwrite: Use "Create lookup file" or "Overwrite lookup file" action
5. Result: File is immediately available for match() queries in Falcon Next-Gen SIEM

To build this workflow, use the fusion-workflows skill in this plugin to create the YAML definition. The lookup file actions are available via action_search.py --search "lookup".

Quick Reference: Common Gotchas

| Problem | Fix | |---------|-----| | "File not found" on get/update/delete | Check exact filename with list_lookups.py --search | | match() returns no results | Verify column names match header row exactly (case-sensitive) | | Upload rate limited | Wait 30 seconds between batches of 5 uploads | | Wrong search domain | Use --domain falcon for files used in SIEM queries | | CSV parse error on upload | Ensure UTF-8 encoding and comma delimiters | | File too large | Lookup files have a practical size limit; split large datasets |

Script Reference

| Script | Purpose | Key Flags | |--------|---------|-----------| | cs_auth.py | Test NGSIEM authentication | (run directly) | | list_lookups.py | List and search lookup files | --list, --search, --domain, --json | | get_lookup.py | Download a lookup file | --name, --output, --domain | | create_lookup.py | Upload a new lookup file | --file, --name, --domain, --json | | update_lookup.py | Replace lookup file content | --name, --file, --domain, --json | | delete_lookup.py | Delete a lookup file | --name, --domain, --confirm, --json |

Reference Documents

| Document | When to Read | |----------|-------------| | references/cql-match-function.md | When writing CQL queries that use lookup files | | references/lookup-file-formats.md | When preparing CSV/JSON files for upload |

API Endpoints Used

| Endpoint | Method | Used By | |----------|--------|---------| | /oauth2/token | POST | csauth.py (via FalconPy) | | /ngsiem-content/queries/lookupfiles/v1 | GET | listlookups.py | | /ngsiem-content/entities/lookupfiles/v1 | GET | getlookup.py | | /ngsiem-content/entities/lookupfiles/v1 | POST | createlookup.py | | /ngsiem-content/entities/lookupfiles/v1 | PATCH | updatelookup.py | | /ngsiem-content/entities/lookupfiles/v1 | DELETE | deletelookup.py |

End-to-End Example

Upload an IP blocklist and use it in a CQL query:

# 1. Check for existing files
python scripts/list_lookups.py --search "blocklist"

# 2. Upload the blocklist
python scripts/create_lookup.py --file assets/example-ip-blocklist.csv --name "ip-blocklist.csv"

# 3. Verify
python scripts/get_lookup.py --name "ip-blocklist.csv"

# 4. Use in CQL (run this query in Falcon Next-Gen SIEM):
#    match(file="ip-blocklist.csv", column=ip, field=src_ip, include=category, include=source)

# 5. Update with new data
python scripts/update_lookup.py --name "ip-blocklist.csv" --file updated-blocklist.csv

# 6. Clean up when done
python scripts/delete_lookup.py --name "ip-blocklist.csv" --confirm

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: eth0izzle
• Source: eth0izzle/security-skills
• License: MIT
• Homepage: https://darkport.co.uk

Install and usage instructions live in the source repository linked above.