Detection: Ngrok Reverse Proxy on Network

Updated Date: 2026-05-13 ID: 5790a766-53b8-40d3-a696-3547b978fcf0 Author: Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects DNS queries to common Ngrok domains, indicating potential use of the Ngrok reverse proxy tool. It leverages the Network Resolution datamodel to identify queries to domains such as ".ngrok.com" and ".ngrok.io". While Ngrok usage is not inherently malicious, it has been increasingly adopted by adversaries for covert communication and data exfiltration. If confirmed malicious, this activity could allow attackers to bypass network defenses, establish persistent connections, and exfiltrate sensitive data, posing a significant threat to the network's security.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Network_Resolution
 3  WHERE DNS.query IN ("*.ngrok.com","*.ngrok.io", "ngrok.*.tunnel.com", "korgn.*.lennut.com")
 4  BY DNS.answer DNS.answer_count DNS.query
 5     DNS.query_count DNS.reply_code_id DNS.src
 6     DNS.vendor_product
 7
 8| `drop_dm_object_name("DNS")`
 9
10| `security_content_ctime(firstTime)`
11
12| `security_content_ctime(lastTime)`
13
14| `ngrok_reverse_proxy_on_network_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 22	Windows	`'XmlWinEventLog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
ngrok_reverse_proxy_on_network_filter	`search *`

ngrok_reverse_proxy_on_network_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1090	Proxy	Command and Control
T1102	Web Service	Command and Control
T1572	Protocol Tunneling	Command and Control

Command and Control

DE.AE

CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Finding (Notable)	No
Creates Intermediate Finding (Risk Event)	Yes

Anomaly detections generate Intermediate Findings (Risk Events). They do not generate a Finding (Notable) directly.

Implementation

The Network Resolution Datamodel will need to have data mapped to it regarding DNS queries. Modify query as needed to use another source.

Known False Positives

False positives will be present based on organizations that allow the use of Ngrok. Filter or monitor as needed.

Associated Analytic Story

Intermediate Findings

Message	Entity Field	Entity Type	Risk Score
An endpoint, $src$, is beaconing out to the reverse proxy service of Ngrok.	src	system	20

References

https://www.cisa.gov/uscert/sites/default/files/publications/aa22-320a_joint_csa_iranian_government-sponsored_apt_actors_compromise_federal%20network_deploy_crypto%20miner_credential_harvester.pdf

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 10