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How CVE-2026-44025 Works
Fluentd’s Monitor Agent plugin (in_monitor_agent) is designed to expose internal metrics and plugin information via a REST API for monitoring purposes. This plugin provides several endpoints, including `/api/plugins.json` and related paths, which return detailed information about the loaded plugins and their status.
The vulnerability arises because the API response unintentionally includes internal instance variables of all loaded plugins. In Ruby, instance variables (prefixed with @) can hold any type of data, including sensitive configuration values such as database passwords, API keys, cloud credentials, or other secrets that a plugin might store internally.
An attacker who can reach the Monitor Agent API port (default: 24220) can send a simple HTTP GET request to `/api/plugins.json` and receive a JSON response containing these instance variables in plain text. If any configured plugin stores sensitive information in its instance variables, that information will be exposed directly in the API response.
The impact of this vulnerability depends heavily on the network configuration. If the Monitor Agent port is bound to `0.0.0.0` (all interfaces) or is exposed to untrusted networks, an attacker can retrieve sensitive credentials without any authentication. The vulnerability is classified as High severity with a CVSS v3 score of 7.5/10.
The flaw was addressed in Fluentd v1.19.3 by changing the default behavior of the Monitor Agent API. In the patched version, the API no longer exposes sensitive instance variables by default. Administrators who need the previous behavior can explicitly enable certain parameters (include_config, include_retry, include_debug_info), but these are now disabled by default for security.
DailyCVE Form:
Platform: ....... Fluentd Version: ........ v1.19.2 and earlier Vulnerability :...... Information Disclosure Severity: ....... High (CVSS 7.5) date: .......... 2026-06-25 Prediction: 2026-06-26 (Patched in v1.19.3)
What Undercode Say:
Analytics:
The vulnerability exposes internal instance variables of all loaded plugins via the Monitor Agent API. This is particularly dangerous because many plugins store credentials in instance variables for runtime use. The exposure is passive—an attacker only needs network access to the API port to retrieve the data. No authentication or special privileges are required.
Bash Commands & Codes:
Check if the Monitor Agent is exposed
curl -s http://<target-ip>:24220/api/plugins.json | jq '.'
Extract sensitive fields from plugin instances
curl -s http://<target-ip>:24220/api/plugins.json | jq '.plugins[].instance | with_entries(select(.key | startswith("@")) )'
Check for specific sensitive patterns (example: password, secret, key)
curl -s http://<target-ip>:24220/api/plugins.json | grep -iE 'password|secret|key|token|credential'
Verify binding address (should be 127.0.0.1, not 0.0.0.0)
grep -r "monitor_agent" /etc/fluent/fluent.conf
Exploit:
An attacker can exploit this vulnerability by sending a GET request to the Monitor Agent API endpoint. If the API is bound to `0.0.0.0` or is accessible from the attacker’s network, the response will contain all plugin instance variables in plain text. Any sensitive data stored in these variables—such as database credentials, cloud provider keys, or API tokens—will be exposed.
Example exploit:
curl http://<target-ip>:24220/api/plugins.json
The attacker can then parse the JSON response to extract any fields that appear to contain sensitive information.
Protection:
- Update to Fluentd v1.19.3 or later – This is the primary fix.
2. Bind the Monitor Agent to localhost only:
<source> @type monitor_agent bind 127.0.0.1 port 24220 </source>
3. Restrict network access – Use firewall rules (iptables, AWS Security Groups, etc.) to block access to port `24220` from untrusted networks.
4. Disable sensitive parameter exposure – In v1.19.3+, ensure include_config, include_retry, and `include_debug_info` are set to `false` (the default).
Impact:
- Unauthorized Information Disclosure – An attacker can retrieve sensitive credentials used by Fluentd plugins.
- Data Breach – Exposed credentials can lead to further compromise of databases, cloud services, or other integrated systems.
- Lateral Movement – Attackers may use stolen credentials to access other parts of the infrastructure.
- Compliance Violations – Exposure of sensitive data may violate regulatory requirements (e.g., GDPR, PCI-DSS).
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Sources:
Reported By: github.com
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