CVE-2026-44025: Fluentd Information Disclosure Flaw

CVE-2026-44025 Overview

CVE-2026-44025 is an information disclosure vulnerability in Fluentd, an open-source data collector used to unify logging across files, databases, cloud services, and SaaS platforms. The Monitor Agent plugin in_monitor_agent exposes internal metrics and plugin information through a REST API. Responses from /api/plugins.json and related endpoints unintentionally include internal instance variables that may contain database passwords, API keys, and cloud credentials. The issue affects Fluentd versions prior to 1.19.3 and is classified under [CWE-306: Missing Authentication for Critical Function].

Critical Impact
Unauthenticated attackers reachable to the Monitor Agent endpoint can retrieve plaintext credentials for downstream databases, SaaS APIs, and cloud provider accounts.

Affected Products

Fluentd versions prior to 1.19.3
Deployments enabling the in_monitor_agent plugin
Container and Kubernetes logging stacks bundling vulnerable Fluentd releases

Discovery Timeline

2026-07-08 - CVE-2026-44025 published to NVD
2026-07-08 - Last updated in NVD database

Technical Details for CVE-2026-44025

Vulnerability Analysis

Fluentd's Monitor Agent plugin exposes runtime state over HTTP for observability. The API serializes plugin instance variables when clients request /api/plugins.json and related endpoints. Because plugin configuration objects hold connection settings, the serialized response includes credentials that operators pass to output plugins. These credentials commonly include database passwords, cloud storage access keys, and third-party API tokens.

The Monitor Agent does not require authentication by default. Any actor able to reach the listener port can enumerate every configured plugin and read its internal state. In clustered logging deployments the port is frequently reachable across the internal network, expanding the blast radius beyond the local host.

Root Cause

The root cause is over-permissive default visibility for configuration, retry, and debug information in in_monitor_agent. The plugin defaulted include_config and include_retry to true, causing serialization of instance variables that hold secrets. Version 1.19.3 flips these defaults to false and adds an explicit include_debug_info flag, also defaulting to false.

Attack Vector

The vulnerability is exploitable over the network without authentication or user interaction. An attacker sends a GET request to the Monitor Agent endpoint and parses the JSON response for secrets embedded in plugin instance variables.

ruby

     desc 'Determine the rate to emit internal metrics as events.'
     config_param :emit_interval, :time, default: 60
     desc 'Determine whether to include the config information.'
-    config_param :include_config, :bool, default: true
+    config_param :include_config, :bool, default: false
     desc 'Determine whether to include the retry information.'
-    config_param :include_retry, :bool, default: true
+    config_param :include_retry, :bool, default: false
+    desc 'Determine whether to include the debug information.'
+    config_param :include_debug_info, :bool, default: false
 
     class APIHandler
       def initialize(agent)

Source: GitHub Commit 9909215. The patch changes plugin default visibility so sensitive fields are excluded from Monitor Agent responses unless an operator explicitly opts in.

Detection Methods for CVE-2026-44025

Indicators of Compromise

Unexpected inbound HTTP requests to the Monitor Agent listener, particularly to /api/plugins.json, /api/config.json, or /api/plugins.
Access log entries showing enumeration of monitor endpoints from hosts outside the observability control plane.
Downstream service authentication anomalies using credentials configured in Fluentd output plugins.

Detection Strategies

Inspect Fluentd process configuration for @type monitor_agent blocks and verify whether include_config or include_retry are enabled.
Perform an authenticated request to /api/plugins.json on each Fluentd instance and confirm sensitive fields are absent from the response body.
Correlate outbound authentication events from data destinations, such as PostgreSQL, S3, or Elasticsearch, with the Fluentd source host to identify credential reuse.

Monitoring Recommendations

Alert on any external network connection to the Monitor Agent bind port, typically TCP 24220.
Track secret rotation state and flag credentials configured in Fluentd that have not been rotated after the patch date.
Ingest Fluentd access logs into a central log platform and build detections for repeated /api/plugins queries from a single client.

How to Mitigate CVE-2026-44025

Immediate Actions Required

Upgrade Fluentd to version 1.19.3 or later on every collector, aggregator, and forwarder node.
Rotate all credentials previously configured in Fluentd output plugins, including database passwords, cloud access keys, and API tokens.
Restrict network reachability to the Monitor Agent port using host firewalls, Kubernetes NetworkPolicy, or security groups.

Patch Information

The fix ships in Fluentd 1.19.3. Details are available in the GitHub Security Advisory GHSA-pr7j-96cj-549h, the GitHub Release v1.19.3, and GitHub Pull Request #5392. The patch changes default visibility of include_config, include_retry, and introduces include_debug_info with a false default.

Workarounds

Disable the in_monitor_agent plugin entirely if runtime metrics are not required.
Explicitly set include_config false and include_retry false in the Monitor Agent configuration on unpatched instances.
Bind the Monitor Agent to 127.0.0.1 and require access through an authenticated reverse proxy or SSH tunnel.

bash

# Configuration example: harden in_monitor_agent on Fluentd < 1.19.3
<source>
  @type monitor_agent
  bind 127.0.0.1
  port 24220
  include_config false
  include_retry false
</source>