Remote Code Execution in Fluentd out_http Plugin

Executive Summary

This vulnerability exists in the Fluentd out_http output plugin prior to version 1.19.3. The plugin allows the use of placeholders such as ${tag} in the endpoint configuration parameter. If the placeholder value is derived from untrusted input, an attacker can manipulate it to control the destination hostname of outbound HTTP requests. This means the attacker can force Fluentd to send requests to arbitrary internal services.

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Impact Analysis

The vulnerability can allow an attacker to redirect outbound HTTP requests from Fluentd to arbitrary internal services. This can lead to unauthorized access or interaction with internal systems that are not intended to be exposed, potentially causing information disclosure or disruption of services.

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Mitigation Strategies

To mitigate this vulnerability, upgrade Fluentd to version 1.19.3 or later, where the issue has been fixed.

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Compliance Impact

The vulnerability allows an attacker to control the destination hostname of outbound HTTP requests from Fluentd, potentially forcing requests to arbitrary internal services. This can lead to unauthorized access to internal APIs and data exfiltration.

Such unauthorized data access and exfiltration risks could impact compliance with data protection regulations like GDPR and HIPAA, which require strict controls over personal and sensitive data to prevent unauthorized disclosure.

Until the vulnerability is patched, organizations must implement mitigations such as avoiding dynamic hostnames, restricting network access via firewall rules, or explicitly restricting allowed hosts to reduce the risk of data breaches that could violate these regulations.

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Detection Guidance

This vulnerability involves the Fluentd out_http plugin allowing dynamic hostnames via placeholders, which can be manipulated to send HTTP requests to arbitrary internal services.

To detect exploitation attempts or presence of this vulnerability on your system or network, you can:

• Check Fluentd configuration files for usage of the out_http plugin with dynamic placeholders (e.g., ${tag}) in the endpoint parameter.
• Verify the Fluentd version; versions prior to 1.19.3 are vulnerable.
• Monitor outbound HTTP requests from Fluentd for unusual or unexpected destination hostnames, especially internal IP addresses or hostnames.

Suggested commands to assist in detection:

• Use grep to find dynamic placeholders in Fluentd configuration files: grep -r 'out_http' /path/to/fluentd/conf | grep '\${'
• Check Fluentd version: fluentd --version
• Use network monitoring tools (e.g., tcpdump or Wireshark) to capture outbound HTTP traffic from the Fluentd host and filter for suspicious destination IPs or hostnames.
• Example tcpdump command: tcpdump -i any -n dst port 80 or dst port 443 and host <fluentd_host_ip>

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