Path Traversal in Fluentd via Tag Placeholder

Executive Summary

This vulnerability exists in Fluentd versions prior to 1.19.3. Fluentd allows dynamic construction of file paths using the ${tag} placeholder. However, there is insufficient validation of the ${tag} value in file configurations such as the path parameter of the out_file plugin. Attackers can exploit this by sending untrusted tags containing path traversal characters, which enables them to write or overwrite arbitrary files on the system.

This can potentially lead to remote code execution, as attackers may place malicious files or overwrite critical files.

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Impact Analysis

The vulnerability can have severe impacts including unauthorized file write or overwrite on the affected system. This can lead to remote code execution, allowing attackers to run arbitrary code with the privileges of the Fluentd process.

Such an exploit can compromise the integrity, confidentiality, and availability of the system and its data.

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Mitigation Strategies

To mitigate this vulnerability, upgrade Fluentd to version 1.19.3 or later, where the issue with insufficient validation of the ${tag} placeholder in file path configurations has been fixed.

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Compliance Impact

CVE-2026-44024 is a critical remote code execution vulnerability in Fluentd that allows attackers to write or overwrite arbitrary files via path traversal in the ${tag} placeholder. This can lead to full system compromise, including unauthorized modification of files and configurations.

Such a vulnerability can impact compliance with common standards and regulations like GDPR and HIPAA because it threatens the confidentiality, integrity, and availability of sensitive data processed or logged by Fluentd. Unauthorized file writes and potential remote code execution could lead to data breaches, unauthorized access to personal or protected health information, and disruption of logging systems critical for audit and monitoring requirements.

Therefore, organizations using vulnerable versions of Fluentd may face increased risk of non-compliance with data protection regulations that mandate strict controls over data integrity and security.

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Detection Guidance

This vulnerability can be detected by monitoring Fluentd configurations and logs for the use of the `${tag}` placeholder in file path parameters, especially in the out_file plugin, and checking for tags containing path traversal characters such as "../" or absolute paths.

Suggested detection steps include:

• Review Fluentd configuration files for usage of `${tag}` in file path settings.
• Search Fluentd logs for unusual or suspicious tags containing path traversal patterns like "../" or absolute paths.
• Use commands to find configuration lines with `${tag}`, for example:
• grep -r '\${tag}' /path/to/fluentd/config/
• Check running Fluentd processes and their versions to ensure they are updated to 1.19.3 or later:
• fluentd --version
• Monitor network traffic to Fluentd input ports for tags containing suspicious path traversal sequences.

Mitigations include restricting network access to Fluentd input ports, running Fluentd as a non-root user, avoiding use of `${tag}` with untrusted input, and filtering incoming tags to block path traversal characters.

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