CVE-2026-44024 in Fluentd
Summary
by MITRE • 07/09/2026
Fluentd collects events from various data sources and writes them to files, RDBMS, NoSQL, IaaS, SaaS, Hadoop and so on. Prior to 1.19.3, Fluentd allows dynamically constructing file paths using the ${tag} placeholder, and insufficient validation of ${tag} in file configurations such as the path parameter of the out_file plugin allows attackers sending untrusted tags containing path traversal characters to write or overwrite arbitrary files and potentially achieve remote code execution. This issue is fixed in version 1.19.3.
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Analysis
by VulDB Data Team • 07/09/2026
Fluentd serves as a comprehensive data collection and logging platform that aggregates events from diverse sources and forwards them to various storage systems including files, relational and non-relational databases, cloud infrastructure services, and big data platforms. The vulnerability resides within the file path construction mechanism of the out_file plugin where the system dynamically generates file paths using the ${tag} placeholder. This placeholder substitution process creates a critical security gap when the tag values are not properly validated or sanitized before being used in file system operations.
The technical flaw manifests through insufficient input validation of the ${tag} parameter within file configuration settings, specifically affecting the path attribute of the out_file plugin. Attackers can exploit this vulnerability by crafting malicious tags containing path traversal sequences such as ../ or ..\ that bypass normal validation checks. When these untrusted tag values are processed through the dynamic path construction logic, they enable attackers to manipulate the intended file destination and write data to arbitrary locations on the file system. This path traversal vulnerability extends beyond simple file creation to encompass file overwriting capabilities, providing attackers with persistent access to target systems.
The operational impact of this vulnerability spans multiple security domains including privilege escalation, data integrity compromise, and potential remote code execution. An attacker who can inject malicious tags into the logging pipeline can leverage this vulnerability to overwrite critical system files, inject malicious content into log files that may be processed by other applications, or establish persistence mechanisms through file manipulation. The vulnerability's severity is amplified because it affects a core functionality of Fluentd's data handling capabilities and can be exploited through normal data ingestion channels without requiring elevated privileges.
Security practitioners should implement immediate mitigations including upgrading to Fluentd version 1.19.3 which contains the necessary fixes for this vulnerability. Organizations must also establish robust input validation policies for all tag values, implement proper sanitization of dynamic path components, and monitor file system access patterns for suspicious activity. The vulnerability aligns with CWE-22 Path Traversal and CWE-74 Injection flaws, while also mapping to ATT&CK techniques involving privilege escalation through file system manipulation and persistence mechanisms. Additional defensive measures include restricting write permissions for Fluentd processes, implementing network segmentation for logging infrastructure, and deploying monitoring solutions that can detect anomalous file system operations originating from logging services.
The fix implemented in version 1.19.3 addresses the core validation issue by introducing stricter sanitization of tag values before path construction occurs. This includes automatic escaping of special characters, enforcement of whitelist-based tag validation, and implementation of comprehensive input filtering for all dynamic path components. Security teams should also consider implementing additional controls such as file integrity monitoring, regular security assessments of logging configurations, and establishing clear policies for tag management within distributed logging environments to prevent similar vulnerabilities from emerging in other components of the data pipeline.