Summary
Fluentd is Vulnerable to Remote Code Execution (RCE) via Arbitrary File Write in ${tag} Placeholder
Fluentd allows dynamically constructing file paths using the ${tag} placeholder.
It was discovered that validation for this placeholder was insufficient.
If a Fluentd instance is configured to receive logs from untrusted sources and uses the ${tag} placeholder in file configurations (such as the path parameter in the out_file plugin), an attacker can inject path traversal characters (e.g., ../).
When combined with certain formatting options, this vulnerability allows an attacker to write arbitrary files or overwrite existing files on the system with attacker-controlled content, bypassing intended directory restrictions.
Workarounds
If an immediate upgrade is not possible, users are strongly advised to apply the following mitigations:
- Restrict Network Access
- Ensure that Fluentd input ports (such as
in_forwardon default port24224) are deployed within a closed, trusted network. Use firewall rules (e.g., iptables, AWS Security Groups) to block access from untrusted networks or instances.
- Ensure that Fluentd input ports (such as
- Run Fluentd as a non-root user
- Dropping privileges prevents Fluentd from writing to sensitive system directories (e.g.,
/etc/), significantly mitigating the risk of system-wide RCE.
- Dropping privileges prevents Fluentd from writing to sensitive system directories (e.g.,
- Revise configurations
- Do not use the
${tag}placeholder in thepathparameter of output plugins (likeout_file) if the tag originates from an untrusted source.
- Do not use the
- Filter incoming tags
- Strictly validate and filter incoming tags at the input layer (e.g., using
fluent-plugin-rewrite-tag-filter) to drop any tags containing.or/characters.
- Strictly validate and filter incoming tags at the input layer (e.g., using
Impact
This vulnerability allows for Arbitrary File Write, which can be directly escalated to full Remote Code Execution (RCE).
An attacker could achieve RCE by overwriting critical system files, injecting executable plugins, or modifying configuration files.
The impact is Critical as it can lead to full system compromise without any authentication, depending on the Fluentd configuration and the privileges of the Fluentd process.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-44024 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.19.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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v1.19.3
Frequently Asked Questions
- What is CVE-2026-44024? CVE-2026-44024 is a critical-severity path traversal vulnerability in fluentd (rubygems), affecting versions <= 1.19.2. It is fixed in 1.19.3. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-44024? CVE-2026-44024 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of fluentd are affected by CVE-2026-44024? fluentd (rubygems) versions <= 1.19.2 is affected.
- Is there a fix for CVE-2026-44024? Yes. CVE-2026-44024 is fixed in 1.19.3. Upgrade to this version or later.
- Is CVE-2026-44024 exploitable, and should I be worried? Whether CVE-2026-44024 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44024 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44024? Upgrade
fluentdto 1.19.3 or later.