CVE-2026-44024: Fluentd is Vulnerable to Remote Code Execution (RCE) via Arbitrary File Write in `${tag}` Placeholder

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 1.1%, percentile 65: FIRST’s model estimates a 1.1% chance of exploitation activity in the next 30 days, higher than 65% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes fluentd (RubyGems) <= 1.19.2, fixed in 1.19.3. Check your lockfile, including transitive dependencies.

What it is

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 outfile 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.

From the GitHub advisory

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 outfile 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.

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.

Patches v1.19.3

Weakness type: CWE-22, CWE-94.

Product: fluentd (RubyGems) · Assigned by: GitHub_M · Published: 2026-07-08

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.08% probability of exploitation activity in the next 30 days; percentile 65.

Timeline

• 2026-06-26 — GitHub-reviewed advisory GHSA-44hj-4m45-frj3 published (critical)
• 2026-07-08 — CVE record published by GitHub_M
• 2026-07-10 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-44hj-4m45-frj3 github.com
2. CVE.org record CVE-2026-44024 cve.org
3. NVD entry CVE-2026-44024 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical RubyGems advisories · Today’s Security Digest