GHSA-44hj-4m45-frj3
CRITICALGHSA-44hj-4m45-frj3 is a critical-severity (CVSS 9.8) Path Traversal vulnerability in fluentd. O3 Security confirms whether GHSA-44hj-4m45-frj3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Fluentd is Vulnerable to Remote Code Execution (RCE) via Arbitrary File Write in `${tag}` Placeholder
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-44hj-4m45-frj3.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-44hj-4m45-frj3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 363,588 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
fluentdReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
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.
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
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | fluentd | all versions | 1.19.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fluentd. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update fluentd to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-44hj-4m45-frj3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-44hj-4m45-frj3 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-44hj-4m45-frj3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-44hj-4m45-frj3 in your dependencies?
O3 detects GHSA-44hj-4m45-frj3 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.