GHSA-j9cw-hwqf-85w7
HIGHGHSA-j9cw-hwqf-85w7 is a high-severity (CVSS 7.5) CWE-409 vulnerability in fluentd. O3 Security confirms whether GHSA-j9cw-hwqf-85w7 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Fluentd is Vulnerable to Denial of Service (DoS) via Gzip Decompression Bomb in `in_http` and `in_forward`
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.
- 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-j9cw-hwqf-85w7.
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-j9cw-hwqf-85w7 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's in_http and in_forward plugins support receiving gzip-compressed data.
While Fluentd correctly enforces size limits on the incoming compressed payloads (e.g., via body_size_limit or chunk_size_limit), it was discovered that there is no limit enforced on the size of the decompressed data.
If a Fluentd instance is exposed to untrusted networks, an attacker can send a maliciously crafted, highly compressed payload. When Fluentd attempts to decompress this payload in memory, it will expand to an excessive size, completely bypassing the intended payload size limits.
Impact
This vulnerability allows for a Denial of Service (DoS) attack via memory exhaustion. The rapid memory consumption during decompression can easily lead to an Out-of-Memory kill of the Fluentd process by the operating system. This results in the disruption of all log collection and forwarding capabilities on the affected node.
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
9880forin_httpand24224forin_forward) 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
- Use a Reverse Proxy
- If developers must expose HTTP ingestion to external sources, place a robust reverse proxy (such as Nginx) in front of Fluentd. Configure the proxy to handle the gzip decompression and enforce strict limits on both compressed and uncompressed body sizes before passing the traffic to Fluentd.
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-j9cw-hwqf-85w7 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-j9cw-hwqf-85w7 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-j9cw-hwqf-85w7. 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-j9cw-hwqf-85w7 in your dependencies?
O3 detects GHSA-j9cw-hwqf-85w7 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.