CVE-2026-44160 is a high-severity (CVSS 7.5) CWE-409 vulnerability in fluentd. A fix is available for fluentd — see the affected versions and patch details below.
Fluentd: 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 CVE-2026-44160.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-44160 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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 | 1.19.3bundle update fluentd --conservative |
Affected Products
fluentdfluentdDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fluentd, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fluentd to 1.19.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44160 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2026-44160 in your dependencies?
Find it across RubyGems, including transitive dependencies.