Summary
Fluentd is Vulnerable to Denial of Service (DoS) via Gzip Decompression Bomb in inhttp and inforward
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.
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.
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.
CVE-2026-44160 has a CVSS score of 7.5 (High). 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-2026-44160? CVE-2026-44160 is a high-severity security vulnerability in fluentd (rubygems), affecting versions <= 1.19.2. It is fixed in 1.19.3.
- How severe is CVE-2026-44160? CVE-2026-44160 has a CVSS score of 7.5 (High). 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-2026-44160? fluentd (rubygems) versions <= 1.19.2 is affected.
- Is there a fix for CVE-2026-44160? Yes. CVE-2026-44160 is fixed in 1.19.3. Upgrade to this version or later.
- Is CVE-2026-44160 exploitable, and should I be worried? Whether CVE-2026-44160 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-2026-44160 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-2026-44160? Upgrade
fluentdto 1.19.3 or later.