Summary
fluent-plugin-s3 Vulnerable to Denial of Service (DoS) via Decompression Bomb in in_s3
The fluent-plugin-s3 plugin (specifically the in_s3 input plugin) supports reading and decompressing heavily compressed files (such as gzip, lzma2, and lzop) from Amazon S3.
It was discovered that the plugin read the entire decompressed payload into memory at once without enforcing a strict size limit.
If an attacker has sufficient permissions to upload files to the monitored S3 bucket, they can upload a maliciously crafted, highly compressed file.
When Fluentd attempts to decompress this file, it will expand to an excessive size and it will consume significant system resources.
Workarounds
If an immediate upgrade is not possible, mitigate the risk by applying strict IAM access controls:
- Restrict Bucket Access
- Ensure that write (PUT) access to the S3 bucket monitored by
in_s3is strictly limited to trusted services and administrators. Prevent any public or untrusted uploads to the S3 bucket.
- Ensure that write (PUT) access to the S3 bucket monitored by
Impact
This vulnerability allows for a Denial of Service (DoS) attack via memory exhaustion.
The rapid memory consumption during decompression can lead to an Out-of-Memory kill of the Fluentd process by the operating system,
This results in the disruption of all log collection on the affected node.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
CVE-2026-44162 has a CVSS score of 2.7 (Low). The vector is network-reachable, high 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 (1.8.5); 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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v1.8.5
Frequently Asked Questions
- What is CVE-2026-44162? CVE-2026-44162 is a low-severity allocation of resources without limits or throttling vulnerability in fluent-plugin-s3 (rubygems), affecting versions >= 0.7.0, <= 1.8.4. It is fixed in 1.8.5. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- How severe is CVE-2026-44162? CVE-2026-44162 has a CVSS score of 2.7 (Low). 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 fluent-plugin-s3 are affected by CVE-2026-44162? fluent-plugin-s3 (rubygems) versions >= 0.7.0, <= 1.8.4 is affected.
- Is there a fix for CVE-2026-44162? Yes. CVE-2026-44162 is fixed in 1.8.5. Upgrade to this version or later.
- Is CVE-2026-44162 exploitable, and should I be worried? Whether CVE-2026-44162 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-2026-44162 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-2026-44162? Upgrade
fluent-plugin-s3to 1.8.5 or later.