CVE-2026-44162: Fluent plugin s3 Denial of Service Vulnerability

LOW
Advisory Identifier: GHSA-xv9w-7v6q-hpjh
Share
CVSS 2.7
CWE-770
Published
Advisory Summary

CVE-2026-44162 is a LOW (CVSS 2.7) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Fluent plugin s3 libraries in the RubyGems ecosystem. The issue involves fluent-plugin-s3 vulnerable to denial of service (dos) via decompression bomb in `in_s3`. Remediation is available by upgrading affected packages to version 1.8.5.

CVE-2026-44162 at a Glance

CVE Identifier CVE-2026-44162
GHSA Identifier GHSA-xv9w-7v6q-hpjh
Severity LOW
CVSS v3.1 Base Score 2.7
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Fluent plugin s3
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 2.7

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required High (PR:H)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-44162

To remediate this vulnerability, upgrade all affected Fluent plugin s3 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

fluent-plugin-s3 fixed: 1.8.5 
Upgrade fluent-plugin-s3 to 1.8.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for fluent-plugin-s3

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-44162, inspect your project dependencies for Fluent plugin s3:

inspect dependencies for fluent-plugin-s3

Analyze the terminal output to locate any version of Fluent plugin s3 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.8.5), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Fluent plugin s3, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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. ### 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. ### Patches v1.8.5 ### Workarounds If an immediate upgrade is not possible, mitigate the risk by applying strict IAM access controls: 1. Restrict Bucket Access * Ensure that write (PUT) access to the S3 bucket monitored by `in_s3` is strictly limited to trusted services and administrators. Prevent any public or untrusted uploads to the S3 bucket.

CVE-2026-44162 Affected Fluent plugin s3 Versions

1 component(s)
Fixed Versions:
1.8.5
Product / Package Ecosystem Affected Versions Fixed Version
fluent-plugin-s3
gem/fluent-plugin-s3
RubyGems
≥ 0.7.0
< 1.8.5
1.8.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fluent/fluent-plugin-s3/security/advisories/GHSA-xv9w-7v6q-hpjh
Security Fix Commit FIX COMMIT
https://github.com/fluent/fluent-plugin-s3/commit/e085aee001d15bcc4bd073507e74075e30550fd0
Fluent plugin s3 Source Repository REPOSITORY
https://github.com/fluent/fluent-plugin-s3

Frequently Asked Questions

What is CVE-2026-44162?
CVE-2026-44162 is a security vulnerability in Fluent plugin s3 involving fluent-plugin-s3 Vulnerable to Denial of Service (DoS) via Decompression Bomb in `in_s3` under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Fluent plugin s3 versions are affected?
Affected versions include releases prior to 1.8.5 across affected packages: fluent-plugin-s3.
What version fixes CVE-2026-44162?
Upgrading to 1.8.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is fluent-plugin-s3 affected?
Yes, fluent-plugin-s3 is affected in releases prior to 1.8.5. Upgrade your dependency to 1.8.5 or later.
What is the CVSS score of CVE-2026-44162?
CVE-2026-44162 has a CVSS v3.1 base score of 2.7 (LOW) with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-44162?
CVE-2026-44162 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check RubyGems dependencies for CVE-2026-44162?
Run the dependency tree command: 'inspect dependencies for fluent-plugin-s3'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xv9w-7v6q-hpjh",
  "modified" : "2026-06-26T17:02:19Z",
  "published" : "2026-06-26T17:02:19Z",
  "aliases" : [ "CVE-2026-44162" ],
  "summary" : "fluent-plugin-s3 Vulnerable to Denial of Service (DoS) via Decompression Bomb in `in_s3`",
  "details" : "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. \nIt was discovered that the plugin read the entire decompressed payload into memory at once without enforcing a strict size limit.\n\nIf an attacker has sufficient permissions to upload files to the monitored S3 bucket, they can upload a maliciously crafted, highly compressed file.\nWhen Fluentd attempts to decompress this file, it will expand to an excessive size and it will consume significant system resources.\n\n### Impact\nThis vulnerability allows for a **Denial of Service (DoS)** attack via memory exhaustion. \nThe rapid memory consumption during decompression can lead to an Out-of-Memory kill of the Fluentd process by the operating system, \nThis results in the disruption of all log collection on the affected node.\n\n### Patches\nv1.8.5\n\n### Workarounds\nIf an immediate upgrade is not possible, mitigate the risk by applying strict IAM access controls:\n\n1. Restrict Bucket Access\n   * Ensure that write (PUT) access to the S3 bucket monitored by `in_s3` is strictly limited to trusted services and administrators. Prevent any public or untrusted uploads to the S3 bucket.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "fluent-plugin-s3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.7.0"
      }, {
        "fixed" : "1.8.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.8.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fluent/fluent-plugin-s3/security/advisories/GHSA-xv9w-7v6q-hpjh"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fluent/fluent-plugin-s3/commit/e085aee001d15bcc4bd073507e74075e30550fd0"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fluent/fluent-plugin-s3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T17:02:19Z",
    "nvd_published_at" : null
  }
}