MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads

{
  "id": "033f9bc6aa8a7f5cde89cb9ac6a58ba3c682512768bfc39d63081cf723394cf0",
  "url": "https://osv.dev/vulnerability/GHSA-9c4q-hq6p-c237",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads",
    "summary": "### Impact Two authentication bypass vulnerabilities in MinIO's `STREAMING-UNSIGNED-PAYLOAD-TRAILER` code path allow any user who knows a valid access key to write arbitrary objects to any bucket without knowing the secret key or providing a valid cryptographic signature. Any MinIO deployment is impacted. The attack requires only a valid access key (the well-known default `minioadmin`, or any key with WRITE permission on a bucket) and a target bucket name. There are two vulnerabilities: 1. Missing Signature Verification in PutObjectExtractHandler / Snowball (CWE-306) 2. Signature Verification Bypass via Query-String Credentials (CWE-287) **Vulnerability 1 — Missing signature verification in PutObjectExtractHandler (Snowball)** When `authTypeStreamingUnsignedTrailer` support was added (commit 76913a9fd, PR #16484), the new auth type was handled in `PutObjectHandler` and `PutObjectPartHandler` but was never added to `PutObjectExtractHandler`. The snowball auto-extract handler's `switch rAuthType` block has no case for `authTypeStreamingUnsignedTrailer`, so execution falls through with zero signature verification. The `isPutActionAllowed` call before the switch extracts the access key and checks IAM permissions, but does not verify the cryptographic signature. An attacker sends a PUT request with `X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER`, `X-Amz-Meta-Snowball-Auto-Extract: true`, and an `Authorization` header containing a valid access key with a completely fabri",
    "evidence": "osv:GHSA-9c4q-hq6p-c237",
    "products": [
      {
        "name": {
          "value": "github.com/minio/minio",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-9c4q-hq6p-c237",
      "aliases": [
        "CVE-2026-40344",
        "GHSA-9c4q-hq6p-c237",
        "GO-2026-5284"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L"
        },
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.0.0-20230506025312-76913a9fd5c6"
                },
                {
                  "last_affected": "0.0.0-20260212201848-7aac2a2c5b7c"
                }
              ]
            }
          ],
          "package": {
            "name": "github.com/minio/minio",
            "purl": "pkg:golang/github.com/minio/minio",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-9c4q-hq6p-c237/GHSA-9c4q-hq6p-c237.json"
          }
        }
      ],
      "modified": "2026-10-08T08:11:02.200052299Z",
      "provider": "osv",
      "references": [
        "https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-40344",
        "https://github.com/minio/minio/pull/16484",
        "https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091",
        "https://github.com/minio/minio"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-287",
          "CWE-306"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": "2026-04-22T01:16:05Z",
        "github_reviewed_at": "2026-04-14T00:04:45Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-40344",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 98765,
  "published_at": "2026-04-14T00:04:45+00:00"
}