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

{
  "id": "2ec42c69e702a96a46e13cb2fdbb220cf4a19e00a0b453112ba215b86cc7dc79",
  "url": "https://osv.dev/vulnerability/BIT-minio-2026-40344",
  "method": "structured",
  "payload": {
    "kind": "withdrawal",
    "title": "MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads",
    "summary": "MinIO is a high-performance object storage system. Starting in 2023.05.18 and prior to 2026.04.11, an authentication bypass vulnerability in MinIO's Snowball auto-extract handler (`PutObjectExtractHandler`) allows 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. When `authTypeStreamingUnsignedTrailer` support was added, 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 fabricated signature. The request is accepted and the tar payload is extracted into the bucket. Users of the open-source minio/minio project should upgrade to MinIO AIStor 2026.04.11 or later. If upgrading is not i",
    "evidence": "osv:BIT-minio-2026-40344",
    "products": [
      {
        "name": {
          "value": "minio",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "BIT-minio-2026-40344",
      "aliases": [
        "BIT-minio-2026-40344"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "2023.05.18"
                }
              ]
            }
          ],
          "package": {
            "name": "minio",
            "purl": "pkg:bitnami/minio",
            "ecosystem": "Bitnami"
          },
          "severity": [
            {
              "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
            }
          ],
          "database_specific": {
            "source": "https://github.com/bitnami/vulndb/tree/main/data/minio/BIT-minio-2026-40344.json"
          }
        }
      ],
      "modified": "2026-10-08T08:11:02.807613373Z",
      "provider": "osv",
      "references": [
        "https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091",
        "https://github.com/minio/minio/pull/16484",
        "https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-40344"
      ],
      "provider_metadata": {
        "cpes": [
          "cpe:2.3:a:minio:minio:*:*:*:*:*:*:*:*",
          "cpe:2.3:a:minio:minio:*:*:*:*:*:go:*:*"
        ],
        "severity": "High"
      }
    },
    "related_cves": [],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 98795,
  "published_at": "2026-04-24T16:03:38.295+00:00"
}