CVE-2026-40344: Github.com/minio/minio MinIO Has An Unauthenticated Object Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9c4q-hq6p-c237",
  "modified" : "2026-05-05T15:43:25Z",
  "published" : "2026-04-14T00:04:45Z",
  "aliases" : [ "CVE-2026-40344" ],
  "summary" : "MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads",
  "details" : "### Impact\n\nTwo authentication bypass vulnerabilities in MinIO's `STREAMING-UNSIGNED-PAYLOAD-TRAILER` code path\nallow any user who knows a valid access key to write arbitrary objects to any bucket without knowing\nthe secret key or providing a valid cryptographic signature.\n\nAny MinIO deployment is impacted. The attack requires only a valid access key (the well-known default\n`minioadmin`, or any key with WRITE permission on a bucket) and a target bucket name.\n\nThere are two vulnerabilities:\n\n1. Missing Signature Verification in PutObjectExtractHandler / Snowball (CWE-306)\n2. Signature Verification Bypass via Query-String Credentials (CWE-287)\n\n**Vulnerability 1 — Missing signature verification in PutObjectExtractHandler (Snowball)**\n\nWhen `authTypeStreamingUnsignedTrailer` support was added (commit 76913a9fd, PR #16484), the new auth\ntype was handled in `PutObjectHandler` and `PutObjectPartHandler` but was never added to\n`PutObjectExtractHandler`. The snowball auto-extract handler's `switch rAuthType` block has no case for\n`authTypeStreamingUnsignedTrailer`, so execution falls through with zero signature verification. The\n`isPutActionAllowed` call before the switch extracts the access key and checks IAM permissions, but\ndoes not verify the cryptographic signature.\n\nAn attacker sends a PUT request with `X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER`,\n`X-Amz-Meta-Snowball-Auto-Extract: true`, and an `Authorization` header containing a valid access key\nwith a completely fabricated signature. The request is accepted and the tar payload is extracted into\nthe bucket.\n\n**Affected component:** `cmd/object-handlers.go`, function `PutObjectExtractHandler`.\n\n**Vulnerability 2 — Signature verification bypass via query-string credentials**\n\n`PutObjectHandler` and `PutObjectPartHandler` call `newUnsignedV4ChunkedReader` with a signature\nverification gate based solely on the presence of the `Authorization` header:\n\n```go\nnewUnsignedV4ChunkedReader(r, true, r.Header.Get(xhttp.Authorization) != \"\")\n```\n\nMeanwhile, `isPutActionAllowed` extracts credentials from either the `Authorization` header or the\n`X-Amz-Credential` query parameter, and trusts whichever it finds. An attacker omits the\n`Authorization` header and supplies credentials exclusively via the query string. The signature gate\nevaluates to `false`, `doesSignatureMatch` is never called, and the request proceeds with the\npermissions of the impersonated access key.\n\n**Affected components:** `cmd/object-handlers.go` (`PutObjectHandler`),\n`cmd/object-multipart-handlers.go` (`PutObjectPartHandler`).\n\n**CVSS v4.0 Score:** 8.8 (High)\n\n**Vector:** `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`\n\n**CWE:** CWE-306 (Missing Authentication for Critical Function), CWE-287 (Improper Authentication)\n\n### Affected Versions\n\nAll MinIO releases through the final release of the minio/minio open-source project.\n\nBoth vulnerabilities were introduced in commit\n[`76913a9fd`](https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091)\n(\"Signed trailers for signature v4\", [PR #16484](https://github.com/minio/minio/pull/16484)),\nwhich added `authTypeStreamingUnsignedTrailer` support. The first affected release is\n`RELEASE.2023-05-18T00-05-36Z`.\n\n### Patches\n\n**Fixed in**: MinIO AIStor RELEASE.2026-04-11T03-20-12Z\n\n#### Binary Downloads\n\n| Platform | Architecture | Download                                                                    |\n| -------- | ------------ | --------------------------------------------------------------------------- |\n| Linux    | amd64        | [minio](https://dl.min.io/aistor/minio/release/linux-amd64/minio)           |\n| Linux    | arm64        | [minio](https://dl.min.io/aistor/minio/release/linux-arm64/minio)           |\n| macOS    | arm64        | [minio](https://dl.min.io/aistor/minio/release/darwin-arm64/minio)          |\n| macOS    | amd64        | [minio](https://dl.min.io/aistor/minio/release/darwin-amd64/minio)          |\n| Windows  | amd64        | [minio.exe](https://dl.min.io/aistor/minio/release/windows-amd64/minio.exe) |\n\n#### FIPS Binaries\n\n| Platform | Architecture | Download                                                                    |\n| -------- | ------------ | --------------------------------------------------------------------------- |\n| Linux    | amd64        | [minio.fips](https://dl.min.io/aistor/minio/release/linux-amd64/minio.fips) |\n| Linux    | arm64        | [minio.fips](https://dl.min.io/aistor/minio/release/linux-arm64/minio.fips) |\n\n#### Package Downloads\n\n| Format | Architecture | Download                                                                                                                            |\n| ------ | ------------ | ----------------------------------------------------------------------------------------------------------------------------------- |\n| DEB    | amd64        | [minio_20260411032012.0.0_amd64.deb](https://dl.min.io/aistor/minio/release/linux-amd64/minio_20260411032012.0.0_amd64.deb)         |\n| DEB    | arm64        | [minio_20260411032012.0.0_arm64.deb](https://dl.min.io/aistor/minio/release/linux-arm64/minio_20260411032012.0.0_arm64.deb)         |\n| RPM    | amd64        | [minio-20260411032012.0.0-1.x86_64.rpm](https://dl.min.io/aistor/minio/release/linux-amd64/minio-20260411032012.0.0-1.x86_64.rpm)   |\n| RPM    | arm64        | [minio-20260411032012.0.0-1.aarch64.rpm](https://dl.min.io/aistor/minio/release/linux-arm64/minio-20260411032012.0.0-1.aarch64.rpm) |\n\n#### Container Images\n\n```bash\n# Standard\ndocker pull quay.io/minio/aistor/minio:RELEASE.2026-04-11T03-20-12Z\npodman pull quay.io/minio/aistor/minio:RELEASE.2026-04-11T03-20-12Z\n\n# FIPS\ndocker pull quay.io/minio/aistor/minio:RELEASE.2026-04-11T03-20-12Z.fips\npodman pull quay.io/minio/aistor/minio:RELEASE.2026-04-11T03-20-12Z.fips\n```\n\n#### Homebrew (macOS)\n\n```bash\nbrew install minio/aistor/minio\n```\n\n### Workarounds\n\n- [Users of the open-source `minio/minio` project should upgrade to MinIO AIStor `RELEASE.2026-04-11T03-20-12Z` or later.](https://docs.min.io/enterprise/aistor-object-store/upgrade-aistor-server/community-edition/)\n\nIf upgrading is not immediately possible:\n\n- **Block unsigned-trailer requests at the load balancer.** Reject any request containing\n  `X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER` at the reverse proxy or WAF layer.\n  Clients can use `STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER` (the signed variant) instead.\n\n- **Restrict WRITE permissions.** Limit `s3:PutObject` grants to trusted principals. While this\n  reduces the attack surface, it does not eliminate the vulnerability since any user with WRITE\n  permission can exploit it with only their access key.\n\n### Credits\n\n- **Finder:** Arvin Shivram of Brutecat Security ([@ddd](https://github.com/ddd))\n\n### References\n\n- Introducing commit: [`76913a9fd`](https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091) ([PR #16484](https://github.com/minio/minio/pull/16484))\n- [MinIO AIStor](https://min.io/aistor)",
  "severity" : [ {
    "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" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/minio/minio"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.0.0-20230506025312-76913a9fd5c6"
      }, {
        "last_affected" : "0.0.0-20260212201848-7aac2a2c5b7c"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40344"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/minio/minio/pull/16484"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/minio/minio"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-287", "CWE-306" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-14T00:04:45Z",
    "nvd_published_at" : "2026-04-22T01:16:05Z"
  }
}