GitHub Security Advisory: GHSA-hv4r-mvr4-25vw
Package: github.com/minio/minio (GO)
Severity: HIGH (CVSS 8.2)
CWE: CWE-287: Improper Authentication
Vulnerable versions: >= 0.0.0[PII_REDACTED]5312-76913a9fd5c6, <= 0.0.0[PII_REDACTED]1848-7aac2a2c5b7c
Patched in: unpatched

Summary: MinIO has an Unauthenticated Object Write via Query-String Credential Signature Bypass in Unsigned-Trailer Uploads

Details:
### Impact

_What kind of vulnerability is it? Who is impacted?_

An authentication bypass vulnerability in MinIO's `STREAMING-UNSIGNED-PAYLOAD-TRAILER` code path
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.

`PutObjectHandler` and `PutObjectPartHandler` call `newUnsignedV4ChunkedReader` with a signature
verification gate based solely on the presence of the `Authorization` header:

```go
newUnsignedV4ChunkedReader(r, true, r.Header.Get(xhttp.Authorization) != "")
```

Meanwhile, `isPutActionAllowed` extracts credentials from either the `Authorization` header or the
`X-Amz-Credential` query parameter, and trusts whichever it finds. An attacker omits the
`Authorization` header and supplies credentials exclusively via the query string. The signature gate
evaluates to `false`, `doesSignatureMatch` is never called, and the request proceeds with the
permissions of the impersonated access key.

This affects `PutObjectHandler` (standard and tables/warehouse bucket paths) and
`PutObjectPartHandler` (multipart uploads).

**Affected components:** `cmd/object-handlers.go` (`PutObjectHandler`),
`cmd/object-multipart-handlers.go` (`PutObjectPartHandler`).

### Affected Versions

All MinIO releases through the final release of the minio/minio open-source project.

The vulnerability was introduced in commit
[`76913a9fd`](https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091)
("Signed trailers for signature v4", [PR #16484](https://github.com/minio/minio/pull/16484)),
which added `authTypeStreamingUnsignedTrailer` support. The first affected release is
`RELEASE.2023-05-18T00-05-36Z`.

### Patches

**Fixed in**: MinIO AIStor RELEASE.2026-04-11T03-20-12Z

#### Binary Downloads

| Platform | Architecture | Download                                                                    |
| -------- | ------------ | --------------------------------------------------------------------------- |
| Linux    | amd64        | [minio](https://dl.min.io/aistor/minio/release/linux-amd64/minio)           |
| Linux    | arm64        | [minio](https://dl.min.io/aistor/minio/release/linux-arm64/minio)           |
| macOS    | arm64        | [minio](https://dl.min.io/aistor/minio/release/darwin-arm64/minio)          |
| macOS    | amd64        | [minio](https://dl.min.io/aistor/minio/release/darwin-amd64/minio)          |
| Windows  | amd64        | [minio.exe](https://dl.min.io/aistor/minio/release/windows-amd64/minio.exe) |

#### FIPS Binaries

| Platform | Architecture | Download                                                                    |
| -------- | ------------ | --------------------------------------------------------------------------- |
| Lin