MinIO vulnerable to Path Traversal via msgpack Body in `ReadMultiple` Storage-REST Endpoint
Date: 2026-05
Affected: go/github.com/minio/minio
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-42600
CWE: CWE-22
CVSS: 4.9 (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N)

### Impact _What kind of vulnerability is it? Who is impacted?_ A path traversal vulnerability in MinIO's `ReadMultiple` internode storage-REST endpoint allows a caller holding the cluster root JWT to read files from outside the configured drive roots, bounded only by the MinIO process UID. Distributed-erasure (multi-node) MinIO deployments are impacted. Single-node standalone deployments do not register the route and are not affected. The attack requires an HS512 JWT signed with `MINIO_ROOT_PASSWORD` and carrying `accessKey = MINIO_ROOT_USER` — the same secret every peer in the cluster holds to authenticate internode traffic, so a compromised peer or any actor in possession of the root credential can mint one. The `ReadMultiple` handler (`cmd/storage-rest-server.go`) decodes a msgpack `ReadMultipleReq` body containing `Bucket`, `Prefix`, and `Files` fields and forwards them to `xlStorage.ReadMultiple` (`cmd/xl-storage.go`) without validation: ```go volumeDir := pathJoin(s.drivePath, req.Bucket) // traversal resolves here for _, f := range req.Files { fullPath := pathJoin(volumeDir, req.Prefix, f) data, mt, err = s.readAllDataWithDMTime(ctx, req.Bucket, volumeDir, fullPath) } ``` `pathJoin` calls `path.Clean`, which resolves `..` components and produces an absolute path anywhere on the filesystem — it is not a root jail. The global `setRequestValidityMiddleware` rejects `..` in `r.URL.Path` and `r.Form` but does not inspect request bodies, so msgpack-en


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