MinIO vulnerable to Path Traversal via msgpack Body in `ReadMultiple` Storage-REST Endpoint

### 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-encoded traversal bypasses it. Sibling storage methods (`StatInfoFile`, `ReadFileHandler`, `ReadVersion`) validate their volume argument through `s.getVolDir(volume)`, which rejects `..`; `ReadMultiple` skips this call. The attacker sends `POST /minio/storage/{drivePath}/v63/rmpl` with a msgpack-encoded body carrying `../` sequences in the `Bucket` field. The server opens the resulting path via `os.OpenFile` with `O_RDONLY|O_NOATIME` and returns its contents in the msgpack response stream. **Impact by deployment:** - **Bare-metal with `User=minio` in the systemd unit** — the `O_NOATIME` ownership check bounds the read to files owned by the MinIO UID. Reachable secrets include TLS private keys, KMS/KES key material, systemd credentials, and data belonging to other tenants sharing the same UID on the host. Secrets leaked this way persist across cluster credential rotation. - **Containerized running as UID 0** (the historical default for the official Docker image, `docker-compose` examples, and Helm charts without `securityContext.runAsNonRoot`) — the primitive escalates to arbitrary host-filesystem disclosure: `/etc/shadow`, `/root/**`, Kubernetes service-account tokens, cloud-init metadata caches. **Affected components:** `cmd/storage-rest-server.go` (`ReadMultiple` handler), `cmd/xl-storage.go` (`xlStorage.ReadMultiple`). **CWE:** CWE-22 (Improper Limitation of a Pathname to a Restricted Directory — 'Path Traversal') **CVSS v4.0 Score:** 6.9 (Medium) **Vector:** `CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N` ### Affected Versions All MinIO releases from `RELEASE.2022-07-24T01-54-52Z` through the final release of the minio/minio open-source project, `RELEASE.2025-09-07T16-13-09Z`. The vulnerability was introduced in commit [`f939d1c18`](https://github.com/minio/minio/commit/f939d1c1831c71f4b1c14df6d9cd62b12ccce7a3) ("Independent Multipart Uploads", [PR #15346](https://github.com/minio/minio/pull/15346)), which added the `ReadMultiple` storage-REST endpoint as part of the multipart upload redesign. The first affected release is `RELEASE.2022-07-24T01-54-52Z`. ### Patches **Fixed in**: MinIO AIStor `RELEASE.2026-04-14T21-32-45Z` (recommended upgrade target). The fix — which removed the `ReadMultiple` handler, the corresponding storage-driver method, the msgpack datatypes, the REST-client wrapper, and the route registration — first shipped in **MinIO AIStor `RELEASE.2024-10-23T19-38-07Z`**. Every AIStor release from `RELEASE.2024-10-23T19-38-07Z` onward is unaffected; users should upgrade to `RELEASE.2026-04-14T21-32-45Z` or later to pick up the accumulated fixes and improvements shipped since. #### 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 | | -------- | ------------ | --------------------------------------------------------------------------- | | Linux | amd64 | [minio.fips](https://dl.min.io/aistor/minio/release/linux-amd64/minio.fips) | | Linux | arm64 | [minio.fips](https://dl.min.io/aistor/minio/release/linux-arm64/minio.fips) | #### Package Downloads | Format | Architecture | Download | | ------ | ------------ | ----------------------------------------------------------------------------------------------------------------------------------- | | DEB | amd64 | [minio_20260414213245.0.0_amd64.deb](https://dl.min.io/aistor/minio/release/linux-amd64/minio_20260414213245.0.0_amd64.deb) | | DEB | arm64 | [minio_20260414213245.0.0_arm64.deb](https://dl.min.io/aistor/minio/release/linux-arm64/minio_20260414213245.0.0_arm64.deb) | | RPM | amd64 | [minio-20260414213245.0.0-1.x86_64.rpm](https://dl.min.io/aistor/minio/release/linux-amd64/minio-20260414213245.0.0-1.x86_64.rpm) | | RPM | arm64 | [minio-20260414213245.0.0-1.aarch64.rpm](https://dl.min.io/aistor/minio/release/linux-arm64/minio-20260414213245.0.0-1.aarch64.rpm) | #### Container Images ```bash # Standard docker pull quay.io/minio/aistor/minio:RELEASE.2026-04-14T21-32-45Z podman pull quay.io/minio/aistor/minio:RELEASE.2026-04-14T21-32-45Z # FIPS docker pull quay.io/minio/aistor/minio:RELEASE.2026-04-14T21-32-45Z.fips podman pull quay.io/minio/aistor/minio:RELEASE.2026-04-14T21-32-45Z.fips ``` #### Homebrew (macOS) ```bash brew install minio/aistor/minio ``` ### Workarounds - [Users of the open-source `minio/minio` project should upgrade to MinIO AIStor `RELEASE.2026-04-14T21-32-45Z` or later.](https://docs.min.io/enterprise/aistor-object-store/upgrade-aistor-server/community-edition/) If upgrading is not immediately possible: - **Rotate the root credential and restrict who holds it.** The exploit requires a JWT signed with `MINIO_ROOT_PASSWORD`. Treat the root credential as the host-filesystem disclosure primitive that it is: rotate it after any suspected exposure, store it only in the secret manager that bootstraps the cluster, and do not hand it to applications or operators who only need object-level access. - **Do not run the MinIO container as UID 0.** Set `securityContext.runAsNonRoot: true` (and a non-zero `runAsUser`) in Kubernetes manifests, or add `--user` to `docker run`. This reduces the blast radius from arbitrary host-filesystem disclosure to MinIO-UID-owned files only. - **Restrict the internode storage-REST port at the network layer.** In distributed deployments, the storage-REST route is served on the same port as the S3 API by default. Where feasible, use `--internode-port` to expose internode traffic on a separate interface reachable only from other cluster peers, and block that interface from client networks. ### Credits - **Finders:** Discovered by Claude, Anthropic's AI assistant, and triaged by **Adrian Denkiewicz** at **Doyensec** in collaboration with **Anthropic Research**. ### Resources - Introducing commit: [`f939d1c18`](https://github.com/minio/minio/commit/f939d1c1831c71f4b1c14df6d9cd62b12ccce7a3) ([PR #15346](https://github.com/minio/minio/pull/15346)) - [CWE-22 — Improper Limitation of a Pathname to a Restricted Directory](https://cwe.mitre.org/data/definitions/22.html) - [CVE-2022-35919 — MinIO admin-authenticated path traversal in server-update endpoint (same class, different channel)](https://github.com/minio/minio/security/advisories/GHSA-gr9v-6pcm-rqvg) - [MinIO AIStor](https://min.io/aistor)

Quoted source text, attributed separately from HOL analysis.