MinIO is Vulnerable to SSE Metadata Injection via Replication Headers

Impact

What kind of vulnerability is it? Who is impacted?

A flaw in extractMetadataFromMime() allows any authenticated user with s3:PutObject permission to inject internal server-side encryption metadata into objects by sending crafted X-Minio-Replication-* headers on a normal PutObject request. The server unconditionally maps these headers to X-Minio-Internal-* encryption metadata without verifying that the request is a legitimate replication request. Objects written this way carry bogus encryption keys and become permanently unreadable through the S3 API.

Any authenticated user or service with s3:PutObject permission on any bucket can make objects permanently unreadable by injecting fake SSE encryption metadata. The attacker sends a standard PutObject request with X-Minio-Replication-Server-Side-Encryption-* headers but without the X-Minio-Source-Replication-Request header that marks legitimate replication traffic. The server maps these headers to internal encryption metadata (X-Minio-Internal-Server-Side-Encryption-Sealed-Key, etc.), causing all subsequent GetObject and HeadObject calls to treat the object as encrypted with keys that do not exist.

This is a targeted denial-of-service vulnerability. An attacker can selectively corrupt individual objects or entire buckets. The ReplicateObjectAction IAM permission is never checked because the request is a normal PutObject, not a replication request.

Affected component: cmd/handler-utils.go, function extractMetadataFromMime().

Affected Versions

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

The vulnerability was introduced in commit 468a9fae83e965ecefa1c1fdc2fc57b84ece95b0 ("Enable replication of SSE-C objects", PR #19107, 2024-03-28). The first affected release is RELEASE.2024-03-30T09-41-56Z.

Patches

Fixed in: MinIO AIStor RELEASE.2026-03-26T21-24-40Z

Binary Downloads

| Platform | Architecture | Download | | -------- | ------------ | -------- | | Linux | amd64 | minio | | Linux | arm64 | minio | | macOS | arm64 | minio | | macOS | amd64 | minio | | Windows | amd64 | minio.exe |

FIPS Binaries

| Platform | Architecture | Download | | -------- | ------------ | -------- | | Linux | amd64 | minio.fips | | Linux | arm64 | minio.fips |

Package Downloads

| Format | Architecture | Download | | ------ | ------------ | -------- | | DEB | amd64 | minio_20260326212440.0.0_amd64.deb | | DEB | arm64 | minio_20260326212440.0.0_arm64.deb | | RPM | amd64 | minio-20260326212440.0.0-1.x86_64.rpm | | RPM | arm64 | minio-20260326212440.0.0-1.aarch64.rpm |

Container Images

# Standard
docker pull quay.io/minio/aistor/minio:RELEASE.2026-03-26T21-24-40Z
podman pull quay.io/minio/aistor/minio:RELEASE.2026-03-26T21-24-40Z

# FIPS
docker pull quay.io/minio/aistor/minio:RELEASE.2026-03-26T21-24-40Z.fips
podman pull quay.io/minio/aistor/minio:RELEASE.2026-03-26T21-24-40Z.fips

Homebrew (macOS)

brew install minio/aistor/minio

Workarounds

Users of the open-source minio/minio project should upgrade to MinIO AIStor RELEASE.2026-03-26T21-24-40Z or later.

If upgrading is not immediately possible:

• Restrict replication headers at a reverse proxy / load balancer. Drop or reject any request containing X-Minio-Replication-Server-Side-Encryption-* headers that does not also carry X-Minio-Source-Replication-Request. This blocks the injection path without modifying the server.

• Audit IAM policies. Limit s3:PutObject grants to trusted principals. While this reduces the attack surface, it does not eliminate the vulnerability since any authorized user can exploit it.

References

• Introducing commit: 468a9fae8 (PR #19107)
• MinIO AIStor