fix: guard SSE replication headers against injection (CVE-2026-34204)#23
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A regular client could supply X-Minio-Replication-Server-Side-Encryption-* headers in a PUT request, causing them to be stored as internal SSE metadata. This allowed injection of fake sealed key material, potentially bypassing SSE verification. Add a check in extractMetadataFromMime() to only accept headers in replicationToInternalHeaders when the request carries the X-Minio-Source-Replication-Request header, which is only set by MinIO's internal replication system.
sergiodj
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May 1, 2026
sergiodj
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Thanks, Will!
Claude has made a few suggestions when reviewing this PR, but I believe we can proceed with what we have and I can file a new PR later to improve on testing/etc.
This was referenced May 20, 2026
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Summary
extractMetadataFromMime()incmd/handler-utils.goaccepts any header listed insupportedHeaders, which includes the SSE replication headers (X-Minio-Replication-Server-Side-Encryption-Sealed-Key,-Seal-Algorithm,-Iv,X-Minio-Replication-Encrypted-Multipart, etc.). These get stored as internal object metadata viareplicationToInternalHeaders.A regular client can include these headers in a PUT request, injecting fake sealed key material into object metadata. This can cause the server to treat an unencrypted object as SSE-encrypted, or to use attacker-controlled key material — bypassing SSE verification.
Fix
Add a replication request guard at the top of the
supportedHeadersloop inextractMetadataFromMime(). Headers that map throughreplicationToInternalHeadersare only accepted when the request carriesX-Minio-Source-Replication-Request, which is set exclusively by MinIO's internal replication system.Non-replication requests that supply these headers will have them silently dropped.
Notes
/cc @sergiodj for review