High [CVE-2026-54330] RGW SigV4 verifier allows attachment of arbitrary unsigned x-amz-* headers leading to privilege escalation

Ceph is an open-source distributed storage platform providing object, block, and file storage.

In versions prior to 20.2.4 and 19.2.6, the Ceph Object Gateway (RGW) SigV4 handler does not reject requests that carry x-amz-* headers absent from the signed header set, allowing anyone holding a presigned URL to attach arbitrary unsigned x-amz-* headers that RGW will honor.

AWS S3 requires every x-amz-* header on a SigV4 request to be signed and rejects requests bearing additional unsigned headers, but RGW validates only the headers listed in X-Amz-SignedHeaders and ignores any extra ones, so they take effect without being covered by the signature.

By adding such headers to a presigned PUT URL, an attacker can grant themselves more capabilities than the URL's signer intended and escalate their privileges. This issue is fixed in versions 20.2.4 and 19.2.6.

A flaw was found in Ceph RGW's SigV4 signature verification handler. As a result, anyone holding a presigned PUT URL can attach arbitrary unsigned x-amz-* headers that RGW will honor, effectively escalating their privileges beyond what the original URL signer authorized.

This can lead to unauthorized access to and modification of S3 objects.

Affected products named by the advisory: Red Hat Ceph Storage 4; Red Hat Ceph Storage 5; Red Hat Ceph Storage 6; Red Hat Ceph Storage 7; and 2 more.