Improper verification of cryptographic signature vulnerability in Ceph RGW's SigV4 handler. The flaw is caused by RGW only verifying the validity of headers listed in X-Amz-SignedHeaders without checking whether additional unsigned x-amz- headers are present on the request. AWS S3 requires every x-amz- header to be signed and rejects requests carrying unsigned headers, but RGW does not enforce this check. An attacker holding only a presigned PUT URL can attach arbitrary x-amz- headers that RGW applies, granting more capabilities than the original signer intended, resulting in privilege escalation.

Use of a broken cryptographic algorithm vulnerability in Ceph RGW's STS session token handling. The STS tokens use the same unauthenticated AES-128-CBC handler as CephX (CVE-2025-30156) and share its lack of integrity protection. An attacker holding any valid STS token can use CBC bit-flipping to modify the token contents without detection, obtaining full RGW admin access. Unlike the CephX attack which requires access to the internal cluster network and a Ceph monitor, this attack is a self-contained modification of a token the attacker already holds, requiring only a single valid unprivileged STS token and STS to be enabled.