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.