Executive brief
Ceph is an open-source distributed storage system that manages large-scale data across multiple servers. The RADOS Gateway (RGW) component, which provides S3-compatible object storage access, uses weak encryption for session tokens. An attacker with any valid token can manipulate it to gain full administrative privileges, potentially accessing or modifying all stored data and administrative settings without needing to break encryption or steal credentials.
Technical details
The vulnerability is a cryptographic authentication bypass in Ceph's RADOS Gateway STS (Secure Token Service) implementation. RGW encrypts session tokens using AES-128-CBC without message authentication codes (MAC), allowing unauthenticated ciphertext modification. An attacker holding any valid STS token can perform CBC bit-flip attacks to tamper with the acct_type, perm_type, and is_admin fields. Flipping the is_admin bit triggers a global administrative override that bypasses all capability checks. The attack requires only a single valid STS token (which need not be privileged), is remotely exploitable via the S3 endpoint, and requires no encryption oracle or network observation. STS must be enabled and the attacker must have network access to the RGW S3 endpoint. Patches are available in versions 20.2.4 and 19.2.6.
Affected products
- Ceph Ceph prior to 20.2.4 and prior to 19.2.6
Timeline
- 2026-08-28: disclosed
- 2026-08-18: patched: Patches released in versions 19.2.6 and 20.2.4