CVE-2026-39944
HighCVSS 8.8Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
Ceph versions prior to 20.2.4 and 19.2.6, in RADOS Gateway (RGW), protect STS session tokens with AES-128-CBC without message authentication, allowing an attacker holding a valid STS token to tamper with it undetected and escalate to full RGW administrative access.
Risk Assessment
An attacker can modify their own token, setting is_admin to true, which triggers a global administrative override and bypasses all capability checks. This could lead to full compromise of the Ceph cluster.
Recommendation
Upgrade Ceph to version 20.2.4 or 19.2.6. Consider disabling STS if not required.
Original NVD description (English source)
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 RADOS Gateway (RGW) protects STS session tokens with an AES-128-CBC handler that provides no message authentication, allowing an attacker who holds any valid STS token to tamper with it undetected and escalate to full RGW administrative access. Because the ciphertext is unauthenticated, the attacker can perform a CBC bit-flip on the acct_type, perm_type, and is_admin fields of their own token, and a forged is_admin value triggers a global administrative override that bypasses all capability checks. The attack is reachable remotely over the RGW S3 endpoint and is a self-contained modification of a token the attacker already possesses, requiring no encryption oracle and no network observation. It requires only a single valid STS token, which need not carry any elevated privileges, with STS enabled. This issue is fixed in versions 20.2.4 and 19.2.6.