Ceph up to 19.2.5/20.2.3 RADOS Gateway acct_type/perm_type/is_admin privileges management

Summaryinfo

A vulnerability marked as very critical has been reported in Ceph up to 19.2.5/20.2.3. Affected by this vulnerability is an unknown functionality of the component RADOS Gateway. The manipulation of the argument acct_type/perm_type/is_admin leads to privileges management. This vulnerability is uniquely identified as CVE-2026-39944. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Ceph up to 19.2.5/20.2.3. This issue affects an unknown code of the component RADOS Gateway. The manipulation of the argument acct_type/perm_type/is_admin with an unknown input leads to a privileges management vulnerability. Using CWE to declare the problem leads to CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-39944 since 04/08/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/28/2026). The attack technique deployed by this issue is T1068 according to MITRE ATT&CK.

Upgrading to version 19.2.6 or 20.2.4 eliminates this vulnerability.

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Productinfo

Name

• Ceph

Version

• 19.2.0
• 19.2.1
• 19.2.2
• 19.2.3
• 19.2.4
• 19.2.5
• 20.2.0
• 20.2.1
• 20.2.2
• 20.2.3

Website

• Product: https://github.com/ceph/ceph/

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