CVE-2026-39944 Ceph: CephX AES Authentication error
Attackers with valid STS tokens can tamper with unencrypted AES-CBC fields to gain full administrative access to Ceph RADOS Gateway.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39944?
CVE-2026-39944 is a high-severity vulnerability in ceph, published on 27 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Weakness: CWE-327
Which versions are affected by CVE-2026-39944?
1 open source package ship an affected version, including ceph.
| Package | Affected | Fixed in |
|---|---|---|
ceph Bitnami | From 19.0.0 | 19.2.6, 20.2.4 |
How do I fix CVE-2026-39944?
Upgrade ceph to a fixed version for your release line: 19.2.6 or 20.2.4.
Is CVE-2026-39944 being exploited?
There is no known exploitation of CVE-2026-39944 in the wild and no public exploit code.
Sources
Also known as BIT-ceph-2026-39944, DEBIAN-CVE-2026-39944, ECHO-81df-cb66-3def, GHSA-j73r-qrgx-jvq2, MINI-3qph-pgr9-fc22, MINI-x459-rwph-mh2j and 1 more.