OSSN-0108: Multiple authentication vulnerabilities in Ceph

Summary

The latest Ceph releases of Ceph 20.2.4 and Ceph 19.2.6 patch four CVEs across several components (CVE-2025-30156, CVE-2026-39944, CVE-2026-50152 and CVE-2026-54330). All OpenStack services using CephX keyrings are affected. Ceph servers should be upgraded and their CephX keyrings should be rotated. The CephX keyrings used by OpenStack should be rotated only after Ceph client software on every OpenStack server is upgraded and then virtual machines need to be restarted or live migrated in order to load the new keyring.

Affected Services / Software

• Ceph (all versions prior to v20.2.4 or v19.2.6)

• OpenStack services with CephX keyrings (Nova, Cinder, Glance, Manila)

• Ceph RADOS Gateway (RGW), when used as an Object Store (Swift/S3) backend

Discussion

Any OpenStack service with a CephX keyring (Nova, Cinder, Glance, Manila) is at risk. Data-at-rest encryption is not affected by CVE-2025-30156 but is affected by CVE-2026-50152. Both are fixed by the update in addition to CVE-2026-39944 and CVE-2026-54330.

For an OpenStack cloud using RBD, RGW or NFS, this can be considered an internal vulnerability, potentially enabling an insider to escalate privilege. For example, a Nova guest using Cinder RBD does not have access to the CephX key or Ceph’s storage network; the Nova host has access to them but only an insider should have access to the Nova host. However, if an OpenStack tenant is using Manila with native CephFS (not with NFS-Ganesha), then those tenants could exploit these CVEs.

The hardcoded initialization vector means identical plaintexts produce identical ciphertexts. The missing HMAC allows CBC bit-flipping. An attacker who compromises any CephX entity (or obtains its shared secret from network traffic) can tamper with a ticket’s permissions without detection and forge credentials for privileged services.

The fix modifies Ceph to use AES256-CTS-HMAC-SHA384-192 (RFC 8009), a new CephX key type named aes256k. Both Ceph server and client packages must be upgraded to use it. If krbd (in place of librbd) or CephFS kernel mounts (in place of ceph-fuse or NFS-Ganesha) are used, the client also requires Linux kernel 7.0 or later. Upgrading the servers and rotating their keys to aes256k resolves the vulnerabilities; clients that have not yet been upgraded continue to authenticate with their existing aes keys in the meantime.

Recommended Actions

• Upgrade Ceph to a patched release and update Ceph clients on OpenStack.

• Re-create every CephX credential with the new aes256k cipher.

• Every OpenStack Nova guest must be live migrated (or restarted) to pick up the new CephX key.

OpenStack Service Keyrings (Nova, Cinder, Glance)

To use RBD with Nova, Cinder or Glance, these services should be configured with a Ceph user that uses a CephX key to authenticate to the Ceph cluster. This OSSN will refer to a single client.openstack key for simplicity but configurations with multiple keys are possible. Before rotating or replacing this key:

• The Ceph cluster should be using the new cipher for its internals. For example, the Ceph Monitor, OSD, RGW, MDS and other services should already have rotated their CephX keys so they use the new cipher.

• The Ceph cluster should allow connections from both the old and new cipher as confirmed by the following command:

  # ceph mon dump | grep allowed_ciphers
  auth_allowed_ciphers aes, aes256k
  

There are two strategies:

• Rotate: Use ceph auth rotate to rotate client.openstack.

• Replace: Create a new CephX key (e.g. client.openstack2), which uses the new cipher, and switch clients to use the new key.

If you are concerned about the time required to migrate Nova guests (so they start using the new key), then use the replacement strategy.

There is no immediate downtime when the credential is rotated but there is limited time to switch to the new credential. The client will continue to function until it tries to reauthenticate with the Ceph Monitors to get new tickets. During that time you can rotate and then restart clients incrementally. Knowing exactly how long you have to rotate the key for all clients can be difficult to predict given the distributed nature of Ceph but we believe it to be a matter of hours, not days.

Rather than be bound by the above, you can have complete control of when the old credential is no longer valid by having two valid credentials and rotating them on your own schedule and then disabling support for the old credential’s cipher.

The new CephX key must be distributed to every OpenStack node which connects to Ceph and be imported into libvirt prior migrating Nova guests to have them pick up the new key.

Manila with Native CephFS

With Manila, users create CephX keys for native CephFS share access. These keys are exposed to tenant VMs. To rotate, for each share:

1. Grant new share access (new CephX key with aes256k)

2. Remount the share using the new credentials

3. Revoke the old share access

All shares for a tenant must be covered. Partial rotation leaves the old CephX user and key valid for any shares not yet rotated.

Manila with NFS-Ganesha

The main NFS-Ganesha CephX key can be rotated and the service redeployed. Per-export CephX keys (created automatically per share) do not have a rotation mechanism yet. To rotate these, delete and recreate access rules for each share. This requires unmount/remount and is disruptive.

These per-export keys are internal to the Ceph cluster and not exposed to tenants. Operators can defer their rotation until Ceph provides a rotation mechanism if the risk is tolerable.

Enforcing the New Cipher

After all CephX keys have been rotated, enforce the new cipher:

ceph mon set auth_allowed_ciphers aes256k

Credits:

• Erin Shepherd (e43.eu)

• David Mohren (Clyso)

• Mark Nelson (Clyso)

Contacts / References

Author: John Fulton (Red Hat), Goutham Pacha Ravi (Red Hat), Sage McTaggart (IBM)

• This OSSN : https://docs.openstack.org/security-notes/OSSN-0108.html

• Mailing List : openstack-discuss@lists.openstack.org

• OpenStack Security : https://security.openstack.org/

• Ceph Advisory : https://ceph.io/en/news/blog/2026/v20-2-4-v19-2-6-combo-released/

• CVE-2025-30156 : https://nvd.nist.gov/vuln/detail/CVE-2025-30156

• CVE-2026-39944 : https://nvd.nist.gov/vuln/detail/CVE-2026-39944

• CVE-2026-50152 : https://nvd.nist.gov/vuln/detail/CVE-2026-50152

• CVE-2026-54330 : https://nvd.nist.gov/vuln/detail/CVE-2026-54330