Executive brief
OpenStack Nova, the component responsible for provisioning virtual machines, contains a flaw where users can bypass resource management controls. By injecting specific internal commands during server creation, an authenticated user can launch virtual machines that are not properly tracked by the system's resource manager. This can lead to physical server resource exhaustion, impacting service availability, and may result in sensitive data remaining on storage devices after a machine is deleted.
Technical details
A vulnerability in OpenStack Nova's server create API arises because the 'os:scheduler_hints' JSON schema allows additional properties and fails to strip internal-only sentinel values prefixed with '_nova_'. An authenticated attacker can inject the '_nova_check_type' hint set to 'rebuild', which tricks the 'request_is_rebuild' function in the scheduler into treating a new instance creation as a rebuild. This causes the scheduler to skip Placement API resource claims and bypass constraints like availability zones or host aggregates. Exploitation results in 'ghost' instances that consume physical CPU, memory, and disk without being tracked, potentially leading to host-level Denial of Service (DoS) and cross-tenant data persistence on NVMe devices. Patches have been released for versions 31.3.1, 32.2.1, and 33.0.2.
Affected products
- OpenStack Nova >=18.0.0 <31.3.1, >=32.0.0 <32.2.1, >=33.0.0 <33.0.2
Timeline
- 2026-05-05: disclosed: Bug reported to OpenStack Launchpad
- 2026-06-16: advisory: OSSA-2026-022 published
- 2026-06-16: patched: Fixes released across multiple branches