CVE-2026-46448: OpenStack Nova Server Create API Placement Allocation Bypass

Technical summary

CVE-2026-46448 stems from insufficient input sanitization in Nova's server create API endpoint. When a user submits a CreateServer request with certain hint parameters, the API does not strip or validate these hints correctly. The absence of proper Placement allocation on the resulting instance can cause the Nova scheduler to lose track of resource assignments, potentially leading to inconsistent state between the compute node and the placement database. This breach of the placement contract affects resource accounting and scheduling decisions downstream.

Business impact

Affected cloud operators may experience resource tracking inconsistencies that complicate billing, capacity planning, and fair allocation among tenants. Instances created via the vulnerable API carry opaque resource assignments, making it difficult for the platform to enforce quota limits and predict future scheduling conflicts. In multi-tenant environments, this can degrade service quality and create audit complications when correlating resource usage to customer charges.

Affected systems

OpenStack Nova installations prior to version 33.0.2 are vulnerable. This includes all deployments using Nova for compute orchestration, regardless of deployment model (TripleO, Kolla, or standalone). The issue is triggered only when the server create API is called, so actively used cloud environments with frequent instance provisioning face the highest exposure.

Exploitability

The vulnerability requires valid Nova API credentials (authenticated access), making it unavailable to unauthenticated attackers. The API call is straightforward and requires no special conditions or user interaction beyond a standard CreateServer request with crafted hint parameters. The low complexity barrier and network accessibility mean that any authenticated tenant or operator can trigger the issue, making it a persistent risk in multi-tenant clouds where user isolation is expected.

Remediation

Upgrade OpenStack Nova to version 33.0.2 or later. This patch version corrects the hint-stripping logic in the server create API, ensuring that Placement allocation is properly established for all new instances. Organizations should verify the patch version against the official OpenStack release notes and test in a non-production environment before rolling out to production clusters.

Patch guidance

Deploy Nova 33.0.2 as soon as feasible. The patch is a point release that addresses input validation without introducing breaking changes. Plan the upgrade during a maintenance window and perform a rolling restart of Nova API and conductor services to apply the fix. Verify that newly created instances report correct Placement allocations via the Placement API after the upgrade. No database schema changes are required.

Detection guidance

Monitor for instances created with missing or malformed Placement allocation records. Query the Placement API to identify instances lacking resource provider allocations that should have been assigned. Review Nova API audit logs for CreateServer calls containing suspicious or unusual hint parameters. Consider implementing automated checks that validate Placement allocation integrity for all running instances, flagging those without proper resource tracking as potential indicators of exploitation.

Why prioritize this

Although the CVSS score of 5.4 is moderate, the vulnerability affects core cloud infrastructure stability and resource accountability. In a cloud with hundreds or thousands of instances, resource tracking inconsistencies compound and become difficult to remediate retroactively. The low barrier to exploitation via authenticated access and the broad impact on scheduling and billing make this a priority for operators managing production multi-tenant environments, even if critical data breaches are not the primary concern.

Risk score, explained

The CVSS 3.1 score of 5.4 (MEDIUM) reflects network accessibility, low attack complexity, and the requirement for local authentication. The score accounts for partial confidentiality and availability impact (information disclosure through resource state inconsistency and degraded scheduling), but no integrity impact. The moderate rating appropriately weighs the operational disruption risk against the lack of data breach or system compromise potential.

Frequently asked questions