CVE-2026-46448: 
NixOS vulnerability analysis and mitigation

CVE-2026-46448 is a scheduler hint injection vulnerability in OpenStack Nova, tracked under OSSA-2026-022, that allows authenticated users to bypass Placement resource claims and scheduling constraint enforcement. Reported by Erichen from the Institute of Computing Technology, Chinese Academy of Sciences, it was disclosed on June 16, 2026. Affected versions span Nova >=18.0.0 <31.3.1, >=32.0.0 <32.2.1, and >=33.0.0 <33.0.2. The NVD assigns a CVSS v3.1 score of 8.5 (High) with a changed scope, while GitHub Advisory rates it 5.4 (Moderate) with unchanged scope (OSS-Security, GitHub Advisory).

The root cause is classified under CWE-669 (Incorrect Resource Transfer Between Spheres) and CWE-1173 (Improper Use of Validation Framework): Nova's server create API fails to strip internal scheduler hints supplied by the user before passing them to the scheduler. An authenticated user can inject these internal hints into a server creation request, causing the resulting instance to be placed without a corresponding Placement allocation and bypassing constraints such as availability zone, host aggregate, and image trait restrictions. This is a network-accessible attack requiring only low privileges and no user interaction. The bug is tracked at the Launchpad issue tracker and patches are available on OpenDev review (OSS-Security, GitHub Advisory).

Successful exploitation allows an authenticated low-privileged user to create instances that lack Placement allocations, leading to compute node resource exhaustion as the scheduler loses accurate accounting of consumed resources. Attackers can also bypass availability zone, host aggregate, and image trait restrictions, potentially placing workloads on unauthorized hosts or in restricted zones. A particularly severe consequence is cross-tenant data persistence on NVMe devices after instance deletion, which could expose sensitive data from other tenants' previously deleted instances (OSS-Security, GitHub Advisory).

1. Authentication: Obtain valid OpenStack credentials with at least a low-privileged user role in a Nova deployment running an affected version (>=18.0.0 <31.3.1, >=32.0.0 <32.2.1, or >=33.0.0 <33.0.2).
2. Craft malicious server create request: Construct a Nova server create API request (POST to /v2.1/{project_id}/servers) that includes internal scheduler hints that would normally be stripped by the API layer — specifically hints that influence Placement allocation or scheduling constraints.
3. Inject scheduler hints: Include the crafted hint data in the os:scheduler_hints field of the request body, targeting internal hints that bypass availability zone, host aggregate, or image trait restrictions.
4. Submit request: Send the crafted API request to the Nova API endpoint. Due to the missing input stripping, the internal hints are passed through to the scheduler.
5. Achieve impact: The resulting instance is created without a Placement allocation, causing the compute node's resource accounting to be inaccurate. Repeat this process to exhaust compute node resources (denial of service) or to place instances on restricted hosts, potentially accessing residual data on NVMe devices from previously deleted tenant instances (OSS-Security, GitHub Advisory).

• Logs: Nova API logs showing server create requests with unexpected or internal os:scheduler_hints values not typical for normal tenant usage; Nova scheduler logs showing instances placed without corresponding Placement allocation records.
• Placement Service: Instances visible in Nova compute but absent from the Placement service's allocation records — detectable by querying GET /placement/allocations/{consumer_uuid} and finding no allocations for running instances.
• Resource Accounting: Compute nodes reporting higher-than-expected resource utilization relative to Placement's view of allocated resources, indicating untracked instances consuming capacity.
• Scheduling Anomalies: Instances appearing in availability zones, host aggregates, or on hosts that their project should not have access to, based on policy or aggregate metadata review.

Operators should upgrade OpenStack Nova to one of the patched versions: 31.3.1 (for the 18.0.0–31.x series), 32.2.1 (for the 32.x series), or 33.0.2 (for the 33.x series). Patches are available on OpenDev for all active release branches: 2025.1/epoxy (review 993604), 2025.2/flamingo (993603), 2026.1/gazpacho (993602), and 2026.2/hibiscus (993601). As a short-term workaround, restrict Nova API access to trusted authenticated users only and monitor for instances lacking Placement allocations (OSS-Security, GitHub Advisory).

The vulnerability was disclosed via the OpenStack Vulnerability Management Team through the oss-security mailing list by Goutham Pacha Ravi on June 16, 2026. Red Hat opened a Bugzilla tracking entry (Bug 2489379) and assigned it medium severity for their products. Ubuntu also issued updates addressing this CVE alongside other OpenStack components. Community discussion was noted on Bluesky shortly after disclosure, and the issue was picked up by standard vulnerability tracking feeds including VulDB and CVEfeed (OSS-Security, Red Hat Bugzilla).