OpenStack Cinder CVE-2026-93856

Requires an authenticated account with a project-scoped 'member' or 'reader' role in the target OpenStack deployment; the attacker then issues the Block Storage API v3.3 'List messages' call (GET /messages). No special or non-default configuration is needed - all Cinder deployments are affected out of the box. Exploitation is time-bounded by the message_ttl option (default 30 days), as only non-expired messages are exposed, and message_reap_interval (default 24 hours) governs cleanup. The practical limiting factor is that the response does not include project_id, so the attacker needs an independent means to correlate each leaked resource UUID to its owning project; disclosed data is restricted to resource UUIDs plus sanitized, by-design generic message strings (no integrity or availability impact).

This is a genuine but moderate-severity multi-tenant isolation flaw rather than a high-urgency emergency. The OpenStack VMT advisory (OSSA-2026-045) confirms all Cinder deployments are affected, and exploitation requires only a low-privilege authenticated tenant account (project-scoped 'member' or 'reader' role) issuing a single Block Storage API v3.3 'List messages' call - low attack complexity, network-reachable. No CVSS vector, EPSS score, KEV listing, or public POC was provided in the input, so probability-of-exploitation signals are entirely absent and cannot be weighed. The realistic impact is bounded: only non-expired user messages (sanitized, by-design generic strings) and resource UUIDs of other projects are leaked, and the advisory explicitly notes the response omits project_id, so an attacker must independently correlate each UUID to its owning project before the leak becomes actionable. There is no integrity or availability impact. Net: a confirmed cross-tenant confidentiality boundary break that matters for multi-tenant/public-cloud operators, but the limited data exposed and the required correlation step keep real-world risk in the medium band. No CVSS vector is present in the source data - the vector below is this analyst's independent assessment and should be verified against the OpenStack advisory/NVD once published.

A legitimate tenant user holding only a 'member' or 'reader' role in an OpenStack cloud calls the Block Storage v3.3 'List messages' endpoint (GET /v3/{project_id}/messages) and receives, alongside their own messages, the non-expired user messages and resource UUIDs belonging to other tenants' projects. The attacker harvests these cross-project UUIDs to map other tenants' resources, though they must separately correlate each UUID to a project since project_id is not returned. No public exploit code is identified; the attack is a single low-complexity authenticated API request.