Executive brief
Apache CloudStack is an open-source cloud orchestration platform used to manage virtual infrastructure. An authenticated tenant can upload VM templates pointing to attacker-controlled metalink files, allowing the CloudStack infrastructure to fetch and execute malicious content. This enables remote code execution as root on the underlying KVM hypervisor, affecting other tenants' virtual machines and giving attackers complete control over the compute infrastructure.
Technical details
The vulnerability is a Server-Side Request Forgery (SSRF) combined with remote code execution via improper validation of metalink file URLs. When a CloudStack user registers a VM template with directDownload=true and a URL pointing to a .metalink XML file, the management server fetches the metalink and extracts inner URLs without validating them against the configured scheme allowlist. The KVM agent then downloads content from these unvalidated URLs, which can point to internal services (SSRF) or be used to inject arbitrary commands. An authenticated user with the default User role can trigger this via the public CloudStack API, achieving cross-tenant root code execution on KVM hypervisors. The vulnerability affects CloudStack versions 4.14.0.0 through 4.20.3.0 and 4.21.0.0 through 4.22.1.0; patches are available in 4.20.3.1, 4.22.1.1, and later.
Affected products
- Apache CloudStack 4.14.0.0 through 4.20.3.0, 4.21.0.0 through 4.22.1.0
Timeline
- 2026-08-21: disclosed
- 2026: patched: Fixed in versions 4.20.3.1, 4.22.1.1, and later