When multiple devices share resources and one of them is to be passed through to a guest, security of the entire system and of respective guests individually cannot really be guaranteed without knowing internals of any of the involved guests. Therefore such a configuration cannot really be security-supported, yet making that explicit was so far missing.
Resources the sharing of which is known to be problematic include, but are not limited to
- PCI Base Address Registers (BARs) of multiple devices mapping to the same page (4k on x86),
- INTx lines.
Weakness
The product does not properly control the allocation and maintenance of a limited resource.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Xen | Xen | - (including) | - (including) |
| Xen | Ubuntu | focal | * |
| Xen | Ubuntu | oracular | * |
| Xen | Ubuntu | plucky | * |
Potential Mitigations
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/147.html
- https://cwe.mitre.org/data/definitions/227.html
- https://cwe.mitre.org/data/definitions/492.html