CVE-2022-42333 in Xen
Summary
by MITRE • 03/21/2023
x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] To allow cachability control for HVM guests with passed through devices, an interface exists to explicitly override defaults which would otherwise be put in place. While not exposed to the affected guests themselves, the interface specifically exists for domains controlling such guests. This interface may therefore be used by not fully privileged entities, e.g. qemu running deprivileged in Dom0 or qemu running in a so called stub-domain. With this exposure it is an issue that - the number of the such controlled regions was unbounded (CVE-2022-42333), - installation and removal of such regions was not properly serialized (CVE-2022-42334).
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Analysis
by VulDB Data Team • 04/12/2023
The vulnerability described in CVE-2022-42333 represents a critical flaw in the x86 Hardware Virtual Machine (HVM) implementation within virtualization environments, specifically affecting how pinned cache attributes are managed for hardware pass-through devices. This issue stems from improper handling of cacheability control mechanisms that are designed to allow domain controllers to override default memory caching policies for HVM guests. The vulnerability occurs at the hypervisor level where the interface intended for privileged domain controllers to manage memory regions with specific cache attributes lacks proper boundary controls, creating a potential attack surface for entities with limited privileges.
The technical flaw manifests through an unbounded number of controlled memory regions that can be created through the exposed interface, which violates fundamental security principles of resource management and access control. This unbounded allocation capability enables malicious actors to exhaust system resources or potentially cause system instability through excessive memory mapping operations. The vulnerability specifically impacts the Xen hypervisor implementation where the interface for managing pinned cache attributes was not properly constrained, allowing unauthorized entities to create an unlimited number of memory regions that would otherwise be restricted. This misconfiguration creates a scenario where legitimate system operations can be disrupted or exploited through resource exhaustion attacks.
The operational impact of this vulnerability extends beyond simple resource exhaustion to encompass potential system stability and security implications. When combined with CVE-2022-42334, which addresses improper serialization of region installation and removal operations, the combined effect creates a more severe threat landscape. The lack of proper serialization means that concurrent operations on memory regions could lead to race conditions, memory corruption, or inconsistent cache states that might be exploited to escalate privileges or cause denial of service. Attackers could leverage these flaws to manipulate the hypervisor's memory management subsystem, potentially leading to complete system compromise or unauthorized access to guest virtual machines. The vulnerability particularly affects environments where qemu runs in privileged contexts such as Dom0 or stub domains, where the attack surface is already expanded due to elevated privileges.
Mitigation strategies for this vulnerability require immediate implementation of proper resource limits and access controls on the exposed interface. System administrators should implement strict quotas on the number of pinned memory regions that can be created and ensure proper serialization mechanisms are in place for region management operations. The fix should align with CWE-131 (Incorrect Calculation of Buffer Size) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) principles, addressing both the unbounded resource allocation and the lack of proper synchronization. Organizations should also consider implementing monitoring solutions to detect unusual patterns of memory region creation and removal operations. Additionally, the implementation should follow ATT&CK framework techniques T1059 (Command and Scripting Interpreter) and T1068 (Exploitation for Privilege Escalation) by ensuring proper input validation and access controls to prevent unauthorized use of the vulnerable interface. Regular security audits and penetration testing should verify that the implemented fixes properly address the root causes of both CVE-2022-42333 and CVE-2022-42334 vulnerabilities.