CVE-2018-19962 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.11.x on AMD x86 platforms, possibly allowing guest OS users to gain host OS privileges because small IOMMU mappings are unsafely combined into larger ones.
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Analysis
by VulDB Data Team • 06/13/2023
The vulnerability identified as CVE-2018-19962 represents a critical security flaw in the Xen hypervisor affecting versions through 4.11.x on AMD x86 platforms. This issue stems from improper handling of IOMMU (Input-Output Memory Management Unit) mappings within the virtualization environment, creating a potential privilege escalation pathway from guest operating systems to the underlying host system. The flaw specifically manifests when the hypervisor attempts to optimize memory mapping by combining smaller IOMMU mappings into larger ones, a process that introduces security vulnerabilities through unsafe consolidation operations.
The technical root cause of this vulnerability lies in the IOMMU memory management subsystem where the Xen hypervisor performs aggressive memory mapping optimizations. When guest operating systems request IOMMU mappings for device access, the hypervisor may merge multiple small mappings into larger contiguous regions to improve performance and reduce overhead. However, this optimization process fails to properly validate or isolate the mappings, allowing malicious guest code to manipulate the consolidation process and potentially overwrite or corrupt host-level memory mappings. The vulnerability specifically affects AMD x86 platforms due to differences in how the IOMMU hardware handles memory translation compared to Intel architectures, making it particularly concerning for deployments using AMD-based virtualization environments.
The operational impact of CVE-2018-19962 is severe and potentially catastrophic for virtualized environments. A malicious guest operating system user can exploit this vulnerability to escalate privileges and gain full control over the host operating system, effectively breaking the fundamental isolation guarantees that virtualization provides. This privilege escalation allows attackers to access sensitive host resources, steal data, modify system configurations, or even compromise other virtual machines running on the same physical host. The vulnerability is particularly dangerous in multi-tenant cloud environments where multiple customers share the same physical infrastructure, as it could enable attackers to move laterally between virtual machines and potentially compromise the entire hosting platform. According to CWE classification, this vulnerability maps to CWE-276: Incorrect Default Permissions, as it involves improper access control mechanisms in the memory management layer, and may also relate to CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer, given the memory manipulation aspects of the flaw.
Mitigation strategies for CVE-2018-19962 focus on both immediate patching and operational hardening measures. The primary solution involves upgrading to Xen hypervisor versions 4.12.0 and later, where the problematic IOMMU mapping consolidation logic has been completely reworked to prevent unsafe combinations of mappings. Organizations should prioritize patching their Xen deployments, particularly in production environments where guest users have elevated privileges or where sensitive data processing occurs. Additional operational mitigations include disabling IOMMU features when not required, implementing strict access controls for guest operating systems, and monitoring for unusual memory mapping patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability corresponds to T1055.011: Process Injection and T1068: Exploitation for Privilege Escalation, as it enables attackers to leverage hypervisor flaws to escalate from guest-level privileges to host-level access. Security teams should also implement network segmentation and monitoring to detect potential exploitation attempts, as the vulnerability may be used as a stepping stone for more extensive attacks within virtualized environments.