CVE-2019-17341 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges by leveraging a page-writability race condition during addition of a passed-through PCI device.
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Analysis
by VulDB Data Team • 09/27/2020
The vulnerability identified as CVE-2019-17341 represents a critical security flaw in the Xen hypervisor affecting versions through 4.11.x. This issue specifically impacts x86 paravirtualized guest operating systems and stems from a page-writability race condition that occurs during the process of adding passed-through PCI devices. The flaw allows malicious guest users to exploit a timing window in the hypervisor's memory management operations, creating opportunities for both denial of service and privilege escalation attacks. The vulnerability resides in the hypervisor's handling of memory mappings and device passthrough mechanisms, where insufficient synchronization prevents proper validation of memory page permissions during device addition operations.
The technical implementation of this vulnerability involves a race condition between the hypervisor's page management routines and guest OS operations during PCI device assignment. When a paravirtualized guest attempts to add a passed-through PCI device, the hypervisor must update memory mappings and page permissions to ensure proper device access. However, the lack of proper synchronization between these operations creates a window where malicious guest code can manipulate page writability states, potentially leading to memory corruption or unauthorized access to hypervisor memory regions. This race condition specifically affects the hypervisor's ability to maintain consistent memory page permissions during device addition, allowing for potential privilege escalation from guest user level to hypervisor level.
The operational impact of CVE-2019-17341 extends beyond simple denial of service scenarios to include significant privilege escalation capabilities that could compromise entire virtualized environments. An attacker with access to a paravirtualized guest system could leverage this vulnerability to execute arbitrary code within the hypervisor context, potentially gaining control over all virtual machines running on the same host. This creates cascading security implications where a single compromised guest could lead to complete hypervisor compromise and subsequent attacks on all other VMs sharing the same physical hardware. The vulnerability affects systems using Xen hypervisors in cloud environments, virtualization platforms, and any deployment where paravirtualized guests are utilized with PCI device passthrough functionality.
Mitigation strategies for CVE-2019-17341 primarily involve upgrading to patched versions of the Xen hypervisor where the race condition has been addressed through improved synchronization mechanisms and proper page permission validation. Organizations should implement immediate patches to versions 4.12.0 and later, which contain the necessary fixes for this vulnerability. Additionally, security administrators should consider implementing strict access controls for PCI device passthrough operations, limiting which guest VMs can access physical devices and monitoring for anomalous memory access patterns. The mitigation approach aligns with industry standards such as CWE-362, which addresses race conditions in concurrent programming, and follows ATT&CK techniques related to privilege escalation and hypervisor attacks. Network segmentation and monitoring solutions should also be deployed to detect potential exploitation attempts and provide early warning of compromise.