CVE-2019-17340 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.11.x allowing x86 guest OS users to cause a denial of service or gain privileges because grant-table transfer requests are mishandled.
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Analysis
by VulDB Data Team • 09/27/2020
The vulnerability identified as CVE-2019-17340 represents a critical flaw in the Xen hypervisor affecting versions 4.11.x and earlier, specifically within the x86 guest operating system context. This issue stems from improper handling of grant-table transfer requests, which are fundamental mechanisms used for memory sharing between guest operating systems and the hypervisor. The grant table functionality enables efficient memory management by allowing guests to share pages with the hypervisor and other guests, making it a core component of Xen's virtualization architecture. When these transfer requests are mishandled, they create opportunities for exploitation that can lead to either denial of service conditions or privilege escalation attacks.
The technical root cause of this vulnerability lies in the insufficient validation and processing of grant table operations within the hypervisor's memory management subsystem. Grant tables serve as the interface for mapping guest physical addresses to hypervisor virtual addresses, enabling efficient data sharing and communication between virtual machines and the underlying hardware. When malicious or malformed grant table transfer requests are submitted by x86 guest operating systems, the hypervisor fails to properly validate these operations, leading to potential memory corruption or unexpected behavior. This mismanagement can result in the hypervisor crashing or entering an inconsistent state, thereby causing denial of service, or more critically, allowing guest users to execute code with elevated privileges within the hypervisor context.
The operational impact of CVE-2019-17340 extends beyond simple service disruption, as it represents a potential pathway for privilege escalation attacks that could compromise the entire virtualization environment. Attackers exploiting this vulnerability could leverage the mishandled grant table requests to execute arbitrary code with hypervisor privileges, effectively breaking the isolation guarantees that virtualization platforms are designed to provide. This scenario creates a significant security risk for cloud environments and data centers that rely on Xen hypervisors, as a compromised guest could potentially access or manipulate other virtual machines running on the same host. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and demonstrates how improper memory handling in hypervisor components can lead to severe security implications.
From a threat modeling perspective, this vulnerability operates within the ATT&CK framework's privilege escalation and defense evasion domains, as it enables attackers to gain higher privileges and potentially evade detection mechanisms. The exploitability of CVE-2019-17340 requires guest-level access, making it particularly concerning for multi-tenant cloud environments where guest isolation is paramount. Organizations running affected Xen versions should prioritize immediate patching, as the vulnerability can be exploited without requiring special privileges beyond what is normally available to guest operating systems. Mitigation strategies include updating to Xen versions 4.12.0 and later, where the grant table handling has been properly addressed, implementing additional monitoring for suspicious grant table activity, and maintaining strict access controls to prevent unauthorized guest modifications. The vulnerability underscores the critical importance of proper input validation and memory management in hypervisor components, as these systems form the foundation of modern virtualized infrastructure security.