CVE-2019-17348 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 because of an incompatibility between Process Context Identifiers (PCID) and shadow-pagetable switching.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/27/2020
The vulnerability identified as CVE-2019-17348 represents a critical denial of service flaw within the Xen hypervisor ecosystem affecting versions through 4.11.x. This issue specifically impacts x86 ParaVirtualized (PV) guest operating systems and stems from an incompatibility between Process Context Identifiers and shadow pagetable switching mechanisms. The flaw manifests when PV guest users attempt to leverage certain memory management operations that trigger conflicts between the PCID functionality and the hypervisor's shadow page table implementation. This incompatibility creates a scenario where legitimate guest OS operations can cause the hypervisor to enter an inconsistent state, ultimately leading to system instability and potential complete system crashes. The vulnerability exists at the intersection of hardware virtualization features and hypervisor memory management, making it particularly challenging to detect and mitigate.
The technical root cause of this vulnerability lies in the improper handling of Process Context Identifiers within the shadow pagetable management system of the Xen hypervisor. When PV guests utilize PCID functionality, the hypervisor's shadow page table switching mechanism fails to properly account for the context identifiers, resulting in memory management inconsistencies. This incompatibility allows malicious or malformed guest OS operations to trigger page table inconsistencies that cause the hypervisor to crash or become unresponsive. The flaw operates at the hypervisor level rather than the guest OS level, making it particularly dangerous as it can affect the entire virtualization environment. The vulnerability is classified under CWE-119 as a weakness related to memory access violations and can be mapped to ATT&CK technique T1499.004 for endpoint denial of service, as it specifically targets the availability of virtualized endpoints through hypervisor instability.
The operational impact of CVE-2019-17348 extends beyond simple denial of service, as it can lead to complete system outages in virtualized environments. Organizations running Xen hypervisors in production environments face significant risk when exposed to this vulnerability, as it can be exploited by malicious actors to disrupt services or cause cascading failures across multiple virtual machines. The vulnerability affects any x86 PV guest operating systems running on affected Xen versions, making it particularly concerning for cloud providers and data centers that rely heavily on virtualization. The exploitability of this vulnerability is relatively straightforward, requiring only that a PV guest user execute specific memory management operations that trigger the PCID-shadow pagetable conflict. This makes the vulnerability particularly dangerous in multi-tenant environments where guest users may have elevated privileges or where privilege escalation occurs.
Mitigation strategies for CVE-2019-17348 primarily focus on upgrading to patched versions of the Xen hypervisor, specifically versions 4.12.0 and later where the PCID-shadow pagetable incompatibility has been resolved. Organizations should implement immediate patch management procedures to ensure all Xen installations are updated to secure versions. Additionally, administrators can consider disabling PCID functionality in affected configurations as a temporary workaround, though this may impact performance. Monitoring systems should be enhanced to detect unusual memory management patterns that might indicate exploitation attempts. The vulnerability highlights the importance of thorough testing of virtualization features, particularly when combining hardware virtualization extensions with hypervisor memory management systems. Security teams should also review their virtualization security policies and ensure proper isolation between guest operating systems to limit potential impact if exploitation occurs. This vulnerability demonstrates the critical need for comprehensive virtualization security testing and the importance of maintaining up-to-date hypervisor implementations to prevent exploitation of memory management flaws that can compromise entire virtualized infrastructures.