CVE-2017-10917 in Xen
Summary
by MITRE
Xen through 4.8.x does not validate the port numbers of polled event channel ports, which allows guest OS users to cause a denial of service (NULL pointer dereference and host OS crash) or possibly obtain sensitive information, aka XSA-221.
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Analysis
by VulDB Data Team • 12/30/2020
The vulnerability identified as CVE-2017-10917 affects the Xen hypervisor version 4.8.x and earlier, representing a critical security flaw that undermines the integrity and availability of virtualized environments. This issue stems from insufficient input validation within the event channel port handling mechanism, specifically concerning the validation of port numbers for polled event channels. The flaw exists in the hypervisor's event processing logic where guest operating systems can manipulate or provide invalid port numbers, leading to unpredictable system behavior and potential exploitation by malicious actors. The vulnerability is particularly concerning because it operates at the hypervisor level, affecting all virtual machines running on the compromised system and potentially enabling attackers to compromise the entire virtualization infrastructure.
The technical implementation of this vulnerability occurs when the hypervisor processes polled event channel ports without proper validation of the port number parameters. A guest operating system can submit malformed or out-of-range port numbers to the hypervisor's event channel subsystem, causing the hypervisor to attempt to dereference NULL pointers when processing these invalid inputs. This NULL pointer dereference results in a kernel panic or system crash, effectively causing a denial of service condition that can bring down the entire host system. The vulnerability also presents potential information disclosure risks, as the improper handling of invalid port numbers may expose sensitive kernel memory contents to guest users through memory corruption or information leakage mechanisms.
The operational impact of CVE-2017-10917 extends beyond simple service disruption to encompass broader security implications within virtualized environments. Attackers can exploit this vulnerability to perform denial of service attacks against virtualized systems, potentially causing widespread disruption in cloud computing environments where multiple tenants share the same physical infrastructure. The ability to crash the host system means that attackers could potentially compromise the isolation between virtual machines, leading to cross-tenant attacks or privilege escalation opportunities. Additionally, the information disclosure aspect could enable attackers to gather sensitive kernel memory information that might be used to facilitate further exploitation attempts or to bypass security mechanisms. This vulnerability directly relates to CWE-125, which describes out-of-bounds read conditions, and CWE-476, which covers null pointer dereference issues, making it a significant concern for system administrators managing virtualized infrastructures.
Mitigation strategies for CVE-2017-10917 primarily involve applying the official security patches released by Xen Project and updating to versions 4.9.0 and later where the vulnerability has been addressed through proper input validation mechanisms. System administrators should implement immediate patch management procedures to ensure all Xen hypervisor installations are updated with the latest security fixes. Network segmentation and monitoring solutions should be deployed to detect anomalous event channel port usage patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, while also relating to T1068 for local privilege escalation and T1498 for network denial of service. Organizations should also consider implementing hypervisor-level monitoring to detect and alert on unusual event channel processing behavior, as well as maintaining comprehensive backup and recovery procedures to quickly restore services in case of successful exploitation. Additionally, guest operating system isolation measures and privilege restrictions should be enforced to limit the potential impact of compromised virtual machines.