CVE-2017-15597 in Xen
Summary
by MITRE
An issue was discovered in Xen through 4.9.x. Grant copying code made an implication that any grant pin would be accompanied by a suitable page reference. Other portions of code, however, did not match up with that assumption. When such a grant copy operation is being done on a grant of a dying domain, the assumption turns out wrong. A malicious guest administrator can cause hypervisor memory corruption, most likely resulting in host crash and a Denial of Service. Privilege escalation and information leaks cannot be ruled out.
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Analysis
by VulDB Data Team • 01/20/2021
The vulnerability identified as CVE-2017-15597 represents a critical memory management flaw in the Xen hypervisor affecting versions through 4.9.x. This issue stems from a fundamental assumption within the grant copying mechanism that any grant pin operation would be accompanied by a valid page reference. The flaw manifests when the hypervisor processes grant copy operations on grants associated with domains that are in the process of terminating or "dying." The inconsistency between the grant copying code's assumptions and other code portions creates a dangerous scenario where memory corruption can occur during hypervisor operations.
The technical implementation of this vulnerability involves the hypervisor's grant table management system where guest administrators can manipulate grant references in ways that violate internal consistency checks. When a grant copy operation occurs on a grant from a dying domain, the expected page reference validation fails because the target page may have already been freed or marked for deallocation. This mismatch between expected and actual memory states creates a condition where the hypervisor's memory management subsystem can be corrupted through carefully crafted grant operations. The vulnerability operates at the hypervisor level, meaning that successful exploitation can compromise the entire host system's memory integrity.
The operational impact of CVE-2017-15597 extends beyond simple denial of service to potentially enable privilege escalation and information disclosure attacks. A malicious guest administrator can leverage this vulnerability to cause hypervisor memory corruption, leading to host system crashes and complete denial of service for all virtual machines hosted on that system. The memory corruption potential means that attackers could potentially execute arbitrary code within the hypervisor context, effectively breaking out of the guest isolation boundaries. This vulnerability directly relates to CWE-121 and CWE-125, which address buffer overflow conditions and out-of-bounds read/write operations in memory management systems.
Security mitigations for this vulnerability require immediate patching of affected Xen hypervisor versions to address the inconsistency in grant table handling logic. System administrators should implement strict access controls and monitoring for grant table operations, particularly those involving domains in termination states. The fix typically involves adding proper validation checks to ensure that grant copy operations verify the existence and validity of target pages before proceeding with memory operations. Organizations running Xen hypervisors should also consider implementing runtime protections and memory integrity checks to detect and prevent exploitation attempts. This vulnerability demonstrates the critical importance of maintaining consistency in hypervisor memory management operations and highlights the potential for guest administrators to compromise host security boundaries when memory validation is insufficient. The ATT&CK framework categorizes this as a privilege escalation technique through hypervisor compromise, as it enables attackers to leverage guest-level operations to affect host-level memory integrity and potentially gain elevated privileges within the virtualization environment.