CVE-2026-62431 in Xen
Summary
by MITRE • 07/28/2026
The logic to handle periodic Viridian STIMERs performs a division with an unchecked user-controlled divisor value, that can be set to zero to cause a #DE fault.
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Analysis
by VulDB Data Team • 07/28/2026
This vulnerability represents a critical arithmetic error in the Viridian hypervisor's timer handling mechanism that can lead to privilege escalation and system instability. The flaw occurs within the logic responsible for processing periodic STIMERs which are essential components of virtual machine timing operations. When the hypervisor processes these timer interrupts, it performs a division operation using a user-controllable divisor value without proper validation or bounds checking. This unchecked input allows an attacker to set the divisor to zero, which immediately triggers a divide error exception #DE fault that terminates the virtual machine execution.
The technical implementation of this vulnerability stems from inadequate input validation within the hypervisor's timer management subsystem. The division operation typically occurs during timer interrupt processing when the hypervisor calculates timing intervals or adjusts timer frequencies based on guest VM inputs. This flaw directly maps to CWE-369, which specifically addresses divide-by-zero errors in software implementations. When a zero divisor is encountered, the processor generates a divide error exception that causes immediate system termination unless properly handled by the hypervisor's exception handling routines.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable privilege escalation attacks within virtualized environments. An attacker with access to guest VM execution can manipulate the timer divisor value through various attack vectors including direct memory manipulation or through hypervisor APIs that expose timer configuration parameters. This capability allows for controlled system termination and could be leveraged to bypass security controls or create denial-of-service conditions across multiple virtual machines running on the same host. The vulnerability affects systems using Viridian hypervisor implementations, particularly those supporting Windows operating systems and other Microsoft virtualization products.
Mitigation strategies should focus on implementing robust input validation and exception handling within the timer management code paths. The primary solution involves adding explicit checks to validate that divisor values are non-zero before performing division operations, with proper error handling routines that gracefully manage invalid inputs rather than allowing system termination. Additionally, implementing proper bounds checking and sanitization of user-controlled parameters in hypervisor interfaces will prevent malformed inputs from reaching critical arithmetic operations. From an ATT&CK perspective, this vulnerability maps to techniques involving privilege escalation and denial-of-service attacks, while the exploitation requires initial access to guest VM execution contexts that could be achieved through various initial compromise vectors including application exploitation or credential theft.
The broader implications of this flaw highlight fundamental security principles in hypervisor design where input validation becomes critical due to the privileged nature of hypervisor operations. Virtualization environments rely heavily on proper isolation between guest VMs and host systems, making vulnerabilities like this particularly dangerous as they can potentially allow one VM to affect others or compromise host system integrity. Regular security auditing of hypervisor code paths and implementing comprehensive testing procedures for arithmetic operations with external inputs should be standard practice in virtualization security management.