CVE-2026-31590: Linux Kernel SEV Memory Vulnerability

CVE-2026-31590 Overview

A vulnerability has been identified in the Linux kernel's KVM (Kernel-based Virtual Machine) SEV (Secure Encrypted Virtualization) implementation. The issue exists in the sev_pin_memory() function where a WARN is triggered when the number of pages (npages) overflows an integer type. This vulnerability can be trivially exploited from userspace to cause a denial of service condition through the KVM_MEMORY_ENCRYPT_REG_REGION ioctl.

The flaw stems from insufficient validation in sev_mem_enc_register_region() where checks intended to verify incoming address and size values are ineffective because both parameters are already u64 types on a 64-bit only SEV architecture, making it impossible for them to exceed ULONG_MAX.

Critical Impact
Local attackers with access to KVM can trigger kernel warnings and potentially cause system instability through crafted memory encryption region requests.

Affected Products

Linux Kernel (multiple versions with KVM SEV support)
Linux-based systems with AMD SEV virtualization enabled
Virtual machine hosts utilizing KVM with SEV encryption

Discovery Timeline

April 24, 2026 - CVE-2026-31590 published to NVD
April 28, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31590

Vulnerability Analysis

This vulnerability affects the Linux kernel's handling of memory encryption region registration for AMD SEV (Secure Encrypted Virtualization) in KVM. The core issue lies in the sev_pin_memory() function which emits a WARN when the calculated number of pages overflows the capacity of an integer variable.

The vulnerability is particularly concerning because it requires only local access to trigger. An unprivileged user with access to KVM can craft a malicious kvm_enc_region structure with specially crafted address and size values to trigger the warning condition. The attack does not require any user interaction and can be executed with low attack complexity.

Root Cause

The root cause is twofold:

Inadequate overflow handling: The sev_pin_memory() function uses a WARN macro when detecting an integer overflow condition for npages, which can be triggered by userspace input.
Ineffective input validation: The boundary checks in sev_mem_enc_register_region() that compare range->addr and range->size against ULONG_MAX are completely ineffective. Since both fields are u64 types and SEV operates exclusively on 64-bit systems, these values can never exceed ULONG_MAX, rendering the validation checks useless.

Attack Vector

The attack exploits the local interface through the KVM_MEMORY_ENCRYPT_REG_REGION ioctl. An attacker can construct a kvm_enc_region structure with malicious values to trigger the integer overflow condition.

The attack methodology involves:

Creating a KVM virtual machine instance
Constructing a kvm_enc_region structure with .addr = 0 and .size = -1ul (which becomes ULONG_MAX)
Issuing the KVM_MEMORY_ENCRYPT_REG_REGION ioctl with the malicious structure
The resulting calculation causes npages to overflow, triggering the kernel WARN

This can lead to system log flooding, potential kernel instability, and denial of service conditions on systems running KVM with SEV support.

Detection Methods for CVE-2026-31590

Indicators of Compromise

Unexpected kernel warnings in system logs related to sev_pin_memory() or KVM SEV memory operations
Repeated KVM_MEMORY_ENCRYPT_REG_REGION ioctl calls with unusually large size parameters
System instability or performance degradation on KVM hosts with SEV enabled

Detection Strategies

Monitor kernel logs (dmesg, /var/log/kern.log) for WARN stack traces originating from sev_pin_memory() or related KVM SEV functions
Implement audit rules to track KVM_MEMORY_ENCRYPT_REG_REGION ioctl calls and flag requests with abnormally large size values
Deploy endpoint detection solutions capable of monitoring KVM-related system calls for anomalous patterns

Monitoring Recommendations

Enable comprehensive kernel logging and configure log aggregation to capture KVM-related warnings
Implement rate limiting on KVM ioctl operations to mitigate potential DoS attempts
Monitor system resource utilization on KVM hosts for signs of exploitation attempts

How to Mitigate CVE-2026-31590

Immediate Actions Required

Update the Linux kernel to a patched version that includes the fix for this vulnerability
Restrict access to KVM devices (/dev/kvm) to only trusted users and processes
Review and audit which users and applications have access to virtualization capabilities

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix drops the problematic WARN in sev_pin_memory() when npages overflows, and adds explanatory comments regarding the page calculation methodology. Multiple patch commits are available across different kernel branches:

Workarounds

Restrict access to /dev/kvm using file permissions or SELinux/AppArmor policies to limit potential attackers
If SEV functionality is not required, consider disabling AMD SEV support in the kernel configuration (CONFIG_AMD_MEM_ENCRYPT)
Implement system call filtering using seccomp to restrict KVM ioctl access for non-essential processes

bash

# Restrict /dev/kvm access to specific group
chmod 660 /dev/kvm
chown root:kvm /dev/kvm

# Add trusted users to kvm group only
usermod -aG kvm trusted_virt_user