CVE-2026-68166

Received Received - Intake

userfaultfd Special VMA Registration Prevention in Linux Kernel

Publication date: 2026-08-10

Last updated on: 2026-08-23

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: prevent registration of special VMAs Vova Tokarev says: userfaultfd allows registration on shadow stack VMAs. With userfaultfd access, you can register on the shadow stack, discard a page ... and inject a page with chosen return addresses via UFFDIO_COPY. Update vma_can_userfault() to reject VM_SHADOW_STACK. While on it, also reject VM_SPECIAL so that if a driver would implement vm_uffd_ops, it wouldn't be possible to register special VMAs with userfaultfd. Since VM_SPECIAL includes VM_DONTEXPAND which is set but hugetlb, exclude hugetlb VMAs from the check for VM_SPECIAL.

CVSS Scores

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Meta Information

Published

2026-08-10

Last Modified

2026-08-23

Generated

2026-08-30

AI Q&A

2026-08-10

EPSS Evaluated

2026-08-29

NVD

CVE-2026-68166

EUVD

EUVD-2026-55552

Affected Vendors & Products

Vendor	Product	Version / Range
linux_kernel	userfaultfd	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves userfaultfd, a feature that allows handling page faults in user space. The issue allows registration on special VMAs like shadow stack VMAs. An attacker could exploit this to discard a page and inject a new one with chosen return addresses via UFFDIO_COPY, potentially leading to arbitrary code execution or privilege escalation.

Detection Guidance

This vulnerability is specific to the Linux kernel's userfaultfd feature and requires kernel-level inspection. Check if userfaultfd is enabled on your system by running: grep USERFAULTFD /boot/config-$(uname -r). If enabled, verify kernel version is patched by checking uname -a against the fixed version.

Impact Analysis

If exploited, this vulnerability could allow an attacker to gain elevated privileges, execute arbitrary code, or bypass security mechanisms on a system running a vulnerable Linux kernel. It primarily affects systems using userfaultfd with shadow stack or special VMAs.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards. It is a Linux kernel issue related to userfaultfd and shadow stack VMAs, which could allow unauthorized memory manipulation but does not inherently violate data protection or privacy regulations.

Mitigation Strategies

Update your Linux kernel to the latest patched version that resolves this issue. Disable userfaultfd if not needed by setting CONFIG_USERFAULTFD=n in kernel config and recompiling. Monitor vendor advisories for kernel updates.

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