What’s Vulnerable › Vulnerabilities

CVE-2026-68166: userfaultfd: prevent registration of special VMAs

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-10 · updated 2026-08-23

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.

Affected products

• Linux kernel: 6.6 — fixed in 7.2

How to fix

Upgrade to a fixed version: Linux kernel 7.2. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/0c26202b157f1efc3cd2f26f5c30f59b508a6a5d
• https://git.kernel.org/stable/c/165613191ad9d034bf17c00e3a142f9561597ec5
• https://git.kernel.org/stable/c/3c58f641e813c3c71039f8fd4d4e2a3aab713288
• https://git.kernel.org/stable/c/495a28d5a100be1b232633f4c2dcc42ba10b3796
• https://git.kernel.org/stable/c/d974b4b786214883bd8e56bda10b454c80fd6205

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