CVE-2026-68166
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.
CSIRTS triage
- What
- The userfaultfd subsystem allows registration of special virtual memory areas that should be restricted, enabling privilege escalation.
- Who is affected
- Any system running Linux kernel with userfaultfd enabled and unprivileged user namespace creation available.
- Urgency
- Critical; CVSS 9.8 and privilege escalation path warrant immediate patching.
- Action
- Apply Linux kernel security patch for userfaultfd registration restrictions immediately.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.20% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 10% of all EPSS-scored CVEs.
Advisory coverage (3)
- unknownDSA-6466-1 linux - security updatedebian · 2026-08-25
- criticalCVE-2026-68166: userfaultfd: prevent registration of special VMAsmsrc · 2026-08-11
- unknownCVE-2026-68166: In the Linux kernel, the following vulnerability has been resolved: userfaultfd: prevent regis…nvd · 2026-08-10
External references
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