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

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.

Details

Source

Microsoft Security Response Center (INTL · vendor-psirt · site)

Severity

critical — CVSS 9.8

Published

2026-08-11

Exploitation

Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-68166

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

• Low exploitation riskCVE-2026-681660.20% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 10% of all EPSS-scored CVEs.

Referenced CVEs

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

• unknownDSA-6466-1 linux - security updatedebian
• unknownCVE-2026-68166: In the Linux kernel, the following vulnerability has been resolved: userfaultfd: prevent regis…nvd

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