High [CVE-2026-68166] Linux kernel: Arbitrary code execution via userfaultfd shadow stack manipulation
This high-severity Red Hat Linux advisory covers CVE-2026-68166 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux for NVIDIA 26, Red Hat package: kernel.
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Summary
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. A local attacker with userfaultfd access could register on shadow stack Virtual Memory Areas (VMAs).
By discarding a page and injecting a page with chosen return addresses, an attacker could achieve arbitrary code execution. This vulnerability arises from the improper handling of special VMAs, including shadow stacks, allowing for manipulation of memory regions.
Red Hat severity: Important — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H). Weakness: CWE-94.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux for NVIDIA 26.
Affected products named by the advisory: Red Hat package: kernel.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 2 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 2 hours ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 2 hours ago·verify at source
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