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 9, 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 7.3 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H). Weakness: CWE-94.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat fixing advisory: RHSA-2026:61887, RHSA-2026:63129.
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 · high-confidence parse· fetched 30 days ago·verify at source
- kernel-0:6.12.0-211.50.1.el10_2
- kernel-0:5.14.0-687.44.1.el9_8
- RHSA-2026:61887
- RHSA-2026:63129
Official advisory · high-confidence parse· fetched 30 days ago·verify at source
Mitigation
Upgrade to a fixed release: kernel-0:6.12.0-211.50.1.el10_2, kernel-0:5.14.0-687.44.1.el9_8, RHSA-2026:61887, RHSA-2026:63129. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 30 days ago·verify at source
Discussion(0)
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