CVE-2026-31787: xen/privcmd: fix double free via VMA splitting

Severity: high (CVSS 7.8 v3.1)
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: 2026-04-30 · updated 2026-06-17
Weakness: CWE-415

Description

In the Linux kernel, the following vulnerability has been resolved: xen/privcmd: fix double free via VMA splitting privcmd_vm_ops defines .close (privcmd_close), but neither .may_split nor .open. When userspace does a partial munmap() on a privcmd mapping, the kernel splits the VMA via __split_vma(). Since may_split is NULL, the split is allowed. vm_area_dup() copies vm_private_data (a pages array allocated in alloc_empty_pages()) into the new VMA without any fixup, because there is no .open callback. Both VMAs now point to the same pages array. When the unmapped portion is closed, privcmd_close() calls: - xen_unmap_domain_gfn_range() - xen_free_unpopulated_pages() - kvfree(pages) The surviving VMA still holds the dangling pointer. When it is later destroyed, the same sequence runs again, which leads to a double free. Fix this issue by adding a .may_split callback denying the VMA split. This is XSA-487 / CVE-2026-31787

Affected products

Linux kernel: from 3.8 before 5.10.254; from 5.11 before 5.15.204; from 5.16 before 6.1.170; from 6.2 before 6.6.137; from 6.7 before 6.12.85; from 6.13 before 6.18.26 — fixed in 5.10.254, 5.15.204, 6.1.170, 6.12.85, 6.18.26, 6.6.137

How to fix

Upgrade to a fixed version: Linux kernel 5.10.254, 5.15.204, 6.1.170, 6.12.85. Check the vendor advisory for mitigations.

References

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