CVE-2026-31787 is a high-severity vulnerability in the Linux kernel's xen/privcmd component involving a double free caused by VMA splitting. The flaw arises because the privcmd_vm_ops structure lacks a .may_split callback, allowing the kernel to split VMAs during partial munmap() calls without proper handling of shared page arrays. This leads to two VMAs referencing the same pages array, which is freed twice, causing memory corruption. The issue is fixed by adding a .may_split callback to deny VMA splitting.