# CVE-2026-31787

> Vulnerability · severity: **HIGH** (CVSS 7.8).

## 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

## Key facts

- **CVE ID:** CVE-2026-31787
- **Published:** 2026-04-30
- **CVSS severity:** HIGH
- **CVSS base score:** 7.8
- **CWE codes:** CWE-415

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31787

## Citation

> AI Analytics. CVE-2026-31787. Retrieved 2026-07-31 from https://api.ai-analytics.org/cve/CVE-2026-31787. Derived from NIST NVD. Licensed CC0.

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