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GHSA-3C28-G28M-GM93

Vulnerability from github – Published: 2026-04-30 12:33 – Updated: 2026-05-06 21:31
VLAI
Details

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

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-31787"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-415"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-30T11:16:21Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nxen/privcmd: fix double free via VMA splitting\n\nprivcmd_vm_ops defines .close (privcmd_close), but neither .may_split\nnor .open. When userspace does a partial munmap() on a privcmd mapping,\nthe kernel splits the VMA via __split_vma(). Since may_split is NULL,\nthe split is allowed. vm_area_dup() copies vm_private_data (a pages\narray allocated in alloc_empty_pages()) into the new VMA without any\nfixup, because there is no .open callback.\n\nBoth VMAs now point to the same pages array. When the unmapped portion\nis closed, privcmd_close() calls:\n    - xen_unmap_domain_gfn_range()\n    - xen_free_unpopulated_pages()\n    - kvfree(pages)\n\nThe surviving VMA still holds the dangling pointer. When it is later\ndestroyed, the same sequence runs again, which leads to a double free.\n\nFix this issue by adding a .may_split callback denying the VMA split.\n\nThis is XSA-487 / CVE-2026-31787",
  "id": "GHSA-3c28-g28m-gm93",
  "modified": "2026-05-06T21:31:31Z",
  "published": "2026-04-30T12:33:12Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31787"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/24daca4fc07f3ff8cd0e3f629cd982187f48436a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2894a351fe2ea8684919d36df3188b9a35e3926f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2b985d3a024b9e8c24e21671b34e855569763808"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/402d84ad9e89bd4cbfd07ca8598532b7021daf95"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/446ee446d9ae66f36e95c3c90bbcc4e56b94cde0"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/71bf829800758a6e3889096e4754ef47ba7fc850"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/dbf862ce9f009128ab86b234d91413a3e450beb4"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/04/28/14"
    },
    {
      "type": "WEB",
      "url": "http://xenbits.xen.org/xsa/advisory-487.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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