CVE-2026-31787

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

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.00%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-415 CWE-415

Affected Products

Vendor	Product	Versions
linux	linux_kernel	3.8 — 5.10.254
linux	linux_kernel	5.11 — 5.15.204
linux	linux_kernel	5.16 — 6.1.170
linux	linux_kernel	6.2 — 6.6.137
linux	linux_kernel	6.7 — 6.12.85
linux	linux_kernel	6.13 — 6.18.26
linux	linux_kernel	6.19 — 7.0.3
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5 https://git.kernel.org/stable/c/24daca4fc07f3ff8cd0e3f629cd982187f48436a https://git.kernel.org/stable/c/2894a351fe2ea8684919d36df3188b9a35e3926f https://git.kernel.org/stable/c/2b985d3a024b9e8c24e21671b34e855569763808 https://git.kernel.org/stable/c/402d84ad9e89bd4cbfd07ca8598532b7021daf95 https://git.kernel.org/stable/c/446ee446d9ae66f36e95c3c90bbcc4e56b94cde0 https://git.kernel.org/stable/c/71bf829800758a6e3889096e4754ef47ba7fc850 https://git.kernel.org/stable/c/dbf862ce9f009128ab86b234d91413a3e450beb4

Other References

http://www.openwall.com/lists/oss-security/2026/04/28/14 http://xenbits.xen.org/xsa/advisory-487.html

Frequently Asked Questions

What is CVE-2026-31787? +

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 It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-31787? +

CVE-2026-31787 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-31787? +

CVE-2026-31787 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-31787? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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