---
id: CVE-2026-31786
title: Buffer overflow in drivers/xen/sys-hypervisor.c
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  Buffer overflow in drivers/xen/sys-hypervisor.c

  The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is
  neither NUL terminated nor a string.

  The first cau…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    e3af585e1728c917682b6a3de9a69b41fb9194d4
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    8288d031a01dbacfde3fc643f7be3d23504de64d
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    f458ba102da97fafca106327086fc95f3fc764cb
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    4b4defd2fce3f966c25adabf46644a85558f1169
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    d5f59216650c51e5e3fcb7517c825bc8047f60ef
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    52cecff98bda2c51eed1c6ce9d21c5d6268fb19d
  - >-
    Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa <
    27fdbab4221b375de54bf91919798d88520c6e28
  - Linux 4.13
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:13:16.479800Z'
published: '2026-04-30'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:20:27.177Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31786'
references:
  - url: 'https://git.kernel.org/stable/c/e3af585e1728c917682b6a3de9a69b41fb9194d4'
  - url: 'https://git.kernel.org/stable/c/8288d031a01dbacfde3fc643f7be3d23504de64d'
  - url: 'https://git.kernel.org/stable/c/f458ba102da97fafca106327086fc95f3fc764cb'
  - url: 'https://git.kernel.org/stable/c/4b4defd2fce3f966c25adabf46644a85558f1169'
  - url: 'https://git.kernel.org/stable/c/5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a'
  - url: 'https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef'
  - url: 'https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d'
  - url: 'https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28'
tags:
  - cve.org
epss: 0.00209
epssPercentile: 0.10392
ingestedAt: '2026-10-16T17:24:46.675Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

Buffer overflow in drivers/xen/sys-hypervisor.c

The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is
neither NUL terminated nor a string.

The first causes a buffer overflow as sprintf in buildid_show will
read and copy till it finds a NUL.

00000000  f4 91 51 f4 dd 38 9e 9d  65 47 52 eb 10 71 db 50  |..Q..8..eGR..q.P|
00000010  b9 a8 01 42 6f 2e 32                              |...Bo.2|
00000017

So use a memcpy instead of sprintf to have the correct value:

00000000  f4 91 51 f4 dd 00 9e 9d  65 47 52 eb 10 71 db 50  |..Q.....eGR..q.P|
00000010  b9 a8 01 42                                       |...B|
00000014

(the above have a hack to embed a zero inside and check it's
returned correctly).

This is XSA-485 / CVE-2026-31786

## Affected

- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < e3af585e1728c917682b6a3de9a69b41fb9194d4`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < 8288d031a01dbacfde3fc643f7be3d23504de64d`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < f458ba102da97fafca106327086fc95f3fc764cb`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < 4b4defd2fce3f966c25adabf46644a85558f1169`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < 5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < d5f59216650c51e5e3fcb7517c825bc8047f60ef`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < 52cecff98bda2c51eed1c6ce9d21c5d6268fb19d`
- `Linux >= 84b7625728ea311ea35bdaa0eded53c1c56baeaa < 27fdbab4221b375de54bf91919798d88520c6e28`
- `Linux 4.13`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.