CVE-2026-31786 (GCVE-0-2026-31786)
Vulnerability from cvelistv5
Published
2026-04-30 10:31
Modified
2026-08-05 12:25
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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 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
References
Impacted products
Vendor Product Version
Linux Linux Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
Version: 84b7625728ea311ea35bdaa0eded53c1c56baeaa
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          "dateUpdated": "2026-04-30T10:39:32.708Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
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        "references": [
          {
            "url": "http://www.openwall.com/lists/oss-security/2026/04/28/12"
          },
          {
            "url": "http://xenbits.xen.org/xsa/advisory-485.html"
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        "title": "CVE Program Container"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nBuffer overflow in drivers/xen/sys-hypervisor.c\n\nThe build id returned by HYPERVISOR_xen_version(XENVER_build_id) is\nneither NUL terminated nor a string.\n\nThe first causes a buffer overflow as sprintf in buildid_show will\nread and copy till it finds a NUL.\n\n00000000  f4 91 51 f4 dd 38 9e 9d  65 47 52 eb 10 71 db 50  |..Q..8..eGR..q.P|\n00000010  b9 a8 01 42 6f 2e 32                              |...Bo.2|\n00000017\n\nSo use a memcpy instead of sprintf to have the correct value:\n\n00000000  f4 91 51 f4 dd 00 9e 9d  65 47 52 eb 10 71 db 50  |..Q.....eGR..q.P|\n00000010  b9 a8 01 42                                       |...B|\n00000014\n\n(the above have a hack to embed a zero inside and check it\u0027s\nreturned correctly).\n\nThis is XSA-485 / CVE-2026-31786"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerable buildid_show path is reached by a local read of /sys/hypervisor/properties/buildid inside a Linux Xen domain. It is not reachable directly from network packets or adjacent/physical interfaces.\nAC:L - Triggering the bug only requires reading a sysfs file, with no race or special timing. Any uncertainty about heap layout affects exploitation details, so the higher-severity low complexity is appropriate.\nPR:L - The sysfs attribute is read-only mode 0444, so any unprivileged local user in the Xen guest can access it. No capability, authentication, or real-root check gates the read path.\nUI:N - No victim action is required beyond the attacker performing the sysfs read. The vulnerable code runs synchronously in the attacker\u0027s read path.\nS:U - The impact is within the Linux Xen guest kernel security authority. This is not a Xen guest-to-host escape or cross-VM boundary violation.\nC:H - The bug performs an out-of-bounds read past the hypervisor build ID and can return adjacent kernel memory through a user-readable sysfs file. The Xen advisory states kernel secrets may be leaked.\nI:H - If no NUL byte is encountered before the PAGE_SIZE sysfs buffer is exceeded, sprintf can write past the sysfs buffer and corrupt kernel memory. The advisory identifies privilege escalation as possible, so high integrity impact is defensible.\nA:H - The out-of-bounds read/write can corrupt kernel memory and crash the guest kernel. The advisory explicitly lists DoS as a possible impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:25:11.040Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
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          "url": "https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef"
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          "url": "https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d"
        },
        {
          "url": "https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28"
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      ],
      "title": "Buffer overflow in drivers/xen/sys-hypervisor.c",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31786",
    "datePublished": "2026-04-30T10:31:28.293Z",
    "dateReserved": "2026-03-09T15:48:24.141Z",
    "dateUpdated": "2026-08-05T12:25:11.040Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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