CVE-2026-89920 (GCVE-0-2026-89920)

Vulnerability from cvelistv5 – Published: 2026-09-16 10:32 – Updated: 2026-09-16 14:40
VLAI
Title
KVM: s390: Fix memory corruption by not reinjecting CK machine checks
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Fix memory corruption by not reinjecting CK machine checks Channel-subsystem damage machine checks are for the host channel subsystem. The guest channel subsystem is emulated in the userspace VMM. There is no point in forwarding such machine checks into the guest. This also simplifies the machine check reinjection and avoids kfree of a stack variable as reported by sashiko. There might be still machine checks that have the ck bit set with another bit (like instruction damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and ED bits already are.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 4d62fcc0b692e3b4058d7d138114c27cd8b011f7 , < 6ee52d3af2a1bf70349cf3f860933c8d221e229a (git)
Affected: 4d62fcc0b692e3b4058d7d138114c27cd8b011f7 , < 7077ec953996acc04b49d1dfc43df1c1a2a74395 (git)
Affected: 4d62fcc0b692e3b4058d7d138114c27cd8b011f7 , < 546dde823a36d7283dcf46127c2f3d093443860f (git)
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Linux Linux Affected: 4.13
Unaffected: 0 , < 4.13 (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.2.5 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/s390/include/asm/nmi.h",
            "arch/s390/kernel/nmi.c",
            "arch/s390/kvm/interrupt.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "6ee52d3af2a1bf70349cf3f860933c8d221e229a",
              "status": "affected",
              "version": "4d62fcc0b692e3b4058d7d138114c27cd8b011f7",
              "versionType": "git"
            },
            {
              "lessThan": "7077ec953996acc04b49d1dfc43df1c1a2a74395",
              "status": "affected",
              "version": "4d62fcc0b692e3b4058d7d138114c27cd8b011f7",
              "versionType": "git"
            },
            {
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              "status": "affected",
              "version": "4d62fcc0b692e3b4058d7d138114c27cd8b011f7",
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            }
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        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/s390/include/asm/nmi.h",
            "arch/s390/kernel/nmi.c",
            "arch/s390/kvm/interrupt.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.13"
            },
            {
              "lessThan": "4.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.51",
                  "versionStartIncluding": "4.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.5",
                  "versionStartIncluding": "4.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "4.13",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: s390: Fix memory corruption by not reinjecting CK machine checks\n\nChannel-subsystem damage machine checks are for the host channel\nsubsystem. The guest channel subsystem is emulated in the userspace VMM.\nThere is no point in forwarding such machine checks into the guest.\n\nThis also simplifies the machine check reinjection and avoids kfree of a\nstack variable as reported by sashiko.  There might be still machine\nchecks that have the ck bit set with another bit (like instruction\ndamage), mask out the CK bit in s390_backup_mcck_info(), like the CP and\nED bits already are."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Reached only after a local KVM_RUN puts an s390 vCPU in SIE (kvm_arch_vcpu_ioctl_run -\u003e __vcpu_run -\u003e kvm_s390_enter_exit_sie/sie64a, also vsie). A host CK machine check then hits vcpu_post_run -\u003e kvm_s390_reinject_machine_check. No network or physical path.\nAC:H - The CK bit comes from host lowcore via s390_backup_mcck_info(), not guest or ioctl input. Channel-subsystem damage is a host CSS hardware/firmware condition the attacker cannot induce; guest CSS is emulated in userspace and does not drive the host CSS.\nPR:L - KVM_CREATE_VM and KVM_RUN have no capable() check for ordinary (non-ucontrol) VMs. A kvm-group user who can open /dev/kvm, or a tenant already running in an s390 KVM guest, suffices; host init-namespace root is not required.\nUI:N - The attacker issues KVM_RUN on a vCPU they created, or a tenant guest is already in SIE. No separate victim action such as mounting a filesystem, opening a file, or attaching a device is required.\nS:C - kvm_s390_reinject_machine_check runs in the host kernel on the SIE-exit path and kfree()s a stack object, corrupting host allocator state. That crosses the KVM guest-to-hypervisor boundary and can compromise the host and co-located VMs.\nC:H - kfree() of the on-stack kvm_s390_interrupt_info treats a kernel stack address as a slab or large-kmalloc object (page_slab/free_large_kmalloc/slab_free), corrupting allocator metadata. That host-kernel memory corruption can be leveraged for disclosure.\nI:H - The same invalid free corrupts SLUB or page-allocator metadata, which can be turned into an arbitrary host write or control-flow hijack. CNA guidance scores this class of kernel memory corruption as High integrity.\nA:H - kfree of a non-slab stack address hits WARN_ON_ONCE in free_large_kmalloc or slab_free on a bogus object and oopses or panics the host kernel, denying service to the hypervisor and every co-located VM."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-16T14:40:14.105Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/6ee52d3af2a1bf70349cf3f860933c8d221e229a"
        },
        {
          "url": "https://git.kernel.org/stable/c/7077ec953996acc04b49d1dfc43df1c1a2a74395"
        },
        {
          "url": "https://git.kernel.org/stable/c/546dde823a36d7283dcf46127c2f3d093443860f"
        }
      ],
      "title": "KVM: s390: Fix memory corruption by not reinjecting CK machine checks",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89920",
    "datePublished": "2026-09-16T10:32:14.735Z",
    "dateReserved": "2026-09-11T19:38:34.775Z",
    "dateUpdated": "2026-09-16T14:40:14.105Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-89920",
      "date": "2026-09-25",
      "epss": "0.00173",
      "percentile": "0.05936"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-24T02:02:36.000Z",
      "cve": "CVE-2026-89920",
      "id": "msrc_CVE-2026-89920",
      "initial_release_date": "2026-09-17T01:14:29.000Z",
      "product_status:known_affected": "3",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "KVM: s390: Fix memory corruption by not reinjecting CK machine checks",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89920.json",
      "version": "4"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "arch/s390/include/asm/nmi.h",
                  "arch/s390/kernel/nmi.c",
                  "arch/s390/kvm/interrupt.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "versionType": "git"
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                    "versionType": "git"
                  }
                ]
              },
              {
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                "product": "Linux",
                "programFiles": [
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                  "arch/s390/kvm/interrupt.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "status": "affected",
                    "version": "4.13"
                  },
                  {
                    "lessThan": "4.13",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
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                    "status": "unaffected",
                    "version": "6.18.51",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "7.2.*",
                    "status": "unaffected",
                    "version": "7.2.5",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "7.3-rc1",
                    "versionType": "original_commit_for_fix"
                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: s390: Fix memory corruption by not reinjecting CK machine checks\n\nChannel-subsystem damage machine checks are for the host channel\nsubsystem. The guest channel subsystem is emulated in the userspace VMM.\nThere is no point in forwarding such machine checks into the guest.\n\nThis also simplifies the machine check reinjection and avoids kfree of a\nstack variable as reported by sashiko.  There might be still machine\nchecks that have the ck bit set with another bit (like instruction\ndamage), mask out the CK bit in s390_backup_mcck_info(), like the CP and\nED bits already are."
          }
        ],
        "id": "CVE-2026-89920",
        "lastModified": "2026-09-16T15:18:18.237",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "CHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.1,
              "impactScore": 6.0,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
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        },
        "published": "2026-09-16T11:17:01.073",
        "references": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/546dde823a36d7283dcf46127c2f3d093443860f"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/6ee52d3af2a1bf70349cf3f860933c8d221e229a"
          },
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/7077ec953996acc04b49d1dfc43df1c1a2a74395"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.