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GHSA-94JH-P9FJ-QXF8

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33

Details

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

s390/mm: Fix handling of _PAGE_UNUSED pte bit

The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() that the page can be discarded instead of being moved / swapped.

KVM has no way to know why a page is being unmapped, so it sets the bit on userspace ptes corresponding to unused guest pages every time they get unmapped. KVM has no reasonable way to clear the bit once the page is in use again.

While set_ptes() checks and clears the bit, other paths that set new ptes did not. This led to used pages being thrown out as if they were unused, causing guest corruption.

Fix the issue by clearing the _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed.

Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.

Severity

9.3 (Critical)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-72412"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:22:14Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ns390/mm: Fix handling of _PAGE_UNUSED pte bit\n\nThe _PAGE_UNUSED softbit should not really be lying around. Its sole\npurpose is to signal to try_to_unmap_one() and try_to_migrate_one()\nthat the page can be discarded instead of being moved / swapped.\n\nKVM has no way to know why a page is being unmapped, so it sets the bit\non userspace ptes corresponding to unused guest pages every time they\nget unmapped. KVM has no reasonable way to clear the bit once the page\nis in use again.\n\nWhile set_ptes() checks and clears the bit, other paths that set new\nptes did not. This led to used pages being thrown out as if they were\nunused, causing guest corruption.\n\nFix the issue by clearing the _PAGE_UNUSED bit for present ptes in\nset_pte(), i.e. whenever a present pte is getting set. The check in\nset_ptes() is then redundant and can be removed.\n\nAlso fix gmap_helper_try_set_pte_unused() to only set the bit if the\npte is present; the _PAGE_UNUSED bit is only defined for present ptes\nand thus should not be set for non-present ptes.",
  "id": "GHSA-94jh-p9fj-qxf8",
  "modified": "2026-08-17T06:33:28Z",
  "published": "2026-08-15T06:32:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72412"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d4bb00704a66024502261fa7a523c07420249fea"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fda07c8e4b54b9105f1ca73f0adea7b244d405f4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-72412 (GCVE-0-2026-72412)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:56 – Updated: 2026-08-17 05:43

Title

s390/mm: Fix handling of _PAGE_UNUSED pte bit

Summary

In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() that the page can be discarded instead of being moved / swapped. KVM has no way to know why a page is being unmapped, so it sets the bit on userspace ptes corresponding to unused guest pages every time they get unmapped. KVM has no reasonable way to clear the bit once the page is in use again. While set_ptes() checks and clears the bit, other paths that set new ptes did not. This led to used pages being thrown out as if they were unused, causing guest corruption. Fix the issue by clearing the _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed. Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.

Severity

9.3 (Critical)


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

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/fda07c8e4b54b9105…
https://git.kernel.org/stable/c/d4bb00704a6602450…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: c98175b7917fa81cd499b1527c4a57fd7d36711e , < fda07c8e4b54b9105f1ca73f0adea7b244d405f4 (git) Affected: c98175b7917fa81cd499b1527c4a57fd7d36711e , < d4bb00704a66024502261fa7a523c07420249fea (git)
Linux	Linux	Affected: 7.0 Unaffected: 0 , < 7.0 (semver) Unaffected: 7.1.5 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/s390/include/asm/pgtable.h",
            "arch/s390/mm/gmap_helpers.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fda07c8e4b54b9105f1ca73f0adea7b244d405f4",
              "status": "affected",
              "version": "c98175b7917fa81cd499b1527c4a57fd7d36711e",
              "versionType": "git"
            },
            {
              "lessThan": "d4bb00704a66024502261fa7a523c07420249fea",
              "status": "affected",
              "version": "c98175b7917fa81cd499b1527c4a57fd7d36711e",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/s390/include/asm/pgtable.h",
            "arch/s390/mm/gmap_helpers.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.0"
            },
            {
              "lessThan": "7.0",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.5",
                  "versionStartIncluding": "7.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "7.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ns390/mm: Fix handling of _PAGE_UNUSED pte bit\n\nThe _PAGE_UNUSED softbit should not really be lying around. Its sole\npurpose is to signal to try_to_unmap_one() and try_to_migrate_one()\nthat the page can be discarded instead of being moved / swapped.\n\nKVM has no way to know why a page is being unmapped, so it sets the bit\non userspace ptes corresponding to unused guest pages every time they\nget unmapped. KVM has no reasonable way to clear the bit once the page\nis in use again.\n\nWhile set_ptes() checks and clears the bit, other paths that set new\nptes did not. This led to used pages being thrown out as if they were\nunused, causing guest corruption.\n\nFix the issue by clearing the _PAGE_UNUSED bit for present ptes in\nset_pte(), i.e. whenever a present pte is getting set. The check in\nset_ptes() is then redundant and can be removed.\n\nAlso fix gmap_helper_try_set_pte_unused() to only set the bit if the\npte is present; the _PAGE_UNUSED bit is only defined for present ptes\nand thus should not be set for non-present ptes."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.3,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is only reachable on s390 KVM hosts when a guest drives CMMA/ESSA page-state changes and gmap unmaps that reach gmap_helper_try_set_pte_unused() and host try_to_unmap_one()/try_to_migrate_one() on kvm-\u003emm; there is no network or physical-bus entry point.\nAC:L - A guest can deterministically mark pages unused via ESSA, remap them through PTE-install paths that left stale _PAGE_UNUSED set, then induce host reclaim/migration with memory pressure; no attacker-uncontrollable race or rare layout is required on CMMA-enabled s390 KVM.\nPR:N - A malicious KVM guest tenant on an IBM Z/LinuxONE host with CMMA-enabled VMs needs no host root, capabilities, or /dev/kvm access\u2014only guest supervisor memory management that issues ESSA and normal guest page reuse to trigger the stale-bit discard path.\nUI:N - No victim interaction is required; once a CMMA-enabled s390 KVM guest is running, the attacker directly drives ESSA unused marking, guest remap/fault activity, and memory-pressure workloads to trigger premature host-side page discard.\nS:C - The flaw corrupts host-kernel management of kvm-\u003emm backing pages from guest-controlled CMMA state, discarding live present pages outside the guest security authority and enabling cross-boundary host memory corruption/disclosure primitives.\nC:H - Prematurely discarding present backing pages while guest mappings remain can free and reallocate folios, exposing prior page contents on refault and providing UAF-class read primitives consistent with memory-corruption confidentiality impact.\nI:H - Stale _PAGE_UNUSED causes try_to_unmap_one()/try_to_migrate_one() to drop in-use guest backing pages instead of swapping/migrating them, enabling arbitrary guest memory corruption and host mm metadata corruption exploitable for control-flow hijacking.\nA:H - Incorrect discard during host reclaim, migration, or unmap can panic/oops the kernel or repeatedly corrupt guest RAM, causing guest or host denial of service that the attacker can retrigger with memory-pressure workloads."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:43:53.927Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fda07c8e4b54b9105f1ca73f0adea7b244d405f4"
        },
        {
          "url": "https://git.kernel.org/stable/c/d4bb00704a66024502261fa7a523c07420249fea"
        }
      ],
      "title": "s390/mm: Fix handling of _PAGE_UNUSED pte bit",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72412",
    "datePublished": "2026-08-15T05:56:34.165Z",
    "dateReserved": "2026-08-09T03:40:39.926Z",
    "dateUpdated": "2026-08-17T05:43:53.927Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

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GHSA-94JH-P9FJ-QXF8

CVE-2026-72412 (GCVE-0-2026-72412)

Tags

Sightings

Nomenclature