CVE-2026-64561 (GCVE-0-2026-64561)

Vulnerability from cvelistv5 – Published: 2026-08-04 06:23 – Updated: 2026-08-08 15:13
VLAI
Title
KVM: x86: Check for invalid/obsolete root *after* making MMU pages available
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Check for invalid/obsolete root *after* making MMU pages available Check for a "stale" page fault, i.e. for an invalid and/or obsolete root, after making MMU pages available for the shadow MMU. If reclaiming shadow pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to map memory into an invalid root. On its own, populating an invalid root is "fine", but because child shadow pages inherit their parent's role, any children created during the map/fetch will be created as invalid pages, thus violating KVM's invariant that invalid pages are never on the list of active MMU pages. Note, the underlying flaw has existed since KVM first started tracking invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root pagetables"), but the true badness only came along in 2020 (Linux 5.9) with the invariant that invalid shadow pages can't be on the list of active pages. Note #2, inheriting role.invalid when creating child shadow pages is also far from ideal; that flaw will be addressed separately.
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: f95eec9bed76d42194c23153cb1cc8f186bf91cb , < 35e77467610c4a37cb0ff54ee56b85f73b1f5700 (git)
Affected: f95eec9bed76d42194c23153cb1cc8f186bf91cb , < 0026dbb7de8ea76e97d6edf42fc3cc084564e2bf (git)
Affected: f95eec9bed76d42194c23153cb1cc8f186bf91cb , < f3477a6a4164f15287444eda685b5f6405dbd1e5 (git)
Affected: f95eec9bed76d42194c23153cb1cc8f186bf91cb , < bce0d3c26e2c761a4bf43c8949f333fc7374eb2d (git)
Affected: f95eec9bed76d42194c23153cb1cc8f186bf91cb , < 2abd5287f08319fa35764566b15c6e22cb1068db (git)
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Linux Linux Affected: 5.9
Unaffected: 0 , < 5.9 (semver)
Unaffected: 6.6.148 , ≤ 6.6.* (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2-rc5 , ≤ * (original_commit_for_fix)
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{
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          "programFiles": [
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              "version": "7.2-rc5",
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Check for invalid/obsolete root *after* making MMU pages available\n\nCheck for a \"stale\" page fault, i.e. for an invalid and/or obsolete root,\nafter making MMU pages available for the shadow MMU.  If reclaiming shadow\npages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to\nmap memory into an invalid root.  On its own, populating an invalid root is\n\"fine\", but because child shadow pages inherit their parent\u0027s role, any\nchildren created during the map/fetch will be created as invalid pages,\nthus violating KVM\u0027s invariant that invalid pages are never on the list of\nactive MMU pages.\n\nNote, the underlying flaw has existed since KVM first started tracking\ninvalid roots in 2008 (commit 2e53d63acba7, \"KVM: MMU: ignore zapped root\npagetables\"), but the true badness only came along in 2020 (Linux 5.9)\nwith the invariant that invalid shadow pages can\u0027t be on the list of\nactive pages.\n\nNote #2, inheriting role.invalid when creating child shadow pages is also\nfar from ideal; that flaw will be addressed separately."
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              "value": "AV:L - The vulnerable shadow-MMU page-fault path is reached via local KVM_RUN handling of guest EPT/shadow faults (and nested EPT via paging_tmpl), not by network or adjacent-radio packets.\nAC:L - An attacker who can run nested or shadow-MMU guests controls MMU pressure (heavy nested mappings and/or KVM_SET_NR_MMU_PAGES) and concurrent faults so reclaim zaps an in-use root during make_mmu_pages_available; no attacker-uncontrollable condition is required.\nPR:L - Exploitation needs /dev/kvm access or a nested-capable guest on the host, privileges commonly available to kvm-group users or cloud tenants, not real init-namespace root or CAP_SYS_ADMIN on the create/run path.\nUI:N - Once the attacker can run the guest, they trigger reclaim and page faults entirely through their own vCPU activity with no action by another user.\nS:C - Guest-controlled faults corrupt host KVM MMU state (invalid shadow pages on active_mmu_pages and subsequent list handling), crossing the guest-to-host virtualization boundary into the host kernel authority.\nC:H - Invalid children on active_mmu_pages break zap accounting assumptions so later prepare_zap list_add on still-linked entries corrupts kernel lists, a memory-corruption primitive that can be leveraged for arbitrary host reads.\nI:H - The same active-list invariant break and linked-list corruption in host MMU teardown/reclaim paths yield writable host corruption suitable for control-flow or structure hijacking, not merely a benign accounting glitch.\nA:H - WARN_ON_ONCE skips, infinite zap loops, list corruption, and host oops/hangs are reachable when invalid shadow pages remain on active_mmu_pages, causing host and co-located VM denial of service."
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    "cveId": "CVE-2026-64561",
    "datePublished": "2026-08-04T06:23:21.094Z",
    "dateReserved": "2026-07-19T15:36:31.796Z",
    "dateUpdated": "2026-08-08T15:13:02.875Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-08-08T15:30:59+00:00",
      "cve": "CVE-2026-64561",
      "id": "CVE-2026-64561",
      "initial_release_date": "2026-08-04T00:00:00+00:00",
      "product_status:fixed": "1679",
      "product_status:known_affected": "22",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: KVM: x86: Check for invalid/obsolete root *after* making MMU pages available",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64561.json",
      "version": "3"
    }
  }
}



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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.

Sightings

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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.
  • 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.