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CVE-2021-47450 (GCVE-0-2021-47450)

Vulnerability from cvelistv5 – Published: 2024-05-22 06:19 – Updated: 2026-08-05 08:47
VLAI
Title
KVM: arm64: Fix host stage-2 PGD refcount
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Fix host stage-2 PGD refcount The KVM page-table library refcounts the pages of concatenated stage-2 PGDs individually. However, when running KVM in protected mode, the host's stage-2 PGD is currently managed by EL2 as a single high-order compound page, which can cause the refcount of the tail pages to reach 0 when they shouldn't, hence corrupting the page-table. Fix this by introducing a new hyp_split_page() helper in the EL2 page allocator (matching the kernel's split_page() function), and make use of it from host_s2_zalloc_pages_exact().
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-22 18:46 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1025c8c0c6accfcbdc8f52ca1940160f65cd87d6 , < b372264c66ef78f2cab44e877fbd765ad6d24c39 (git)
Affected: 1025c8c0c6accfcbdc8f52ca1940160f65cd87d6 , < 1d58a17ef54599506d44c45ac95be27273a4d2b1 (git)
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Linux Linux Affected: 5.13
Unaffected: 0 , < 5.13 (semver)
Unaffected: 5.14.15 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://git.kernel.org/stable/c/b372264c66ef78f2cab44e877fbd765ad6d24c39\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/1d58a17ef54599506d44c45ac95be27273a4d2b1\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:39:59.495Z\"}}, {\"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-47450\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-05-22T18:46:22.813390Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-05-22T18:46:50.839Z\"}, \"title\": \"CISA ADP Vulnrichment\"}], \"cna\": {\"title\": \"KVM: arm64: Fix host stage-2 PGD refcount\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 8.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"AV:L - The bug is in pKVM EL2 host stage-2 PGD refcounting and is reached via local host activity (host stage-2 faults, KVM/hyp share/donate paths), not via remote packet processing.\\nAC:L - Once pKVM protected mode is enabled, emptying the last counted PTE in a concatenated PGD tail page deterministically drives that page\u0027s refcount to zero and frees it while it remains part of the live PGD; an attacker who can cause host stage-2 map/unmap churn can reliably provoke this.\\nPR:L - On the primary pKVM deployment (e.g. Android), a normal local user who can drive host MMIO/KVM-related stage-2 updates can reach the vulnerable get/put_page path without needing real root in the init namespace.\\nUI:N - No separate victim action is required; the attacker triggers the map/unmap sequence themselves.\\nS:C - Corruption is of the EL2 host stage-2 page tables that enforce the pKVM isolation boundary between the host and the hypervisor/protected VMs, so impact crosses that security authority.\\nC:H - Incorrectly freeing an in-use PGD page is a page-table UAF; reuse of that page can yield attacker-controlled stage-2 entries and arbitrary host/hyp memory disclosure across the pKVM boundary.\\nI:H - The same PGD UAF enables installation of malicious stage-2 mappings and control-flow/memory integrity breaks in the hypervisor-managed host view of physical memory.\\nA:H - Freeing or corrupting live host stage-2 PGD pages can panic EL2, oops the host, or otherwise crash the system.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"1025c8c0c6accfcbdc8f52ca1940160f65cd87d6\", \"lessThan\": \"b372264c66ef78f2cab44e877fbd765ad6d24c39\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"1025c8c0c6accfcbdc8f52ca1940160f65cd87d6\", \"lessThan\": \"1d58a17ef54599506d44c45ac95be27273a4d2b1\", \"versionType\": \"git\"}], \"programFiles\": [\"arch/arm64/kvm/hyp/include/nvhe/gfp.h\", \"arch/arm64/kvm/hyp/nvhe/mem_protect.c\", \"arch/arm64/kvm/hyp/nvhe/page_alloc.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.13\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.13\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.14.15\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.14.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"arch/arm64/kvm/hyp/include/nvhe/gfp.h\", \"arch/arm64/kvm/hyp/nvhe/mem_protect.c\", \"arch/arm64/kvm/hyp/nvhe/page_alloc.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/b372264c66ef78f2cab44e877fbd765ad6d24c39\"}, {\"url\": \"https://git.kernel.org/stable/c/1d58a17ef54599506d44c45ac95be27273a4d2b1\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: arm64: Fix host stage-2 PGD refcount\\n\\nThe KVM page-table library refcounts the pages of concatenated stage-2\\nPGDs individually. However, when running KVM in protected mode, the\\nhost\u0027s stage-2 PGD is currently managed by EL2 as a single high-order\\ncompound page, which can cause the refcount of the tail pages to reach 0\\nwhen they shouldn\u0027t, hence corrupting the page-table.\\n\\nFix this by introducing a new hyp_split_page() helper in the EL2 page\\nallocator (matching the kernel\u0027s split_page() function), and make use of\\nit from host_s2_zalloc_pages_exact().\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.14.15\", \"versionStartIncluding\": \"5.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15\", \"versionStartIncluding\": \"5.13\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T08:47:53.018Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-47450\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T08:47:53.018Z\", \"dateReserved\": \"2024-05-21T14:58:30.832Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-05-22T06:19:41.443Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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

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.