CVE-2026-63939 (GCVE-0-2026-63939)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-20 13:41
VLAI
Title
KVM: SEV: Compute the correct max length of the in-GHCB scratch area
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Compute the correct max length of the in-GHCB scratch area When setting the length of the GHCB scratch area, and the area is in the GHCB shared buffer, set the effective length of the scratch area to the max possible size given the start of the guest-provided pointer, and the end of the shared buffer. The code was "fine" when first introduced, as KVM doesn't consult the length of the buffer when emulating MMIO, because the passed in @len always specifies the *max* size required. But for PSC requests, the incoming @len is just the minimum length (to process the header), and KVM needs to know the full size of the scratch area to avoid buffer overflows (spoiler alert). Opportunistically rename @len => @min_len to better reflect its role.
Severity
9.3 (Critical)
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 9b54e248d2644be71cb394eb85f31ad99e023a05 , < 6ca9400d36005ffdca25f80186bea781c7e1dc4c (git)
Affected: 9b54e248d2644be71cb394eb85f31ad99e023a05 , < 9f0a9e780f02c02d025a190f1885e1d1d73b87bd (git)
Affected: 9b54e248d2644be71cb394eb85f31ad99e023a05 , < 6644565527c4c5f507088b1c9ddf72de47790b68 (git)
Affected: 9b54e248d2644be71cb394eb85f31ad99e023a05 , < 5867d7e202e09f037cefe77f7af4413c7c0fa088 (git)
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Linux Linux Affected: 6.11
Unaffected: 0 , < 6.11 (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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{
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        {
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          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/sev.c"
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              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Compute the correct max length of the in-GHCB scratch area\n\nWhen setting the length of the GHCB scratch area, and the area is in the\nGHCB shared buffer, set the effective length of the scratch area to the max\npossible size given the start of the guest-provided pointer, and the end of\nthe shared buffer.\n\nThe code was \"fine\" when first introduced, as KVM doesn\u0027t consult the\nlength of the buffer when emulating MMIO, because the passed in @len always\nspecifies the *max* size required.  But for PSC requests, the incoming @len\nis just the minimum length (to process the header), and KVM needs to know\nthe full size of the scratch area to avoid buffer overflows (spoiler alert).\n\nOpportunistically rename @len =\u003e @min_len to better reflect its role."
        }
      ],
      "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"
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      "providerMetadata": {
        "dateUpdated": "2026-07-20T13:41:41.058Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/6ca9400d36005ffdca25f80186bea781c7e1dc4c"
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        },
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        },
        {
          "url": "https://git.kernel.org/stable/c/5867d7e202e09f037cefe77f7af4413c7c0fa088"
        }
      ],
      "title": "KVM: SEV: Compute the correct max length of the in-GHCB scratch area",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63939",
    "datePublished": "2026-07-19T14:55:35.743Z",
    "dateReserved": "2026-07-19T07:54:57.022Z",
    "dateUpdated": "2026-07-20T13:41:41.058Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-07-21",
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      "percentile": "0.09714"
    },
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  }
}



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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.