CVE-2026-89775

Status: ReceivedCritical (9.3)—

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

KVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation

Computing the effects of a TLB invalidation involves looking at the size of the mapping cached by the TLB. For S1 mappings such as VNCR, this is deducted from the combination of the base granule size and the mapping level.

However, this implies that the S1 MMU is *on*. When the MMU is off, we indicate this with the level being set to a "creative" value of -127 (S1_MMU_DISABLED).

This ends-up being misinterpreted by pgshift_level_to_ttl() as it doesn't handle negative levels at all (the level is immediately cast to a u8 and only the bottom two bits considered), leading to an invalidation size of 0. Not helpful.

Read full descriptionShow less

Tidy-up pgshift_level_to_ttl() to handle these negative levels, and ttl_to_size() to always return SZ_1G when no valid TTL is present. This allows the removal of open-coded checks for similar situations.

Note that the check for a negative value not explicitely checking for S1_MMU_DISABLED is deliberate, so that actual negative levels introduced with LVA2 and D128 can take the same path if we ever support them.

CVSS

Version: 3.1
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Base score: 9.3

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.23%
Percentile among all scored CVEs: 13
Score date: 10/5/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

ExploitationT1068 Exploitation for Privilege Escalationprivilege escalation75 %
Primary impactT1059 Command and Scripting Interpreterexecution65 %
Secondary impactT1499.004 Application or System Exploitationimpact55 %

Vulnerabilidad local en kernel Linux (AV:L, PR:N, UI:N) que afecta gestión de TLB en KVM arm64. Impacto crítico (C:H/I:H/A:H) permite escalada de privilegios; ejecución de código y DoS por corrupción de memoria.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Execution Prevention Threat Intelligence Program Restrict Web-Based Content Privileged Account Management Limit Software Installation Filter Network Traffic

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Linux — Linux Kernel^AI

References

Raw JSON (NVD)

Show

{
  "id": "CVE-2026-89775",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "CHANGED",
          "version": "3.1",
          "baseScore": 9.3,
          "attackVector": "LOCAL",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 6,
        "exploitabilityScore": 2.5
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7270cc9157f474dfc46750a34c9d7defc686b2eb",
              "lessThan": "be54a70067c7dbe1381157e8a238fa4b16ea9c05",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "7270cc9157f474dfc46750a34c9d7defc686b2eb",
              "lessThan": "1c9fca34b9625a67a7f1a03c8604f3df760c6c49",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "7270cc9157f474dfc46750a34c9d7defc686b2eb",
              "lessThan": "8053393680d4fa3eb962667d2be95dd39f0940e5",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "arch/arm64/kvm/nested.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.16"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.16",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver",
              "lessThanOrEqual": "7.2.*"
            },
            {
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "arch/arm64/kvm/nested.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-16T09:17:07.850",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/1c9fca34b9625a67a7f1a03c8604f3df760c6c49",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/8053393680d4fa3eb962667d2be95dd39f0940e5",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/be54a70067c7dbe1381157e8a238fa4b16ea9c05",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "http://www.openwall.com/lists/oss-security/2026/09/16/14",
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation\n\nComputing the effects of a TLB invalidation involves looking at\nthe size of the mapping cached by the TLB. For S1 mappings such as\nVNCR, this is deducted from the combination of the base granule size\nand the mapping level.\n\nHowever, this implies that the S1 MMU is *on*. When the MMU is off,\nwe indicate this with the level being set to a \"creative\" value of\n-127 (S1_MMU_DISABLED).\n\nThis ends-up being misinterpreted by pgshift_level_to_ttl() as it\ndoesn't handle negative levels at all (the level is immediately cast\nto a u8 and only the bottom two bits considered), leading to an\ninvalidation size of 0. Not helpful.\n\nTidy-up pgshift_level_to_ttl() to handle these negative levels, and\nttl_to_size() to always return SZ_1G when no valid TTL is present.\nThis allows the removal of open-coded checks for similar situations.\n\nNote that the check for a negative value not explicitely checking for\nS1_MMU_DISABLED is deliberate, so that actual negative levels introduced\nwith LVA2 and D128 can take the same path if we ever support them."
    }
  ],
  "lastModified": "2026-09-16T18:17:19.027",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}