FKIE_CVE-2026-23553

Vulnerability from fkie_nvd - Published: 2026-01-28 16:16 - Updated: 2026-02-09 18:46
Severity ?
2.9 (Low) - CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Summary
In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider: 1) vCPU runs on CPU A, running task 1. 2) vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB. 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB. 4) vCPU moves back to CPU A. Xen skips IBPB again. Now, task 2 is running on CPU A with task 1's training still in the BTB.
References
security@xen.orghttps://xenbits.xenproject.org/xsa/advisory-479.htmlMitigation, Patch, Vendor Advisory
af854a3a-2127-422b-91ae-364da2661108http://www.openwall.com/lists/oss-security/2026/01/27/3Mailing List, Mitigation, Patch, Third Party Advisory
af854a3a-2127-422b-91ae-364da2661108http://xenbits.xen.org/xsa/advisory-479.htmlMitigation, Patch, Vendor Advisory
Impacted products
Vendor Product Version
xen xen *
To clipboard 

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:o:xen:xen:*:*:*:*:*:*:x86:*",
              "matchCriteriaId": "4B8D71AF-016B-49EF-AE2B-95DEDE3BE3C3",
              "versionStartIncluding": "4.6.0",
              "vulnerable": true
            }
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          "negate": false,
          "operator": "OR"
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the context switch logic Xen attempts to skip an IBPB in the case of\na vCPU returning to a CPU on which it was the previous vCPU to run.\nWhile safe for Xen\u0027s isolation between vCPUs, this prevents the guest\nkernel correctly isolating between tasks.  Consider:\n\n 1) vCPU runs on CPU A, running task 1.\n 2) vCPU moves to CPU B, idle gets scheduled on A.  Xen skips IBPB.\n 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB.\n 4) vCPU moves back to CPU A.  Xen skips IBPB again.\n\nNow, task 2 is running on CPU A with task 1\u0027s training still in the BTB."
    },
    {
      "lang": "es",
      "value": "En la l\u00f3gica de conmutaci\u00f3n de contexto, Xen intenta omitir un IBPB en el caso de que una vCPU regrese a una CPU en la que fue la vCPU anterior en ejecutarse. Si bien es seguro para el aislamiento de Xen entre vCPUs, esto impide que el kernel invitado a\u00edsle correctamente entre tareas. Considere:\n\n1) La vCPU se ejecuta en la CPU A, ejecutando la tarea 1.\n2) La vCPU se mueve a la CPU B, el proceso inactivo se programa en A. Xen omite el IBPB.\n3) En la CPU B, el kernel invitado cambia de la tarea 1 a la 2, emitiendo un IBPB.\n4) La vCPU regresa a la CPU A. Xen omite el IBPB de nuevo.\n\nAhora, la tarea 2 se est\u00e1 ejecutando en la CPU A con el entrenamiento de la tarea 1 todav\u00eda en el BTB."
    }
  ],
  "id": "CVE-2026-23553",
  "lastModified": "2026-02-09T18:46:17.720",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "LOCAL",
          "availabilityImpact": "NONE",
          "baseScore": 2.9,
          "baseSeverity": "LOW",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 1.4,
        "impactScore": 1.4,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-01-28T16:16:16.853",
  "references": [
    {
      "source": "security@xen.org",
      "tags": [
        "Mitigation",
        "Patch",
        "Vendor Advisory"
      ],
      "url": "https://xenbits.xenproject.org/xsa/advisory-479.html"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
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      "url": "http://www.openwall.com/lists/oss-security/2026/01/27/3"
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    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
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      "url": "http://xenbits.xen.org/xsa/advisory-479.html"
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  "sourceIdentifier": "security@xen.org",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-665"
        },
        {
          "lang": "en",
          "value": "CWE-693"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}


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