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CVE-2019-18420

Status: ModifiedMedium (6.5)—

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall. hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created.

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Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability.

CVSS

Exploitation probability (EPSS)

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).

Affected technologies (3)

Debian — Debian LinuxFedoraproject — FedoraXEN — XEN

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2019-18420",
  "cveTags": [],
  "metrics": {
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          "vectorString": "AV:N/AC:M/Au:S/C:N/I:N/A:C",
          "authentication": "SINGLE",
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          "integrityImpact": "NONE",
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          "attackComplexity": "LOW",
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  "published": "2019-10-31T14:15:10.650",
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      "value": "An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall. hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created. Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability."
    },
    {
      "lang": "es",
      "value": "Se detectó un problema en Xen versiones hasta 4.12.x, permitiendo a usuarios del sistema operativo invitado PV de x86 causar una denegación de servicio por medio de una hipercall de VCPUOP_initialise. hypercall_create_continuation() es una función variadic que utiliza una cadena de formato tipo printf para interpretar sus parámetros. El manejo de errores para un carácter de formato incorrecto fue realizado utilizando BUG(), que bloquea a Xen. Una ruta, por medio de una hypercall VCPUOP_initialise, tiene un carácter de formato incorrecto. El BUG() puede ser golpeado si VCPUOP_initialise es ejecutado durante un período de tiempo suficientemente largo para que una continuación sea creada. Los invitados maliciosos pueden causar un bloqueo del hipervisor, resultando en una Denegación de Servicio (DoS). Xen versiones 4.6 y más recientes son vulnerables. Las versiones de Xen 4.5 y anteriores no son vulnerables. Solo los invitados de PV x86 pueden explotar la vulnerabilidad. Los invitados de HVM y PVH, e invitados en sistemas ARM, no pueden explotar la vulnerabilidad."
    }
  ],
  "lastModified": "2026-06-17T02:25:00.177",
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}