CVE-2021-28701

Status: ModifiedHigh (7.8)—

Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed.

CVSS

Version: 3.1
Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Base score: 7.8

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.27%
Percentile among all scored CVEs: 17
Score date: 10/11/2026

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).

Affected technologies (3)

Debian — Debian Linux Fedoraproject — Fedora XEN — XEN

CWEs

CWE-362

References

Raw JSON (NVD)

Show

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      "value": "Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed."
    },
    {
      "lang": "es",
      "value": "Otra carrera en el manejo de la función XENMAPSPACE_grant_table de los Huéspedes, se les permite el acceso a determinadas páginas de memoria propiedad de Xen. La mayoría de estas páginas permanecen asignadas / asociadas a un huésped durante toda su vida. Las páginas de estado de la tabla Grant v2, sin embargo, se desasignan cuando un huésped cambia (de nuevo) de v2 a v1. Una liberación de dichas páginas requiere que el hipervisor haga cumplir que ninguna petición paralela pueda resultar en la adición de un mapeo de dicha página a un huésped. Esta aplicación no existía, permitiendo a los huéspedes mantener el acceso a las páginas liberadas y quizás reusarlas para otros fines. Desafortunadamente, cuando fue preparada la XSA-379, no se advirtió este problema similar"
    }
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  "lastModified": "2026-06-17T03:46:49.863",
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