CVEs-PoC/2021/CVE-2021-28701.md

### [CVE-2021-28701](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-28701)
![](https://img.shields.io/static/v1?label=Product&message=xen&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=4.11.x%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=4.12.x%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=4.15.x%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=unknown&color=brightgreen)

### Description

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.

### POC

#### Reference
No PoCs from references.

#### Github
- https://github.com/n0-traces/cve_monitor