CVE-2021-28701

Guest-to-host escalation via grant-table status-page race

Published Sep 8, 2021 · Updated Aug 3, 2024

Race condition in XENMAPSPACE_grant_table in Xen Hypervisor 4.0 and later allows guest OS users to gain host privileges. When a guest switches from grant table v2 to v1, the handler frees status pages without blocking a parallel mapping request, leaving freed or reused pages accessible. Exploitation requires an x86 HVM or PVH guest permitted to use grant table v2 and can also disclose information or interrupt the host or guests.

CVSS severity7.8
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in XENMAPSPACE_grant_table in Xen Hypervisor 4.0 and later allows guest OS users to gain host privileges. When a guest switches from grant table v2 to v1, the handler frees status pages without blocking a parallel mapping request, leaving freed or reused pages accessible. Exploitation requires an x86 HVM or PVH guest permitted to use grant table v2 and can also disclose information or interrupt the host or guests.

The record

CVE
CVE-2021-28701
Published
Sep 8, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-362, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.11.x
  2. Affected versionversion=4.12.x <unspecified
  3. Affected versionversion=4.15.x <unspecified

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Xen Project · Xen Hypervisorversion=4.11.x; version=4.12.x <unspecified; version=4.15.x <unspecified

Published CVSS scores

4.4NIST NVDAV:L/AC:M/Au:N/C:P/I:P/A:P
7.8NIST NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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