CVE-2021-28707

Host interruption via misaligned PoD page range

Published Nov 24, 2021 · Updated Aug 3, 2024

Denial of service in Xen Hypervisor 4.7 and later allows local users controlling a guest domain to interrupt the host via a PoD hypercall. XENMEM_populate_physmap accepts a page-order range without verifying that its base guest frame number is aligned, while downstream PoD handling assumes that alignment. Only x86 HVM or PVH guests started with maxmem greater than memory are exposed, and the caller must be a deprivileged QEMU process or stub domain that controls the guest.

CVSS severity8.8
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Xen Hypervisor 4.7 and later allows local users controlling a guest domain to interrupt the host via a PoD hypercall. XENMEM_populate_physmap accepts a page-order range without verifying that its base guest frame number is aligned, while downstream PoD handling assumes that alignment. Only x86 HVM or PVH guests started with maxmem greater than memory are exposed, and the caller must be a deprivileged QEMU process or stub domain that controls the guest.

The record

CVE
CVE-2021-28707
Published
Nov 24, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 24, 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=4.12.x <unspecified
  2. Affected versionversion=4.15.x
  3. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Xen Project · Xen Hypervisorversion=4.12.x <unspecified; version=4.15.x; version=xen-unstable

Published CVSS scores

5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
8.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
6.9NIST NVDAV:L/AC:M/Au:N/C:C/I:C/A:C

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

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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