CVE-2021-28709

Host denial of service via partial P2M insertion

Published Nov 24, 2021 · Updated Aug 3, 2024

Improper P2M update handling in Xen Hypervisor 4.12.x through 4.15.x and xen-unstable allows guest OS users to interrupt the host. During insertion of new pages, the PoD P2M path splits ordered hypercall ranges but fails to account for chunks completed before a later error. Only x86 HVM or PVH guests started with maxmem greater than memory can reach the flaw; a malicious guest kernel can interrupt the entire host.

CVSS severity7.8
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper P2M update handling in Xen Hypervisor 4.12.x through 4.15.x and xen-unstable allows guest OS users to interrupt the host. During insertion of new pages, the PoD P2M path splits ordered hypercall ranges but fails to account for chunks completed before a later error. Only x86 HVM or PVH guests started with maxmem greater than memory can reach the flaw; a malicious guest kernel can interrupt the entire host.

The record

CVE
CVE-2021-28709
Published
Nov 24, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-755, T1499.004
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
  2. Affected versionversion=4.13.x
  3. Affected versionversion=4.14.x
  4. Affected versionversion=4.15.x
  5. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Xen Project · Xen Hypervisorversion=4.12.x; version=4.13.x; version=4.14.x; version=4.15.x; version=xen-unstable

Published CVSS scores

6.9NIST NVDAV:L/AC:M/Au:N/C:C/I:C/A:C
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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 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

CWE-755Improper Handling of Exceptional Conditions
T1499.004Application or System Exploitation

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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