CVE-2021-28700Network attack vector

Host denial of service via unbounded guest memory

Published Aug 27, 2021 · Updated Aug 3, 2024

Resource exhaustion in Xen Hypervisor 4.12 and later allows guest OS users to crash an Arm host via dom0less memory allocation. The Arm dom0less domain-construction path leaves the domain's maximum page count unset, so its guest can allocate beyond the Device Tree memory assignment. Exploitation requires control of a dom0less guest on an Arm system and exhausts Xen's memory, interrupting every domain on the host.

CVSS severity4.9
Medium
EPSS probability1.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Xen Hypervisor 4.12 and later allows guest OS users to crash an Arm host via dom0less memory allocation. The Arm dom0less domain-construction path leaves the domain's maximum page count unset, so its guest can allocate beyond the Device Tree memory assignment. Exploitation requires control of a dom0less guest on an Arm system and exhausts Xen's memory, interrupting every domain on the host.

The record

CVE
CVE-2021-28700
Published
Aug 27, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-770, T1499.004
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Aug 27, 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 <unspecified

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Xen Project · Xen Hypervisorversion=4.12.x; version=4.13.x <unspecified

Published CVSS scores

4.9NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
6.8NIST NVDAV:N/AC:L/Au:S/C:N/I:N/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)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
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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