CVE-2021-28706Network attack vector

Host denial of service via memory-limit overflow

Published Nov 24, 2021 · Updated Aug 3, 2024

Integer overflow in Xen Hypervisor 3.2 and later allows guest OS users to exhaust host memory through reservation hypercalls. A 32-bit calculation of a guest's requested memory increase wraps before comparison with the administrator-set upper bound. Exposure requires an x86 BIGMEM build, a host with more than 16 TiB of memory, and a guest allowed nearly 16 TiB; exhaustion can interrupt the entire host.

CVSS severity8.6
High
EPSS probability2.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in Xen Hypervisor 3.2 and later allows guest OS users to exhaust host memory through reservation hypercalls. A 32-bit calculation of a guest's requested memory increase wraps before comparison with the administrator-set upper bound. Exposure requires an x86 BIGMEM build, a host with more than 16 TiB of memory, and a guest allowed nearly 16 TiB; exhaustion can interrupt the entire host.

The record

CVE
CVE-2021-28706
Published
Nov 24, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-770, T1499
Attack vector
network
Privileges
unauthenticated

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 <unspecified
  4. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

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

Published CVSS scores

8.6NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.8NVDAV:N/AC:L/Au:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
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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