CVE-2021-28698

Host-wide denial of service via grant-table iteration

Published Aug 27, 2021 · Updated Aug 3, 2024

Denial of service in Xen Hypervisor 4.11.x through 4.15.x allows guest OS users to interrupt the entire host via grant mappings. Xen grant-table actions iterate across every maptrack entry, including unused and never-used entries, so an enlarged table monopolizes a CPU. A malicious or buggy guest kernel must create enough mappings; the vendor reports that default settings are generally not vulnerable, while cooperating guests can intensify the host-wide outage.

CVSS severity5.5
Medium
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 4.11.x through 4.15.x allows guest OS users to interrupt the entire host via grant mappings. Xen grant-table actions iterate across every maptrack entry, including unused and never-used entries, so an enlarged table monopolizes a CPU. A malicious or buggy guest kernel must create enough mappings; the vendor reports that default settings are generally not vulnerable, while cooperating guests can intensify the host-wide outage.

The record

CVE
CVE-2021-28698
Published
Aug 27, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-835, T1499.004
Attack vector
local
Privileges
authenticated

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=4.11.x
  2. Affected versionversion=4.12.x
  3. Affected versionversion=4.13.x
  4. Affected versionversion=4.14.x
  5. 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; version=4.13.x; version=4.14.x; version=4.15.x <unspecified

Published CVSS scores

4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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