CVE-2021-28695

Guest privilege escalation via overbroad IOMMU identity mapping

Published Aug 27, 2021 · Updated Aug 3, 2024

Incorrect IOMMU mapping in all Xen Hypervisor versions allows guest OS users to escalate privileges, interrupt service, or disclose data. On AMD x86 systems, Xen identity-maps the excluded middle of a firmware-declared discontinuous untranslated-memory range, exposing memory that should remain translated. Exploitation requires an IOMMU, applicable ACPI identity-map entries, and PCI passthrough to the guest; actual exposure depends on hardware and firmware use of those regions.

CVSS severity6.8
Medium
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect IOMMU mapping in all Xen Hypervisor versions allows guest OS users to escalate privileges, interrupt service, or disclose data. On AMD x86 systems, Xen identity-maps the excluded middle of a firmware-declared discontinuous untranslated-memory range, exposing memory that should remain translated. Exploitation requires an IOMMU, applicable ACPI identity-map entries, and PCI passthrough to the guest; actual exposure depends on hardware and firmware use of those regions.

The record

CVE
CVE-2021-28695
Published
Aug 27, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
T1068
Attack vector
Unavailable
Privileges
Unavailable

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
  6. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

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; version=xen-unstable

Published CVSS scores

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
6.8NIST NVDCVSS:3.1/AV:P/AC:L/PR:N/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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

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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