CVE-2021-28696

Guest privilege escalation via stale IOMMU mappings

Published Aug 27, 2021 · Updated Aug 3, 2024

Incorrect authorization in Xen Hypervisor on affected AMD x86 systems allows guest OS users to access host memory after device de-assignment. The AMD IOMMU teardown path leaves firmware-defined identity mappings installed when a passed-through physical device is removed from a guest. Exploitation requires PCI passthrough on an x86 host with an IOMMU and applicable ACPI identity-mapped regions; consequences are system-dependent privilege escalation, information disclosure, or service interruption.

CVSS severity6.8
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in Xen Hypervisor on affected AMD x86 systems allows guest OS users to access host memory after device de-assignment. The AMD IOMMU teardown path leaves firmware-defined identity mappings installed when a passed-through physical device is removed from a guest. Exploitation requires PCI passthrough on an x86 host with an IOMMU and applicable ACPI identity-mapped regions; consequences are system-dependent privilege escalation, information disclosure, or service interruption.

The record

CVE
CVE-2021-28696
Published
Aug 27, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-863, T1068
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
  6. Affected versionversion=xen-unstable

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; version=xen-unstable

Published CVSS scores

6.8NIST NVDCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

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)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
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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