CVE-2021-28687

Guest-triggered toolstack crash via uninitialized soft-reset state

Published Jun 11, 2021 · Updated Aug 3, 2024

Missing initialization in Xen Project Xen Hypervisor 4.12 through 4.14 allows guest OS users to crash a management daemon via HVM soft reboot. The soft-reset path leaves libxl__domain_suspend_state uninitialized, so later code encounters an unexpected state and triggers assert(). Security impact requires an HVM guest monitored by a consequential libxl-linked daemon such as libvirt; xl-only deployments merely leave that guest hung.

CVSS severity5.5
Medium
EPSS probability0.31%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing initialization in Xen Project Xen Hypervisor 4.12 through 4.14 allows guest OS users to crash a management daemon via HVM soft reboot. The soft-reset path leaves libxl__domain_suspend_state uninitialized, so later code encounters an unexpected state and triggers assert(). Security impact requires an HVM guest monitored by a consequential libxl-linked daemon such as libvirt; xl-only deployments merely leave that guest hung.

The record

CVE
CVE-2021-28687
Published
Jun 11, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-909, T1489
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 11, 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 <unspecified
  2. Affected versionversion=4.14.x
  3. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

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

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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-909Missing Initialization of Resource
T1489Service Stop

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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