CVE-2021-43056

Host crash via uncleared KVM SRR1 value

Published Oct 28, 2021 · Updated Aug 4, 2024

Denial of service in Linux kernel powerpc KVM before 5.14.15 allows guest OS users to crash a Power8 host through crafted guest activity. idle_kvm_start_guest() fails to clear the saved SRR1 wakeup value after entering a guest, causing power7_offline() to interpret stale state as a host wakeup action. Only Power8 systems using Linux as the KVM hypervisor are exposed; PowerVM systems are unaffected, and successful triggering crashes the host.

CVSS severity5.5
Medium
EPSS probability0.37%
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 Linux kernel powerpc KVM before 5.14.15 allows guest OS users to crash a Power8 host through crafted guest activity. idle_kvm_start_guest() fails to clear the saved SRR1 wakeup value after entering a guest, causing power7_offline() to interpret stale state as a host wakeup action. Only Power8 systems using Linux as the KVM hypervisor are exposed; PowerVM systems are unaffected, and successful triggering crashes the host.

The record

CVE
CVE-2021-43056
Published
Oct 28, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

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.

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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

T1499.004Application or System Exploitation

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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