CVE-2021-30178

Host crash via uninitialized Hyper-V SynIC context

Published Apr 6, 2021 · Updated Aug 3, 2024

NULL pointer dereference in Linux kernel 5.11.11 and earlier allows local users to crash the host through Hyper-V SynIC access. In arch/x86/kvm/hyperv.c, synic_get converts a KVM virtual CPU lacking initialized Hyper-V state into a SynIC context and dereferences it without first rejecting the null state. The path requires local low-privileged access and affects availability only, interrupting virtual-machine hosting when the kernel crashes.

CVSS severity5.5
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in Linux kernel 5.11.11 and earlier allows local users to crash the host through Hyper-V SynIC access. In arch/x86/kvm/hyperv.c, synic_get converts a KVM virtual CPU lacking initialized Hyper-V state into a SynIC context and dereferences it without first rejecting the null state. The path requires local low-privileged access and affects availability only, interrupting virtual-machine hosting when the kernel crashes.

The record

CVE
CVE-2021-30178
Published
Apr 6, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 6, 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?

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

2.1NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
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

CWE-476NULL Pointer Dereference
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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