CVE-2021-33751Public exploit

SYSTEM code execution via spaceport.sys out-of-bounds write

Published Jul 14, 2021 · Updated Aug 10, 2026

An out-of-bounds write in Windows Storage Spaces Controller allows local users to execute arbitrary code with SYSTEM privileges. Within spaceport.sys, SpIoctlSetControlWork passes a user-controlled length and buffer to memcpy without validating the destination allocation boundary. Exploitation requires low-privileged local code execution and winning an asynchronous IOCTL race; success enables a SYSTEM process, while a failed trigger can crash the host.

CVSS severity7.0
High
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An out-of-bounds write in Windows Storage Spaces Controller allows local users to execute arbitrary code with SYSTEM privileges. Within spaceport.sys, SpIoctlSetControlWork passes a user-controlled length and buffer to memcpy without validating the destination allocation boundary. Exploitation requires low-privileged local code execution and winning an asynchronous IOCTL race; success enables a SYSTEM process, while a failed trigger can crash the host.

The record

CVE
CVE-2021-33751
Published
Jul 14, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
CWE-269, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.17763.0 <10.0.17763.2061

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2061
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1110
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1679
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4530
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1110
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4530
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1110
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2061
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1110
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4530
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1110
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2061; version=10.0.17763.0 <10.0.17763.2061

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.0Microsoft CorporationCVSS:3.1/AV:L/AC:H/PR:L/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 exploitPublished

Weakness, pattern, technique

CWE-269Improper Privilege Management
T1068Exploitation for Privilege Escalation

Public exploit references

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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