CVE-2021-26434

SYSTEM code execution via world-writable installer directory

Published Sep 15, 2021 · Updated Aug 10, 2026

Privilege escalation in Microsoft Visual Studio 2017 and 2019 allows local users to execute arbitrary code as SYSTEM during installation. The Visual Studio installer creates a directory writable by all users after the Game development with C++ and Unreal Engine Installer workload is selected. Exploitation requires prior low-privileged code execution and the affected optional workload; successful abuse runs attacker-controlled code as SYSTEM.

CVSS severity7.8
High
EPSS probability0.88%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in Microsoft Visual Studio 2017 and 2019 allows local users to execute arbitrary code as SYSTEM during installation. The Visual Studio installer creates a directory writable by all users after the Game development with C++ and Unreal Engine Installer workload is selected. Exploitation requires prior low-privileged code execution and the affected optional workload; successful abuse runs attacker-controlled code as SYSTEM.

The record

CVE
CVE-2021-26434
Published
Sep 15, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft Visual Studio 2019
Classifications
CWE-732, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 15, 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

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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=15.0.0 <16.9.11
  2. Affected versionversion=16.0.0 <16.7.19
  3. Affected versionversion=16.0 <16.4.26
  4. Affected versionversion=16.11.0 <16.11.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft Visual Studio 2019version=15.0.0 <16.9.11; version=16.0.0 <16.7.19; version=16.0 <16.4.26; version=16.11.0 <16.11.3
Microsoft · Microsoft Visual Studio 2017version=15.9.0 <15.9.39

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C

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 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-732Incorrect Permission Assignment for Critical Resource
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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