CVE-2021-26435Network attack vector

Remote code execution via crafted scripting file

Published Sep 15, 2021 · Updated Aug 10, 2026

Memory corruption in the Windows Scripting Engine allows remote attackers to execute code through a crafted file on affected Windows releases. The engine writes beyond an allocated memory buffer while processing attacker-controlled script content, although Microsoft has not disclosed the responsible routine. Exploitation requires a user to open the file or visit crafted web content, and resulting code runs with that user's privileges.

CVSS severity8.1
High
EPSS probability5.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in the Windows Scripting Engine allows remote attackers to execute code through a crafted file on affected Windows releases. The engine writes beyond an allocated memory buffer while processing attacker-controlled script content, although Microsoft has not disclosed the responsible routine. Exploitation requires a user to open the file or visit crafted web content, and resulting code runs with that user's privileges.

The record

CVE
CVE-2021-26435
Published
Sep 15, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Windows 10 Version 1507
Classifications
CWE-787, T1204.002, T1203
Attack vector
network
Privileges
unauthenticated

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

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=10.0.10240.0 <10.0.10240.19060

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.10240.0 <10.0.10240.19060
Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7version=6.1.0 <6.1.7601.25712
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1237
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1801
Microsoft · Windows 8.1version=6.3.0 <6.3.9600.20120
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server 2012version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows Server 2008 R2 Service Pack 1 (Server Core installation)version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7 Service Pack 1version=6.1.0 <6.1.7601.25712
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 Service Pack 2version=6.0.6003.0 <6.0.6003.21218
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.230
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2183; version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows Server 2012 R2version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2008 Service Pack 2 (Server Core installation)version=6.0.6003.0 <6.0.6003.21218

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.1Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
6.8NIST NVDAV:N/AC:M/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1204.002Malicious File
T1203Exploitation for Client Execution

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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