CVE-2021-31959Public exploitNetwork attack vector

Remote code execution via uninitialized property identifiers

Published Jun 8, 2021 · Updated Nov 19, 2024

Memory corruption in the Microsoft Windows scripting engine allows remote attackers to execute code through crafted web or file content. The jscript9.dll ByteCodeGenerator::EmitScopeObjectInit path allocates a PropertyID array without initialization, allowing stale entries to corrupt variable-scope handling. Exploitation requires a user to open the crafted content, and resulting code runs with that user's rights.

CVSS severity6.4
Medium
EPSS probability9.23%
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 Microsoft Windows scripting engine allows remote attackers to execute code through crafted web or file content. The jscript9.dll ByteCodeGenerator::EmitScopeObjectInit path allocates a PropertyID array without initialization, allowing stale entries to corrupt variable-scope handling. Exploitation requires a user to open the crafted content, and resulting code runs with that user's rights.

The record

CVE
CVE-2021-31959
Published
Jun 8, 2021
Updated
Nov 19, 2024
Vendor
Microsoft
Product
Windows 10 Version 1507
Classifications
T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 19, 2024Record 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=10.0.0 <10.0.10240.18967

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.0 <10.0.10240.18967
Microsoft · Windows Server 2019version=10.0.0 <10.0.17763.1999
Microsoft · Windows 7version=6.1.0 <6.1.7601.25632; version=6.1.0 <publication
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1052
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1621
Microsoft · Windows 8.1version=6.3.0 <1.0.0.0; version=6.3.0 <6.3.9600.20045
Microsoft · Windows Server 2012version=6.2.0 <1.0.0.0; version=6.2.0 <6.2.9200.23372
Microsoft · Windows Server 2016version=10.0.0 <10.0.14393.4467
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.0 <6.1.7601.25632; version=6.1.0 <publication
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1052
Microsoft · Windows 7 Service Pack 1version=6.1.0 <6.1.7601.25632; version=6.1.0 <publication
Microsoft · Windows 10 Version 1607version=10.0.0 <10.0.14393.4467
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1052
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.1999
Microsoft · Windows Server 2012 R2version=6.3.0 <1.0.0.0; version=6.3.0 <6.3.9600.20045

Published CVSS scores

6.4Microsoft CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:L
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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.

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 exploitPublished

Weakness, pattern, technique

T1203Exploitation for Client Execution

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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