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Full vulnerability report · 2021
CVE-2021-34448High confidence

Microsoft Windows Scripting Engine Memory Corruption Vulnerability

Microsoft · Windows

6.8MediumCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Critical, raised 2 bands.upgradedsince 3 Nov 2021

Evidence used

  • CISA confirms exploitation in the wild.
  • EPSS is 40.06% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Microsoft Windows and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-21103

CISA KEV mirrored by ENISA

Scripting Engine Memory Corruption Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 3 Nov 2021. Evidence sources: cisa_kev.
ENISA score
6.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
01

What, why and how

Microsoft Windows Scripting Engine contains an unspecified vulnerability that allows for memory corruption.

What

Microsoft Windows Scripting Engine contains an unspecified vulnerability that allows for memory corruption.

Why

A bounds error lets data be written beyond the intended memory region, potentially corrupting control data.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Microsoft Windows Scripting Engine contains an unspecified vulnerability that allows for memory corruption.

Why

A bounds error lets data be written beyond the intended memory region, potentially corrupting control data.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2021-11-03.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Out-of-bounds Write → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-787 ↗

CWE-787: Out-of-bounds Write. The product writes data past the end, or before the beginning, of the intended buffer.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-787CISA KEV
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2021-21103Known-exploited evidence recorded

Scripting Engine Memory Corruption Vulnerability

Official EUVD record ↗
Canadian Centre for Cyber Security · English · AV21-335Microsoft security advisory – July 2021 monthly rollup

On 13 July 2021 Microsoft published Security Updates to address vulnerabilities in multiple products. Included were critical updates for the following: Exploitation of some of these vulnerabilities could allow an actor to execute code remotely.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210721Security Bulletin 21 Jul 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 21 Jul 2021, published on 21 July 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-520Multiples vulnérabilités dans Microsoft Windows

d?id=CVE-2021-34438 Référence CVE CVE-2021-34439 https://www.cve.org/CVERecord?id=CVE-2021-34439 Référence CVE CVE-2021-34440 https://www.cve.org/CVERecord?id=CVE-2021-34440 Référence CVE CVE-2021-34441 https://www.cve.org/CVERecord?id=CVE-2021-34441 Référence CVE CVE-2021-34442 https://www.cve.org/CVERecord?id=CVE-2021-34442 Référence CVE CVE-2021-34444 https://www.cve.org/CVERecord?id=CVE-2021-34444 Référence CVE CVE-2021-34445 https://www.cve.org/CVERecord?id=CVE-2021-34445 Référence CVE CVE-2021-34446 https://www.cve.org/CVERecord?id=CVE-2021-34446 Référence CVE CVE-2021-34447 https://www.cve.org/CVERecord?id=CVE-2021-34447 Référence CVE CVE-2021-34448 https://www.cve.org/CVERecord?id=CVE-2021-34448 Référence CVE CVE-2021-34449 https://www.cve.org/CVERecord?id=CVE-2021-34449 Référence CVE CVE-2021-34450 https://www.cve.org/CVERecord?id=CVE-2021-34450 Référence CVE CVE-2021-34454 https://www.cve.org/CVERecord?id=CVE-2021-34454 Référence CVE CVE-2021-34455 https://www.cve.org/CVERecord?id=CVE-2021-34455 Référence CVE CVE-2021-34456 https://www.cve.org/CVERecord?id=CVE-2021-34456 Référence CVE CVE-2021-34457 https://www.cve.org/CVERecord?id=CVE-2021-34457 Référence CVE CVE-2021-34458 https://www.cve.org/CVERecord?id=CVE-2021-34458 Référence CVE CVE-2021-34459 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002217複数の Microsoft Windows 製品におけるメモリ破損の脆弱性

複数の Microsoft Windows 製品には、スクリプト エンジンに不備があるため、メモリ破損の脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5338MS 7월 보안 위협에 따른 정기 보안 업데이트 권고

행 취약성 Microsoft Office CVE-2021-34451 Microsoft Office Online Server 스푸핑 취약성 Microsoft Office Excel CVE-2021-34518 Microsoft Excel 원격 코드 실행 취약성 Microsoft Office Excel CVE-2021-34501 Microsoft Excel 원격 코드 실행 취약성 Microsoft Office SharePoint CVE-2021-34520 Microsoft SharePoint Server 원격 코드 실행 취약성 Microsoft Office SharePoint CVE-2021-34519 Microsoft SharePoint Server 정보 유출 취약성 Microsoft Office SharePoint CVE-2021-34517 Microsoft SharePoint Server 스푸핑 취약성 Microsoft Office SharePoint CVE-2021-34468 Microsoft SharePoint Server 원격 코드 실행 취약성 Microsoft Office SharePoint CVE-2021-34467 Microsoft SharePoint Server 원격 코드 실행 취약성 Microsoft Scripting Engine CVE-2021-34448 스크립팅 엔진 메모리 손상 취약성 Microsoft Windows Codecs Library CVE-2021-34521 Raw Image Extension Remote Code Execution Vulnerability Microsoft Windows Codecs Library CVE-2021-33778 HEVC 비디오 확장 원격 코드 실행 취약성 Microsoft Windows Codecs Library CVE-2021-33777 HEVC 비디오 확장 원격 코드 실행 취약성 Microsoft Windows Codecs Library CVE-2021-33776 HEVC 비디오 확장 원격 코드 실행 취약성 Microsoft Windows Codecs Library CVE-2021-33775 HEVC 비디오 확장 원격 코드 실행 취약성 Microsoft Windows Codecs Library CVE-2021-33760 미디어 파운데이션 정보 유출 취약성 Microsoft Windows Codecs Library CVE-2021-33740 Windows Media 원격 코드 실행 취약성 Microsoft Windows Codecs Library CVE-2021-31947 HEVC 비디오 확장 원격 코드 실행 취약성 Microsoft Windows

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 16 Jul 2021 · Last source change 10 Aug 2026, 15:11 UTC · CWE-787 · Out-of-bounds Write

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-21103
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    10.0.10240.0 < 10.0.10240.19003; 10.0.14393.0 < 10.0.14393.4530; 10.0.17763.0 < 10.0.17763.2061; 10.0.0 < 10.0.17763.2061; 10.0.0 < 10.0.18363.1679; 10.0.0 < 10.0.19041.1110; 10.0.0 < 10.0.19042.1110; 10.0.0 < 10.0.19043.1110 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    Windows 10 Version 1507: 10.0.10240.0 < 10.0.10240.19003; Windows 10 Version 1607: 10.0.14393.0 < 10.0.14393.4530; Windows 10 Version 1809: 10.0.17763.0 < 10.0.17763.2061, 10.0.0 < 10.0.17763.2061; Windows 10 Version 1909: 10.0.0 < 10.0.18363.1679; Windows 10 Version 2004: 10.0.0 < 10.0.19041.1110; Windows 10 Version 20H2: 10.0.0 < 10.0.19042.1110; Windows 10 Version 21H1: 10.0.0 < 10.0.19043.1110; Windows 7: 6.1.0 < 6.1.7601.25661; Windows 7 Service Pack 1: 6.1.0 < 6.1.7601.25661; Windows 8.1: 6.3.0 < 6.3.9600.20069; Windows Server 2008 R2 Service Pack 1: 6.1.7601.0 < 6.1.7601.25661; Windows Server 2012: 6.2.9200.0 < 6.2.9200.23409; Windows Server 2012 R2: 6.3.9600.0 < 6.3.9600.20069; Windows Server 2016: 10.0.14393.0 < 10.0.14393.4530; Windows Server 2019: 10.0.17763.0 < 10.0.17763.2061 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-21103↗CISA KEV record↗CVE authority or vendor reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-34448 · cve.blacktree.nl