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Full vulnerability report · 2021
CVE-2021-26411High confidence

Microsoft Internet Explorer Memory Corruption Vulnerability

Microsoft · Internet Explorer

8.8HighCVSS 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 severityHighOperational priority:Critical, raised one band.upgradedsince 3 Nov 2021

Evidence used

  • CISA confirms exploitation in the wild.
  • EPSS is 80.77% 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 Internet Explorer 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-2021-13217

CISA KEV mirrored by ENISA

Internet Explorer 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
8.8 · 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 Internet Explorer contains an unspecified vulnerability that allows for memory corruption.

What

Microsoft Internet Explorer contains an unspecified vulnerability that allows for memory corruption.

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

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 Internet Explorer contains an unspecified vulnerability that allows for memory corruption.

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

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. Known ransomware campaign use is recorded.

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 → Use After Free → 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
Low: no specialised conditions are recorded
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-416 ↗

CWE-416: Use After Free. The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

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:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SChangedScope: The attack can affect a component governed by a different security authority.CLowConfidentiality impact: A successful attack can cause a limited loss.IHighIntegrity impact: A successful attack can cause a major loss.ALowAvailability impact: A successful attack can cause a limited loss.
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-416CISA KEV
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-13217Known-exploited evidence recorded

Internet Explorer Memory Corruption Vulnerability

Official EUVD record ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210317Security Bulletin 17 Mar 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 17 Mar 2021, published on 17 March 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-179Vulnérabilité dans Microsoft Edge

Une vulnérabilité a été corrigée dans Microsoft Edge . Elle permet à un attaquant de provoquer une exécution de code à distance.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-178Multiples vulnérabilités dans Microsoft IE

De multiples vulnérabilités ont été corrigées dans Microsoft IE . Elles permettent à un attaquant de provoquer une exécution de code à distance.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001268複数の Microsoft 製品におけるメモリ破損の脆弱性

Microsoft Internet Explorer 9、11、Microsoft Edge には、メモリ破損の脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5282MS 3월 보안 위협에 따른 정기 보안 업데이트 권고

ual Studio 관련 소프트웨어 긴급 원격 코드 실행 - Windows 관리 센터 중요 보안 기능 우회 - HEVC 비디오 확장 긴급 원격 코드 실행 - [참고 사이트] [1] (한글) https://portal.msrc.microsoft.com/ko-kr/security-guidance [2] (영문) https://portal.msrc.microsoft.com/en-us/security-guidance [3] https://msrc.microsoft.com/update-guide/releaseNote/2021-Mar o 취약점 요약 정보 제품 카테고리 CVE 번호 CVE 제목 .NET Core CVE-2021-26701 .NET Core 원격 코드 실행 취약성 Application Virtualization CVE-2021-26890 응용 프로그램 가상화 원격 코드 실행 취약성 Azure CVE-2021-27075 Azure 가상 컴퓨터 정보 유출 취약성 Azure Sphere CVE-2021-27080 Azure Sphere 미서명 코드 실행 취약성 CVE-2021-27074 Azure Sphere 미서명 코드 실행 취약성 Internet Explorer CVE-2021-27085 Internet Explorer 원격 코드 실행 취약성 CVE-2021-26411 Internet Explorer 메모리 손상 취약성 Microsoft ActiveX CVE-2021-26869 Windows ActiveX 설치 관리자 서비스 정보 유출 취약성 Microsoft Exchange Server CVE-2021-27065 Microsoft Exchange Server 원격 코드 실행 취약성 CVE-2021-26858 Microsoft Exchange Server 원격 코드 실행 취약성 CVE-2021-26857 Microsoft Exchange Server 원격 코드 실행 취약성 CVE-2021-26855 Microsoft Exchange Server 원격 코드 실행 취약성 Microsoft Graphics Component CVE-2021-27077 Windows Win32k 권한 상승 취약성 CVE-2021-26876 OpenType 글꼴 구문 분석 원격 코드 실행 취약성 CVE-2021-26875 Windows Win32k 권한 상승 취약성 CVE-2021-26868 Windows 그래픽 구성 요소 권한 상승 취약성 CVE-2021-26863 Windows Win32k 권한 상승 취약성 CVE-2021-26861 Windows 그래픽 구성 요소 원격 코드 실행 취약성 Microsoft Office CVE-202

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 11 Mar 2021 · Last source change 1 Oct 2026, 20:31 UTC · CWE-416 · Use After Free

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-2021-13217
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
    1.0.0 < 10.0.17134.2087; 1.0.0 < 6.0.6003.21070; 1.0..0 < 10.0.17134.2087 · 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
    Internet Explorer 11: 1.0.0 < 10.0.17134.2087; Internet Explorer 9: 1.0.0 < 6.0.6003.21070; Microsoft Edge (EdgeHTML-based): 1.0..0 < 10.0.17134.2087 · 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 ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added patch: msrc.microsoft.com/CVE-2021-26411; added remediation: msrc.microsoft.com/CVE-2021-26411; removed remediation: portal.msrc.microsoft.com/CVE-2021-26411.
    Before
    patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: portal.msrc.microsoft.com/CVE-2021-26411
    After
    patch: msrc.microsoft.com/CVE-2021-26411 · patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: msrc.microsoft.com/CVE-2021-26411
    secure@microsoft.com ↗
  3. Vendor guidanceAuthoritative vendor guidance changed: added remediation: portal.msrc.microsoft.com/CVE-2021-26411; removed patch: msrc.microsoft.com/CVE-2021-26411; removed remediation: msrc.microsoft.com/CVE-2021-26411.
    Before
    patch: msrc.microsoft.com/CVE-2021-26411 · patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: msrc.microsoft.com/CVE-2021-26411
    After
    patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: portal.msrc.microsoft.com/CVE-2021-26411
    portal.msrc.microsoft.com ↗
  4. Vendor guidanceAuthoritative vendor guidance changed: added patch: msrc.microsoft.com/CVE-2021-26411; added remediation: msrc.microsoft.com/CVE-2021-26411; removed remediation: portal.msrc.microsoft.com/CVE-2021-26411.
    Before
    patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: portal.msrc.microsoft.com/CVE-2021-26411
    After
    patch: msrc.microsoft.com/CVE-2021-26411 · patch: portal.msrc.microsoft.com/CVE-2021-26411 · remediation: msrc.microsoft.com/CVE-2021-26411
    msrc.microsoft.com ↗
  5. Affected versionsThe structured affected or fixed version information changed.
    Before
    1.0.0 < publication; 1.0..0 < publication · 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
    1.0.0 < 10.0.17134.2087; 1.0.0 < 6.0.6003.21070; 1.0..0 < 10.0.17134.2087 · 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-2021-13217↗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-2021-26411 · cve.blacktree.nl