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Full vulnerability report · 2021
CVE-2021-26893High confidence

Windows DNS Server Remote Code Execution Vulnerability

Microsoft · Windows Server 2008 R2 Service Pack 1

9.8CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 7.02% 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.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Microsoft Windows Server 2008 R2 Service Pack 1 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-2021-13677

No EUVD known-exploited evidence

Windows DNS Server Remote Code Execution Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
9.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

Windows DNS Server Remote Code Execution Vulnerability

What

Windows DNS Server Remote Code Execution Vulnerability

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

What

Windows DNS Server Remote Code Execution Vulnerability

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

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.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

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 → vulnerable operation → execute code or commands in the affected security context
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration.
CWE not yet assigned
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:N/S:U/C:H/I:H/A:H/E:U/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.UINoneUser interaction: No action by another user is required.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.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
NetworkUnauthenticatedRemote code execution
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-13677Official EUVD mapping

Windows DNS Server Remote Code Execution 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-181Multiples vulnérabilités dans Microsoft Windows

d?id=CVE-2021-26882 Référence CVE CVE-2021-26884 https://www.cve.org/CVERecord?id=CVE-2021-26884 Référence CVE CVE-2021-26885 https://www.cve.org/CVERecord?id=CVE-2021-26885 Référence CVE CVE-2021-26886 https://www.cve.org/CVERecord?id=CVE-2021-26886 Référence CVE CVE-2021-26887 https://www.cve.org/CVERecord?id=CVE-2021-26887 Référence CVE CVE-2021-26889 https://www.cve.org/CVERecord?id=CVE-2021-26889 Référence CVE CVE-2021-26890 https://www.cve.org/CVERecord?id=CVE-2021-26890 Référence CVE CVE-2021-26891 https://www.cve.org/CVERecord?id=CVE-2021-26891 Référence CVE CVE-2021-26892 https://www.cve.org/CVERecord?id=CVE-2021-26892 Référence CVE CVE-2021-26893 https://www.cve.org/CVERecord?id=CVE-2021-26893 Référence CVE CVE-2021-26894 https://www.cve.org/CVERecord?id=CVE-2021-26894 Référence CVE CVE-2021-26895 https://www.cve.org/CVERecord?id=CVE-2021-26895 Référence CVE CVE-2021-26896 https://www.cve.org/CVERecord?id=CVE-2021-26896 Référence CVE CVE-2021-26897 https://www.cve.org/CVERecord?id=CVE-2021-26897 Référence CVE CVE-2021-26898 https://www.cve.org/CVERecord?id=CVE-2021-26898 Référence CVE CVE-2021-26899 https://www.cve.org/CVERecord?id=CVE-2021-26899 Référence CVE CVE-2021-26900 https://www.cve.org/CVERecord?id=CVE-2021-26900 Référence CVE CVE-2021-26901 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001272Microsoft Windows Server におけるリモートでコードを実行される脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-26877、CVE-2021-26893、CVE-2021-26894、CVE-2021-26897 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001271Microsoft Windows Server におけるリモートでコードを実行される脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-26893、CVE-2021-26894、CVE-2021-26895、CVE-2021-26897 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001261Microsoft Windows Server におけるリモートでコードを実行される脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-26877、CVE-2021-26893、CVE-2021-26894、CVE-2021-26895 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001232Microsoft Windows Server におけるリモートでコードを実行される脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-26877、CVE-2021-26893、CVE-2021-26895、CVE-2021-26897 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001231Microsoft Windows Server におけるリモートでコードを実行される脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-26877、CVE-2021-26894、CVE-2021-26895、CVE-2021-26897 とは異なる脆弱性です。

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

취약성 CVE-2021-27051 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-27050 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-27049 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-27048 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-27047 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-26902 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-26884 Windows Media 사진 코덱 정보 유출 취약성 CVE-2021-24110 HEVC 비디오 확장 원격 코드 실행 취약성 CVE-2021-24089 HEVC 비디오 확장 원격 코드 실행 취약성 Power BI CVE-2021-26859 Microsoft Power BI 정보 유출 취약성 Role: DNS Server CVE-2021-27063 Windows DNS 서버 서비스 거부 취약성 CVE-2021-26897 Windows DNS 서버 원격 코드 실행 취약성 CVE-2021-26896 Windows DNS 서버 서비스 거부 취약성 CVE-2021-26895 Windows DNS 서버 원격 코드 실행 취약성 CVE-2021-26894 Windows DNS 서버 원격 코드 실행 취약성 CVE-2021-26893 Windows DNS 서버 원격 코드 실행 취약성 CVE-2021-26877 Windows DNS 서버 원격 코드 실행 취약성 CVE-2021-26879 Windows NAT 서비스 거부 취약성 CVE-2021-26867 Windows Hyper-V 원격 코드 실행 취약성 Visual Studio CVE-2021-21300 Visual Studio용 Git 원격 코드 실행 취약성 CVE-2021-27084 Visual Studio Code Java 확장 팩 원격 코드 실행 취약성 CVE-2021-27083 Visual Studio Code용 원격 개발 확장 원격 코드 실행 취약성 CVE-2021-27082 Visual Studio Code용 Microsoft Quantum 개발 키트 원격 코드 실행 취약성 CVE-2021-27081 Visual Studio Code ESLint 확장 원격 코드 실행 취약성 CVE-2021-27060 Visual Studio Code 원격 코드 실행 취약성 Windows Admin Center CVE-2021-27066 Windows 관리 센터 보안 기능 우회 취약성 CVE-2021-26891 Windows 컨테이너 실행 에이전트 권한 상승 취약성 CVE-2021-26865 Windows 컨테이너 실행 에이전트

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 19 Aug 2026, 16:30 UTC · CWE not yet assigned

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-2021-13677
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceUnavailable
NVD statusNVD modified after enrichment

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added remediation: portal.msrc.microsoft.com/CVE-2021-26893; removed patch: msrc.microsoft.com/CVE-2021-26893; removed remediation: msrc.microsoft.com/CVE-2021-26893.
    Before
    patch: msrc.microsoft.com/CVE-2021-26893 · patch: portal.msrc.microsoft.com/CVE-2021-26893 · remediation: msrc.microsoft.com/CVE-2021-26893
    After
    patch: portal.msrc.microsoft.com/CVE-2021-26893 · remediation: portal.msrc.microsoft.com/CVE-2021-26893
    portal.msrc.microsoft.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added patch: msrc.microsoft.com/CVE-2021-26893; added remediation: msrc.microsoft.com/CVE-2021-26893; removed remediation: portal.msrc.microsoft.com/CVE-2021-26893.
    Before
    patch: portal.msrc.microsoft.com/CVE-2021-26893 · remediation: portal.msrc.microsoft.com/CVE-2021-26893
    After
    patch: msrc.microsoft.com/CVE-2021-26893 · patch: portal.msrc.microsoft.com/CVE-2021-26893 · remediation: msrc.microsoft.com/CVE-2021-26893
    msrc.microsoft.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    10.0.0 < publication; 6.0.0 < 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
    6.1.7601.0 < 6.1.7601.24566; 6.0.6003.0 < 6.0.6003.21070; 6.2.9200.0 < 6.2.9200.23298; 6.3.9600.0 < 6.3.9600.19968 · 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
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-13677↗Patch or update reference↗CVE authority or vendor 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-2021-26893 · cve.blacktree.nl