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Full vulnerability report · 2021
CVE-2021-34499High confidence

Windows DNS Server Denial of Service Vulnerability

Microsoft · Windows Server 2008 R2 Service Pack 1

6.5MediumCVSS 3.1
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 2.87% 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: As exposure requiresRemediation target: Within 365 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-2021-21153

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

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
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

Windows DNS Server Denial of Service Vulnerability

What

Windows DNS Server Denial of Service 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 with low privileges. If successful, the issue may disrupt the affected service.

What

Windows DNS Server Denial of Service 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 with low privileges. If successful, the issue may disrupt the affected service.

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 → disrupt the affected service
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
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:L/UI:N/S:U/C:N/I:N/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.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major 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.
NetworkDenial of service
A

Official authority intelligence

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

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-2021-34489 Référence CVE CVE-2021-34490 https://www.cve.org/CVERecord?id=CVE-2021-34490 Référence CVE CVE-2021-34491 https://www.cve.org/CVERecord?id=CVE-2021-34491 Référence CVE CVE-2021-34492 https://www.cve.org/CVERecord?id=CVE-2021-34492 Référence CVE CVE-2021-34493 https://www.cve.org/CVERecord?id=CVE-2021-34493 Référence CVE CVE-2021-34494 https://www.cve.org/CVERecord?id=CVE-2021-34494 Référence CVE CVE-2021-34496 https://www.cve.org/CVERecord?id=CVE-2021-34496 Référence CVE CVE-2021-34497 https://www.cve.org/CVERecord?id=CVE-2021-34497 Référence CVE CVE-2021-34498 https://www.cve.org/CVERecord?id=CVE-2021-34498 Référence CVE CVE-2021-34499 https://www.cve.org/CVERecord?id=CVE-2021-34499 Référence CVE CVE-2021-34500 https://www.cve.org/CVERecord?id=CVE-2021-34500 Référence CVE CVE-2021-34503 https://www.cve.org/CVERecord?id=CVE-2021-34503 Référence CVE CVE-2021-34504 https://www.cve.org/CVERecord?id=CVE-2021-34504 Référence CVE CVE-2021-34507 https://www.cve.org/CVERecord?id=CVE-2021-34507 Référence CVE CVE-2021-34508 https://www.cve.org/CVERecord?id=CVE-2021-34508 Référence CVE CVE-2021-34509 https://www.cve.org/CVERecord?id=CVE-2021-34509 Référence CVE CVE-2021-34510 https://www.cve.org/CVERecord?id=CVE-2021-34510 Référence CVE CVE-2021-34511 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002252Microsoft Windows Server におけるサービス運用妨害 (DoS) の脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、サービス運用妨害 (DoS) の脆弱性が存在します。 本脆弱性は、CVE-2021-33745、CVE-2021-34444、CVE-2021-34499 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002253Microsoft Windows Server におけるサービス運用妨害 (DoS) の脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、サービス運用妨害 (DoS) の脆弱性が存在します。 本脆弱性は、CVE-2021-33745、CVE-2021-34442、CVE-2021-34499 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002133Microsoft Windows Server におけるサービス運用妨害 (DoS) の脆弱性

Microsoft Windows Server には、Windows DNS サーバに不備があるため、サービス運用妨害 (DoS) の脆弱性が存在します。 本脆弱性は、CVE-2021-33745、CVE-2021-34442、CVE-2021-34444 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002118Windows Server におけるサービス運用妨害 (DoS) の脆弱性

Windows Server には、Windows DNS サーバに不備があるため、サービス運用妨害 (DoS) の脆弱性が存在します。 本脆弱性は、CVE-2021-34442、CVE-2021-34444、CVE-2021-34499 とは異なる脆弱性です。

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

팅 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 DNS CVE-2021-34499 Windows DNS 서버 서비스 거부 취약성 Microsoft Windows DNS CVE-2021-33754 Windows DNS 서버 원격 코드 실행 취약성 Microsoft Windows DNS CVE-2021-33746 Windows DNS 서버 원격 코드 실행 취약성 Microsoft Windows Media Foundation CVE-2021-34503 Windows 미디어 파운데이션 원격 코드 실행 취약성 Microsoft Windows Media Foundation CVE-2021-34441 Windows 미디어 파운데이션 원격 코드 실행 취약성 Microsoft Windows Media Foundation CVE-2021-34439 Windows 미디어 파운데이션 원격 코드 실행 취약성 OpenEnclave CVE-2021-33767 Open Enclave SDK 권한 상승 취약성 Power BI CVE-2021-31984 Windows BI 원격 코드 실행 취약성 Role: DNS Server CVE-2021-34525 Windows DNS 서버 원격 코드 실행 취약성 Role: DNS Server CVE-2021-34494 Windows DNS 서버 원격 코드 실행 취약성 Role: DNS Server CVE-2021-34

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 14 Jul 2021 · Last source change 10 Aug 2026, 15:11 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-2021-21153
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 ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

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-2021-21153↗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-2021-34499 · cve.blacktree.nl