BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2021
CVE-2021-26423High confidence

.NET Core and Visual Studio Denial of Service Vulnerability

Microsoft · .NET 5.0

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, 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 3.90% 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 .NET 5.0 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 30 daysRemediation target: Within 180 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.

Open-source package ranges33 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.AOT.linux-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.AOT.osx-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.linux-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.linux-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.LLVM.osx-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.linux-armECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.linux-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.linux-musl-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.linux-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.Mono.osx-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-armECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-armECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-arm64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-musl-armECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-musl-arm64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-musl-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-musl-x64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-musl-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-x64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.linux-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.osx-x64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.osx-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.rhel.6-x64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-armECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-armECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-arm64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-arm64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-x64ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-x64ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-x86ECOSYSTEM: introduced 3.1.0; fixed 3.1.183.1.18OSV record ↗aggregator derived · 1 Dec 2024
NuGetMicrosoft.NETCore.App.Runtime.win-x86ECOSYSTEM: introduced 5.0.0; fixed 5.0.95.0.9OSV record ↗aggregator derived · 1 Dec 2024
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-2022-7160

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 actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

.NET Core and Visual Studio Denial of Service Vulnerability

What

.NET Core and Visual Studio 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 without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

.NET Core and Visual Studio 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 without authentication or user interaction. 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
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: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.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.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.
NetworkUnauthenticatedDenial 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-20210818Security Bulletin 18 Aug 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 18 Aug 2021, published on 18 August 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-620Multiples vulnérabilités dans les produits Microsoft

De multiples vulnérabilités ont été corrigées dans les produits Microsoft . Elles permettent à un attaquant de provoquer une élévation de privilèges, une exécution de code à distance, une atteinte à la confidentialité des données, un déni de service et une usurpation d'identité.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-619Multiples vulnérabilités dans Microsoft .Net

De multiples vulnérabilités ont été corrigées dans Microsoft .Net . Elles permettent à un attaquant de provoquer un déni de service et une atteinte à la confidentialité des données.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002313複数の Microsoft 製品におけるサービス運用妨害 (DoS) の脆弱性

複数の Microsoft 製品には、サービス運用妨害 (DoS) の脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5362MS 8월 보안 위협에 따른 정기 보안 업데이트 권고

Point 관련 소프트웨어 중요 스푸핑 4011600, 5002000, 5002002 Microsoft Visual Studio 관련 소프트웨어 중요 정보 유출 MS 업데이트 페이지 참고 [4] Microsoft Dynamics 관련 소프트웨어 중요 원격 코드 실행 Microsoft .NET 관련 소프트웨어 중요 정보 유출 Microsoft Azure 관련 소프트웨어 중요 권한 상승 Microsoft Malware Protection Engine 중요 권한 상승 [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-Aug [4] https://msrc.microsoft.com/update-guide o 취약점 요약 정보 제품 카테고리 CVE 번호 CVE 제목 .NET Core & Visual Studio CVE-2021-34485 .NET Core 및 Visual Studio 정보 공개 취약성 .NET Core & Visual Studio CVE-2021-26423 .NET Core 및 Visual Studio 서비스 거부 취약성 ASP.NET Core & Visual Studio CVE-2021-34532 ASP.NET Core 및 Visual Studio 정보 공개 취약성 Azure CVE-2021-36943 Azure CycleCloud 권한 상승 취약성 Azure CVE-2021-33762 Azure CycleCloud 권한 상승 취약성 Azure Sphere CVE-2021-26430 Azure Sphere 서비스 거부 취약성 Azure Sphere CVE-2021-26429 Azure Sphere 권한 상승 취약성 Azure Sphere CVE-2021-26428 Azure Sphere 정보 유출 취약성 Microsoft Azure Active Directory Connect CVE-2021-36949 Microsoft Azure Active Directory 연결 인증 우회 취약성 Microsoft Dynamics CVE-2021-36950 Microsoft Dynamics 365(온-프레미스) 교차-사이트 스크립팅 취약성 Microsoft Dynamics CVE-2021-36946 Microsoft Dynamics Business Central 교차-사이트 스크립팅 취약성 Microsoft

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 12 Aug 2021 · Last source change 10 Aug 2026, 15:09 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-2022-7160
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-2022-7160↗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-2021-26423 · cve.blacktree.nl