CVE-2021-1721Network attack vector

Denial of service via malformed runtime input

Published Feb 25, 2021 · Updated May 28, 2026

Denial-of-service vulnerability in Microsoft .NET Core and Visual Studio allows attackers to interrupt service via crafted input. The affected parsing or processing locus is not publicly disclosed by Microsoft, so the precise malformed-input operation cannot be named. The CVSS record requires user interaction, and the bounded consequence is service unavailability without confidentiality or integrity impact.

CVSS severity6.5
Medium
EPSS probability3.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial-of-service vulnerability in Microsoft .NET Core and Visual Studio allows attackers to interrupt service via crafted input. The affected parsing or processing locus is not publicly disclosed by Microsoft, so the precise malformed-input operation cannot be named. The CVSS record requires user interaction, and the bounded consequence is service unavailability without confidentiality or integrity impact.

The record

CVE
CVE-2021-1721
Published
Feb 25, 2021
Updated
May 28, 2026
Vendor
Microsoft
Product
Microsoft Visual Studio 2019
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 25, 2021CVE publishedPublication date reported by the CVE source.
  2. May 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.0.0 <publication
  2. Affected versionversion=16.0 <publication

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Visual Studio 2019version=16.0.0 <publication; version=16.0 <publication
Microsoft · .NET Core 2.1version=2.1 <publication
Microsoft · PowerShell 7.1version=7.1.0 <publication
Microsoft · .NET Core 3.1version=3.1 <publication
Microsoft · PowerShell 7.0version=7.0.0 <publication
Microsoft · Microsoft Visual Studio 2017version=15.9.0 <publication
Microsoft · .NET 5.0version=5.0.0 <publication

Published CVSS scores

4.3NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
6.5MicrosoftCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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