9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2021-26701

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

.NET Core Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-24112.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 5.0, .NET Core 3.1, and .NET Core 2.1. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A remote code execution vulnerability exists in .NET 5 and .NET Core due to how text encoding is performed.

Discussion

Discussion for this issue can be found at dotnet/runtime#49377

Mitigation factors

Microsoft has not identified any mitigating factors for this vulnerability.

Affected software

The vulnerable package is System.Text.Encodings.Web . Upgrading your package and redeploying your app should be sufficient to address this vulnerability.

Vulnerable package versions:

Any .NET 5, .NET Core, or .NET Framework based application that uses the System.Text.Encodings.Web package with a vulnerable version listed below.

Package Name | Vulnerable Versions | Secure Versions -|-|- System.Text.Encodings.Web | 4.0.0 - 4.5.0 | 4.5.1 System.Text.Encodings.Web | 4.6.0-4.7.1 | 4.7.2 System.Text.Encodings.Web | 5.0.0 | 5.0.1

Please validate that each of the .NET versions you are using is in support. Security updates are only provided for supported .NET versions.

(GitHub Advisory)

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CVE-2021-26701

CVE-2021-26701:

9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
System.Text.Encodings.Web	nuget	>= 4.0.0, < 4.5.1	4.5.1
System.Text.Encodings.Web	nuget	>= 4.6.0, < 4.7.2	4.7.2
System.Text.Encodings.Web	nuget	= 5.0.0	5.0.1

Technical Details

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Root Cause Analysis

The vulnerability exists in System.Text.Encodings.Web package's text encoding implementation. While specific code patches are not shown, the security advisory explicitly states the RCE occurs 'due to how text encoding is performed'. The core TextEncoder.Encode method is responsible for output encoding across all derived encoders. Improper escaping in this method would allow payloads to bypass sanitization. The patched versions (4.5.1/4.7.2/5.0.1) likely contain fixes in these encoding primitives. Runtime detection would focus on encoding entry points handling user-controlled input.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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9.8

-

Basic Information

Basic Information

Concerned about an active attack path?

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

Executive summary

Discussion

Mitigation factors

Affected software

CVE-2021-26701:

9.8

-

Basic Information

Basic Information

Is this CVE running in your environment?

Technical Details

Technical Details

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Root Cause Analysis

Vulnerable functions

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WAF Protection Rules

WAF Rule

Reasoning

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Root Cause Analysis

Vulnerable functions

Technical Details

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

Executive summary

Discussion

Mitigation factors

Affected software

9.8

9.8

Basic Information

Basic Information

Vulnerability Intelligence
Miggo AI

Vulnerability Intelligence
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