.NET Core Remote Code Execution Vulnerability

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2021-26701: 30.10% estimated exploitation activity in the next 30 days; percentile 98.22 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

.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.…

Published by the source

21 Apr 2021, 19:38 UTC

Last modified by the source

7 Jan 2024, 05:05 UTC

Source last checked

26 Oct 2026, 17:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-ghhp-997w-qr28

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# Patch Next advisory brief: CVE-2021-26701

Advisory: .NET Core Remote Code Execution Vulnerability
IDs: CVE-2021-26701, GHSA-ghhp-997w-qr28
Record: https://patchnext.com/advisories/cve-2021-26701 (revision 1, source checked 26 Oct 2026, 17:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: system.text.encodings.web 5.0.1, 4.7.2, 4.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet system.text.encodings.web: affected >= 4.0.0, < 4.5.1; >= 4.6.0, < 4.7.2; >= 5.0.0, <= 5.0.0; fixed in 4.5.1, 5.0.1, 4.7.2

## Suggested inspection (read-only)
- NuGet system.text.encodings.web: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on system.text.encodings.web.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-ghhp-997w-qr28 (GitHub-reviewed advisory GHSA-ghhp-997w-qr28 lists affected ranges: NuGet system.text.encodings.web >=4.0.0 =4.6.0 =5.0.0 <=5.0.0)

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