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Fencer Vulns
critical 9.8

CVE-2021-26701 in the critical feed json

.NET Core Remote Code Execution Vulnerability

published 2021-02-25 5 y ago modified 2026-09-08 2 mo ago also BIT-dotnet-2021-26701 , BIT-dotnet-sdk-2021-26701 , EUVD-2021-0826 , GHSA-ghhp-997w-qr28

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
30.1%
EPSS 30.1% chance of exploitation in 30 days, percentile 98%
public exploits
0
none known

Summary

.NET Core Remote Code Execution Vulnerability

Patch / fix

  • nuget System.Text.Encodings.Web 4.5.1, 4.7.2, 5.0.1
  • bitnami dotnet 5.0.4
  • bitnami dotnet-sdk 5.0.4
  • microsoft .net 5.0.4
  • microsoft .net_core 2.1.28, 3.1.15
  • rh-dotnet31-dotnet RHEL 3.1 DOTNET 3.1.113-1.el7_9
  • rh-dotnet31-dotnet-host RHEL 3.1 DOTNET 3.1.13-1.el7_9
  • rh-dotnet31-dotnet-sdk-3.1 RHEL 3.1 DOTNET 3.1.113-1.el7_9
  • rh-dotnet31-dotnet-hostfxr-3.1 RHEL 3.1 DOTNET 3.1.13-1.el7_9
  • rh-dotnet31-dotnet-runtime-3.1 RHEL 3.1 DOTNET 3.1.13-1.el7_9
  • rh-dotnet31-dotnet-templates-3.1 RHEL 3.1 DOTNET 3.1.113-1.el7_9
  • rh-dotnet31-aspnetcore-runtime-3.1 RHEL 3.1 DOTNET 3.1.13-1.el7_9
  • rh-dotnet31-dotnet-apphost-pack-3.1 RHEL 3.1 DOTNET 3.1.13-1.el7_9

red hat advisories RHSA-2021:0789RHSA-2021:0790RHSA-2021:0787RHSA-2021:0788RHSA-2021:0794RHSA-2021:0793

  • dotnet-sdk Arch Linux 5.0.4.sdk104-1
  • dotnet-runtime Arch Linux 5.0.4.sdk104-1

arch linux advisories AVG-1698

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-26701 updated cvss 8.1

dotnet: System.Text.Encodings.Web Remote Code Execution

  • Red Hat .NET Core on Red Hat Enterprise Linux ComputeNode (v. 7) rh-dotnet21 2.1-25.el7_9, rh-dotnet21-runtime 2.1-25.el7_9, rh-dotnet21-dotnet 2.1.522-1.el7_9, rh-dotnet31-dotnet 3.1.113-1.el7_9, rh-dotnet50-dotnet 5.0.104-1.el7_9, rh-dotnet50-dotnet-host 5.0.4-1.el7_9, +23 more Red Hat .NET Core on Red Hat Enterprise Linux Server (v. 7) rh-dotnet21 2.1-25.el7_9, rh-dotnet21-runtime 2.1-25.el7_9, rh-dotnet21-dotnet 2.1.522-1.el7_9, rh-dotnet31-dotnet 3.1.113-1.el7_9, rh-dotnet50-dotnet 5.0.104-1.el7_9, rh-dotnet50-dotnet-host 5.0.4-1.el7_9, +23 more Red Hat .NET Core on Red Hat Enterprise Linux Workstation (v. 7) rh-dotnet21 2.1-25.el7_9, rh-dotnet21-runtime 2.1-25.el7_9, rh-dotnet21-dotnet 2.1.522-1.el7_9, rh-dotnet31-dotnet 3.1.113-1.el7_9, rh-dotnet50-dotnet 5.0.104-1.el7_9, rh-dotnet50-dotnet-host 5.0.4-1.el7_9, +23 more
    fixed: vendor fix RHSA-2021:0787
  • Red Hat Enterprise Linux AppStream (v. 8) dotnet 2.1.522-1.el8_3, dotnet 5.0.104-1.el8_3, dotnet-host 5.0.4-1.el8_3, dotnet3.1 3.1.113-1.el8_3, dotnet5.0 5.0.104-1.el8_3, dotnet-sdk-2.1 2.1.522-1.el8_3, +20 more
    fixed: vendor fix RHSA-2021:0790

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2 y ago

Exploit prediction

30.10% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 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
GitHub 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
OSV 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
nuget System.Text.Encodings.Web
>=4.0.0, <4.5.1
>=4.6.0, <4.7.2
>=5.0.0, <5.0.1
4.5.1
4.7.2
5.0.1
bitnami dotnet
>=5.0.0, <5.0.4
5.0.4
bitnami dotnet-sdk
>=5.0.0, <5.0.4
5.0.4

Affected products

  • Microsoft .NET Core 2.1
  • Microsoft .NET Core 3.1
  • Microsoft .NET 5.0
  • Microsoft Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3)
  • Microsoft Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8)
  • Microsoft Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6)
  • Microsoft Visual Studio 2019 for Mac
  • Microsoft Microsoft Visual Studio 2019 version 16.8 (includes 16.0 - 16.7)
  • Microsoft Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8)
  • Microsoft PowerShell Core 7.1
  • Microsoft PowerShell Core 7.0

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.