.NET Framework September 2020 Security and Quality Rollup Updates

Tara Overfield


Today, we are releasing the September 2020 Security and Quality Rollup Updates for .NET Framework.


ClickOnce will no longer download applications from untrusted servers which use NTLM authentication, but, instead, will fail with “Authentication failed”. Sites in the Local Intranet and Trusted sites zones will continue to authenticate as before.

Quality and Reliability

This release contains the following quality and reliability improvements.

  • Addresses an issue in some 32 bit apps where, in certain scenarios, the JIT might omit a function call
  • Improved support for cleaning up private temporary certificate keys
  • Addresses an issue with a null-reference crash in automation code, arising from re-entrancy when reconnection to a remote desktop

1 Common Language Runtime (CLR) 2 Windows Presentation Foundation (WPF)

Getting the Update

The Security and Quality Rollup is available via Windows Update, Windows Server Update Services, and Microsoft Update Catalog. The Security Only Update is available via Windows Server Update Services and Microsoft Update Catalog.

Microsoft Update Catalog

You can get the update via the Microsoft Update Catalog. For Windows 10, NET Framework 4.8 updates are available via Windows Update, Windows Server Update Services, Microsoft Update Catalog. Updates for other versions of .NET Framework are part of the Windows 10 Monthly Cumulative Update.

**Note**: Customers that rely on Windows Update and Windows Server Update Services will automatically receive the .NET Framework version-specific updates. Advanced system administrators can also take use of the below direct Microsoft Update Catalog download links to .NET Framework-specific updates. Before applying these updates, please ensure that you carefully review the .NET Framework version applicability, to ensure that you only install updates on systems where they apply.

The following table is for Windows 10 and Windows Server 2016+ versions.

Product VersionCumulative Update
Windows 10 Version Next and Windows Server, Version Next
.NET Framework 3.5, 4.8Catalog4576477
Windows 10 2004 and Windows Server, version 2004
.NET Framework 3.5, 4.8Catalog4576478
Windows 10 1909 and Windows Server, version 1909
.NET Framework 3.5, 4.8Catalog4576484
Windows 10 1903 and Windows Server, version 1903
.NET Framework 3.5, 4.8Catalog4576484
Windows 10 1809 (October 2018 Update) and Windows Server 20194576627
.NET Framework 3.5, 4.7.2Catalog4570720
.NET Framework 3.5, 4.8Catalog4576483
Windows 10 1803 (April 2018 Update)
.NET Framework 3.5, 4.7.2Catalog4577032
.NET Framework 4.8Catalog4576482
Windows 10 1709 (Fall Creators Update)
.NET Framework 3.5, 4.7.1, 4.7.2Catalog4577041
.NET Framework 4.8Catalog4576481
Windows 10 1703 (Creators Update)
.NET Framework 3.5, 4.7, 4.7.1, 4.7.2Catalog4577021
.NET Framework 4.8Catalog4576480
Windows 10 1607 (Anniversary Update) and Windows Server 2016
.NET Framework 3.5, 4.6.2, 4.7, 4.7.1, 4.7.2Catalog4577015
.NET Framework 4.8Catalog4576479
Windows 10 1507
.NET Framework 3.5, 4.6, 4.6.1, 4.6.2Catalog4577049


The following table is for earlier Windows and Windows Server versions.

Product VersionSecurity and Quality RollupSecurity Only Update
Windows 8.1, Windows RT 8.1 and Windows Server 2012 R24576630
.NET Framework 3.5Catalog4569768N/AN/A
.NET Framework 4.5.2Catalog4569778N/AN/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2Catalog4576614N/AN/A
.NET Framework 4.8Catalog4576486Catalog4576489
Windows Server 20124576629
.NET Framework 3.5Catalog4569765N/AN/A
.NET Framework 4.5.2Catalog4569779N/AN/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2Catalog4576613N/AN/A
.NET Framework 4.8Catalog4576485Catalog4576488
Windows 7 SP1 and Windows Server 2008 R2 SP14576628
.NET Framework 3.5.1Catalog4569767N/AN/A
.NET Framework 4.5.2Catalog4569780N/AN/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2Catalog4576612N/AN/A
.NET Framework 4.8Catalog4576487Catalog4576490
Windows Server 20084576631
.NET Framework 2.0, 3.0Catalog4569766N/AN/A
.NET Framework 4.5.2Catalog4569780N/AN/A
.NET Framework 4.6Catalog4576612N/AN/A


Previous Monthly Rollups

The last few .NET Framework Monthly updates are listed below for your convenience:


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  • Avatar
    Ismail Demir

    Hello Tara,

    please release only two version of the NetFx Updates for Windows7 SP1.
    One for pre ESU and one for post ESU.

    Please also cumulate all the monthly NetFx Updates and mark it as replaced/superseded.

    Thank you!

    • Avatar
      Ismail Demir

      In case of KB4569767, the support page has a note that the update KB4569767 replace the update 4566517 but the catalog page doesn’t.

      See links above

      • Tara Overfield
        Tara OverfieldMicrosoft employee

        Currently, the .NET team calculates supersedence at the parent KB level – not the child KB level. If you search for the parent KB on catalog, for example KB4576628, then the supersedence is listed. We will consider also adding supersedence at the individual/child patch level.

        • Avatar
          Ismail Demir

          Hello Tara,

          note, on fresh installation of w7sp1 (net3.5) following updates appears on windows update:

          • kb4041083 (child kb4040980; dated 09/2017)
          • kb4049016 (child kb4040980; dated 11/2017)


          • kb4535102 (child kb4532945; dated 01/2020)

          -> kb4535102 replaces kb4040980, in fact kb4041083 and kb4049016!

    • Avatar
      Ismail Demir

      … to bring it up (again)

      kb2931356 with kb2836943-v2 and kb2894844 should be merged into kb4569767 (monthly)

      kb3023215 and kb2789645 should be merged into/with kb4569767 (monthly)

      kb4040980 should be merged into/with kb4569767 (monthly)

      All files are fragmented and should be merged together!

      Btw. The Windows7 monthly update (kb4577051) has not merged all files from prior monthly kb4571729! Looks like IE update reverted or not included!

  • Avatar
    Jason Baginski

    Slight oddity. Did anything change with how AppPools are handled? We had some complaints this morning about some issues with one particular site. This particular project has two AppPools, one is an admin site the other is the actual user site. The complaints were described as “going in and out” and occasional “request too large” errors. When loading up IIS to see if any configuration values had changed, we noticed that the AdminAppPool had 2 applications listed while the UserAppPool had 0. We double checked the site configuration and each site had the proper AppPool listed. The only thing slightly abnormal about these AppPools compared to the rest is the names had dashes in them(as per the company name). After renaming them to no longer have dashes, they each show the proper number of applications(1 and 1). After the rename, there also haven’t been any further issues reported. I’m mostly posting this here as a reference in case someone else is having some odd behavior after applying this update so they have one more thing to check.