KB4577586 is Microsoft’s October 27, 2020 update for removing the Adobe Flash Player component installed by certain Windows versions. It is not documented as a universal tool that blocks every Flash copy or browser route: Microsoft says it removes the Flash installation supplied by the applicable Windows version, while a Flash Player installed manually from another source is outside that scope.
What KB4577586 is
Microsoft Support describes KB4577586 as the “Update for the removal of Adobe Flash Player,” published October 27, 2020. The update was part of Microsoft’s response to Adobe Flash Player reaching its support end date on December 31, 2020. The official article is available at Microsoft Support’s KB4577586 documentation.
The important distinction is what Microsoft means by removal. KB4577586 removes the Flash Player installed by the listed Windows release. Microsoft separately states that it does not remove a Flash Player manually installed from another source. Therefore, describing it as a general-purpose block on every Flash installation would be broader than the documented behavior.
Which Windows versions Microsoft listed
Microsoft’s article gives the following historical “Applies to” list. It describes the versions covered by that 2020 servicing document, not the current support status of those operating systems.
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| Product | Versions listed by Microsoft |
|---|---|
| Windows 10 | 1909, 1903, 1809, 1803, 1709, 1703 and 1607 |
| Windows Server | Windows Server 2019, 2016, 1809, 1803 and 1709 |
| Windows Server 2012 family | Windows Server 2012 and Windows Server 2012 R2 |
| Windows 8.1 family | Windows 8.1 and Windows RT 8.1 |
What the update removes—and what it does not
Windows-installed Flash
The update targets the Adobe Flash Player integrated or installed by the applicable Windows version. Once that component is removed, applications that depended on that Windows-provided Flash installation cannot rely on it being present.
Manually installed Flash
A Flash Player installed manually from another source is not removed according to Microsoft’s scope note. That qualification matters on machines where an administrator or user installed a separate third-party package.
Third-party registry settings
Microsoft lists a known issue: applying KB4577586 may remove registry settings for a third-party Flash Player version. The documented resolution is to reinstall that third-party version. This does not change Microsoft’s statement that the update itself does not remove manually installed Flash binaries in general.
How KB4577586 was delivered
Microsoft identified the update as optional in Windows Update and Windows Server Update Services (WSUS). Administrators who needed the standalone package were directed to the Microsoft Update Catalog.
| Route | Microsoft’s description | Practical implication |
|---|---|---|
| Windows Update | Optional update | It was not presented as a mandatory automatic installation in the support article. |
| WSUS | Optional update | Organizations could evaluate and approve it through their servicing workflow. |
| Microsoft Update Catalog | Standalone package available | Administrators could obtain the package directly for supported deployment scenarios. |
Can KB4577586 be uninstalled?
No. Microsoft Support states: “After this update has been applied, this update cannot be uninstalled.” Treat that as a deployment decision, especially on systems that still have a legacy Flash-dependent application.
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Normal Windows Update removal controls should not be expected to roll back this package. Check application compatibility before approving it rather than assuming it can be removed later.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to use Flash again after applying it
Microsoft lists two recovery approaches, neither of which is a routine uninstall:
- Restore to an earlier system restore point. This is possible only if System Protection had been explicitly enabled and a restore point was created before KB4577586 was applied. If no qualifying restore point exists, this route is unavailable.
- Reinstall Windows without applying the update. Microsoft describes reinstalling the operating system and omitting KB4577586 as the other method for restoring the prior state.
These are system-level recovery procedures, not guaranteed, low-risk workarounds. Preserve required data and verify that the chosen recovery method is appropriate for the device before proceeding.
Checks to make before deployment
- Identify whether the workload uses the Flash Player supplied by Windows or a separately installed package.
- Record the Windows edition and version against Microsoft’s historical applicability list.
- Check whether System Protection is enabled and whether a pre-update restore point exists if rollback might be required.
- Test any legacy line-of-business application that may still depend on Flash.
- For third-party Flash installations, document the package and its registry configuration so it can be reinstalled if the known issue occurs.
Bottom line on the “block Flash” wording
KB4577586 is best understood as Microsoft’s Windows-installed Flash removal update, dated October 27, 2020. It removes the Flash component provided by the covered Windows release, was offered as an optional update through Windows Update and WSUS with a Catalog package, and cannot be uninstalled after application. It does not, according to Microsoft’s documentation, remove every manually installed Flash copy or establish a universal block on all Flash delivery mechanisms.
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