April 2020 CU for Office Online Server is available for download

The product group released the April 2020 Cumulative Update for Office Online Server.

The KB article for April 2020 CU will be available at the following Location in a couple of hours:

  • KB 4484290 – April 2020 Update for Office Online Server – This is also a security update!

The download for April 2020 CU is available through the following link:

Related Links:


  1. Hi Stefan,

    Is there a known issue with editing word documents in Internet Explorer after the April 2020 update? Were seeing word display a quick error (Sorry, we ran into a problem Session ID: XXXXX) that disappears quickly after editing the document in IE. All other browsers are fine.

    SCRIPT5007: Object expected
    WordEditor.js (533,383)
    Time stamps on the server for the file seem to align with the list of files that are included in security update 4484290.

    Sounds like it could be related to the following improvement:
    • Improves the file lock management in Word for the web. The file lock is now released more reliably and taken for shorter durations. If the header says Saved when you leave the document, the final save will be faster



    1. Hi Jeff,

      I haven’t seen this issue and would recommend to open a ticket with Microsoft Support to get this analyzed.



    2. This issue is also happening for me. I immediately noticed it upon doing first smoke test after updating. It’s also happening for June 2020 CU so it’s not yet fixed 🙁


      1. The engineer on our case said the fix will be included in the July 2020 update to OOS


  2. Thanks Stefan. We ended up opening a sev c case. It sounds like its a known issue and the product team is currently working on a fix.


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