Microsoft Office version 2609 & CDM breaking change

Update timeline

1. identified Sep 23, 2026, 01:03 PM UTC

   Microsoft Office & CDM breaking change: We are aware that the latest version of MS Office, released 22nd September contains a breaking change to CDM which could cause work to be lost. Source: Version 2609 , build 20430.20092 was released 22nd September 2026 via Current Channel updates and contains a version of MS Word which does not allow files to be saved correctly through Cloud Drive Mapper. Behaviour: The following workflows are potentially impacted: • Opening a Word document from a mapped drive and using Save As • Creating a document locally and saving it to a mapped drive • Using Save a Copy to a mapped drive Recommendation: Customers who have not yet updated Microsoft Office to Version 2609 (Build 20430.20092) should prevent or defer deployment of this Office build to devices using Cloud Drive Mapper. Customers who have already updated to the affected Office build should roll Microsoft 365 Apps back to the previous build (Version 2608 (Build 20326.20158)) and prevent Office from automatically updating to Version 2609 while the issue is being investigated. Fix: We have raised a Bug which our development teams are working on as a priority. We will provide an update once investigations have concluded as to how we will address the issue. Microsoft release notes for Office are here: https://learn.microsoft.com/en-us/officeupdates/current-channel

2. resolved Sep 26, 2026, 02:01 PM UTC

   Work over the weekend has identified that the issue has been resolved without intervention to CDM. No update to MS Office or changes to CDM are required. We believe a follow up backend fix from Microsoft has caused this behaviour. The incident is therefore considered closed; we will continue to monitor fix stability next week.

3. postmortem Sep 28, 2026, 07:26 AM UTC

   MS have confirmed the breaking change and the issue of a fix over the weekend. Microsoft admins can review the service status notification from MS here: [https://admin.cloud.microsoft/?#/servicehealth/:/alerts/OP1478558](https://admin.cloud.microsoft/?#/servicehealth/:/alerts/OP1478558) The text from this Microsoft advisory follows: Users may be unable to convert Microsoft Word desktop app documents to PDFs using Save As to SharePoint locations Issue ID: OP1478558 Affected services: Microsoft 365 apps Status: Service degradation Issue type: Advisory Start time: Sep 24, 2026, 7:23 PM GMT\+1 More info This issue is reported to affect Microsoft Word version 2609, and some users report that version 2608 isn't affected. No error is presented and the file is instead saved to the “C:\\Users\\username\\AppData\\Local\\Microsoft\\Windows\\INetCache\\Content.MSO” folder with an incorrect file name. Additionally, this only reported to only impact converting Microsoft Word desktop app documents to PDFs using Save As and SharePoint Online as the location. While we're focused on remediation, users that have the option to save the file locally to their computer may use this to work around the problem. Additionally, using the Export to PDF function works as expected. Scope of impact This event may impact any user on version 2609 attempting to save Microsoft Word desktop app documents as PDFs to SharePoint Online. This information may be updated as our investigation continues. Root cause A recent Microsoft Word change relating to the Save As filename validation path to cloud-backed locations, which prevents the SharePoint save flow from completing and is causing impact. Current status Sep 25, 2026, 8:28 PM GMT\+1 We've confirmed that the issue is related to a recent Microsoft Word change affecting Save As filename validation for cloud-backed locations. This validation issue prevents the SharePoint save process from completing successfully during PDF conversion. We're actively deploying a change to disable the impacting behavior and expect this deployment to be completed by our next scheduled update. Next update by: Monday, September 28, 2026 at 10:00 PM GMT\+1