Guest users were unable to access SharePoint Online sites connected to Microsoft Teams

A post-incident report has been published.

A post-incident report has been published.

Title: Guest users were unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users were unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users were redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins could have manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Final status: We've completed a period of monitoring service telemetry, and we've observed the restoration of service availability to normal levels. Additionally, during this time, we've received multiple reports from previously affected customers that they're experiencing relief from impact, and as such, we've determined this incident is resolved. Scope of impact: This issue could have impacted any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. Start time: Thursday, August 20, 2026, at 7:30 AM UTC End time: Tuesday, August 25, 2026, at 12:47 PM UTC Root cause: A change was made to significantly reduce request latency across almost all SPO requests by optimizing how the Dynamic Claims system retrieves and caches information through asynchronous tasks. There was a latent bug within the initial Dynamic Claims flow where the service checks if the organization allows guest users for M365 group memberships. The pre-check did not force App-only credential requests to MS Graph and instead relied on the absence of user context in the thread to make the call app-only. This worked previously because the user context was not correctly propagated. However, in the new asynchronous tasks, the user context was correctly propagated, and this resulted in the failure to obtain the relevant token due to the service classifying the request as App+user. In this scenario, the service logic failed silently and put an empty value (i.e. the user is not a member of any M365 group) into the Dynamic Claims cache. This resulted in Dynamic Claims refresh call to fail for guest users and then being rejected from accessing the resources. The issue was not detected by our monitoring systems in our early deployment rings (Microsoft’s internal organization etc.), as traffic for guest users is a small fraction of the overall dynamic traffic in these environments and therefore monitoring alerting thresholds were not met. Next steps: - For a more comprehensive list of next steps and actions, please refer to the Post Incident Report document. We'll provide a preliminary Post-Incident Report within two business days and a final Post-Incident Report within five business days.

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We're continuing to engage in extended monitoring while we work with reporting organizations to confirm that the issue is fully resolved. If your organization has reported this problem, we request that you follow-up with the support case owner so we can confirm that the impact has been remediated. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. Start time: Thursday, August 20, 2026, at 7:30 AM UTC Root cause: A recently deployed change interacted with dynamic claims process, causing impact. Next update by: Wednesday, August 26, 2026, at 9:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We've received some feedback indicating the impact is now resolved after we reverted the change. We're conducting persistent monitoring of the affected environment to ensure customers who previously reported the issue are seeing withstanding recovery. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. Start time: Thursday, August 20, 2026, at 7:30 AM UTC Root cause: A recently deployed change interacted with dynamic claims process, causing impact. Next update by: Wednesday, August 26, 2026, at 7:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We're continuing to contact organizations who previously reported the issue, to confirm that the impact has been resolved after reverting the change. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. Start time: Thursday, August 20, 2026, at 7:30 AM UTC Next update by: Wednesday, August 26, 2026, at 3:00 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We've identified a recently deployed change which interacted with dynamic claims process and out of an abundance of caution, we've reverted this change. We're contacting impacted organizations to confirm that this rollback has resolved the issue. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 2:30 PM UTC

We're reviewing forward synchronization protocols and other internal services to understand why the dynamic permission claims for guest users are not replicating as expected. Next update by: Tuesday, August 25, 2026, at 1:00 PM UTC This quick update is designed to give the latest information on this issue.

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We're continuing our analysis of the network trace logs to help isolate why permissions that should grant access are not being correctly applied or recognized. This analysis will help us identify the underlying cause of the access issues and determine the appropriate remediation steps. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 1:00 PM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. As a potential workaround, admins can manually add affected guest users directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Current status: We're continuing to analyze the collected network traces to determine why permissions that should grant access aren't being correctly applied or recognized. Additionally, we've identified a potential workaround that has been successful for a subset of impacted users, where affected guest users are manually added directly to the SharePoint Members group instead of relying on Microsoft 365 Group membership propagation. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 11:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: Specifically, guest users are redirected to an AccessDenied.aspx page when attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. Current status: We've analyzed the collected network traces and determined that some guest users are being treated as though they don't have the permissions required to access impacted SharePoint sites, resulting in Access Denied responses. We're continuing to investigate why permissions that should grant access aren't being correctly applied or recognized. We're reaching out to a subset of affected users to collect additional traces that capture the process of adding guest users and assigning permissions to further our investigation. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 9:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: The issue is specifically happening when permissions to the SharePoint Online sites are granted through Microsoft 365 groups. Current status: We've collected additional network traces and are investigating why the guest users are seeing access denied errors. We suspect that there's an issue happening with permissions, and we're analyzing logs to confirm any potential issue that could be causing the impact. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 8:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: The issue is specifically happening when permissions to the SharePoint Online sites are granted through Microsoft 365 groups. Current status: We're working to collect additional network traces from affected users for analysis. In addition, we're reviewing whether any recent service changes could be contributing to the impact. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 6:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: The issue is specifically happening when permissions to the SharePoint Online sites are granted through Microsoft 365 groups. Current status: We're analyzing system logs to better understand the behavior with the guest users, which will help us to determine our next troubleshoot steps. Scope of impact: This issue could impact any guest users attempting to access SharePoint Online sites where access is granted through Microsoft 365 Groups. This information may be updated as our investigation continues. Next update by: Tuesday, August 25, 2026, at 4:30 AM UTC

Title: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams User impact: Guest users are unable to access SharePoint Online sites connected to Microsoft Teams. More info: The issue is specifically happening when permissions to the SharePoint Online sites are granted through Microsoft 365 groups. Current status: We're investigating a potential issue with SharePoint Online and checking for impact to your organization. We'll provide an update within 30 minutes.