Unknown attachment error in Confluence Server and Data Center 7.12 and earlier

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Platform Notice: Server and Data Center Only - This article only applies to Atlassian products on the server and data center platforms.


There are some situations where when you insert an image into a page, Confluence incorrectly renders the image as unknown attachment, even though the file is attached to the page.  

CONFSERVER-55928 - Unknown attachment.png

Screenshot showing unknown attachment placeholder


This problem was caused by a bug in Confluence Server and Data Center.

See CONFSERVER-55928 - Getting issue details... STATUS for more details of the issue. 


The underlying problem that causes this behaviour was fixed in Confluence 7.12.1, and backported to 7.4.9.  However this fix only prevents the problem from happening in future, it does not repair existing broken attachments.  

To help with this, we've created a small app which will attempt to reconcile unknown attachments when someone views or edits a page.  The Confluence Unknown Attachment Reconciliation Plugin can be installed on Confluence Server and Data Center 7.4.8 and later.  

To get the app:

  1. Go to https://marketplace.atlassian.com/apps/1225406/reconcile-unknown-attachments
  2. Select Get it now to download the app file. 
  3. Go to  > Manage apps.
  4. Select Upload and choose the reconcile-unknown-attachments-1.x.x.jar file you downloaded from marketplace. 

How does it work? 

When someone views a page, the app will attempt to display the unknown attachment correctly, but won't actually save the repaired content. The repaired content will be saved when someone edits the page and publishes their changes. There are some limitations to be aware of, detailed below. 

The app will:

  • Attempt to reconcile the unknown attachment placeholder with an attached file, using page metadata.
  • Attempt to reconcile the unknown attachment placeholder with an attached file, where there is only one file attached to the page. 
  • Allow people editing the page to manually repair an unknown attachment. Editors can click the unknown attachment placeholder, then choose the appropriate attached file from the Insert File dialog with a single click. 
  • Record a number of analytics events that will help us understand why the unknown attachment could or could not be reconciled. These are only sent to Atlassian if you have opted in to Atlassian Analytics. 
  • Add additional metadata to affected pages that could not be repaired, which will enable us to target these pages later as we improve this app.  

The app won't be able to repair unknown attachments if:

  • The file is missing from the file system (which is not a symptom of this bug).
  • There is not enough metadata in the storage format to match the unknown attachment to the attached file, and there is more than one file attached to the page.
  • The page has unpublished changes because when the existing shared draft is published, some of the page metadata is lost from the storage format. This can lead to a situation where a page displays correctly when viewed, but after publishing the unpublished changes, the attachments will revert to unknown attachment again. In this situation, edit the page, and click the unknown attachment placeholder to select the correct file to display. 

DescriptionUnknown attachment error in Confluence Server and Data Center 7.12 and earlier

Last modified on Oct 11, 2021

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