Steps to Reproduce:

1. Install Confluence
2. Configure Attachment Limit via Administrations > General Configurations > Attachment Settings to 30MB. i.e: 31457280 Bytes
3. Create new page in Confluence
4. (Expected) Attach a 32MB file via Page > Attachments > Upload File > Confluence will throws a message stating file is too large.
5. (BUG) Attach lot larger file like 47MB via Page > Attachments > Upload File >
   

Expected Result

Confluence will throws the message "Total upload size is too large (X MB). Reduce total filesize to below X MB"

Actual Result

• In Chrome, ERR_CONNECTION_RESET is thrown in the browser.
• In Firefox The connection was reset is thrown
• In atlassian-confluence.log, following traces can be found:

  2017-11-21 22:51:34,826 ERROR [http-nio-8621-exec-5] [com.atlassian.xwork.FileUploadUtils] checkMultiPartRequestForErrors java.io.IOException: Content Length Error (31460203 > 31457280)
   -- url: /confluence/pages/doattachfile.action | page: 4227074 | traceId: c0dcbdcaa180636c | userName: johndoe | referer: http://localhost:8621/confluence/pages/doattachfile.action?pageId=4227074 | action: doattachfile
  

Workaround

Use Drag & Drop instead of Upload File