Summary:
Early this week, we identified an issue with Templafy VSTO Add-ins in Microsoft Office for PC. A subset of users received a “Publisher cannot be verified” notification when starting Office desktop applications that had Templafy VSTO Add-ins installed. Our service was not down, and users who chose to install the Office Add-in from the unknown publisher could continue using our product via Office desktop. As an immediate response, we assembled a team from Engineering, Product, Support, and InfoSec to scope and address the issue. Templafy identified that the issue was only impacting customers using a particular subset of VSTO add-ins and versions. Subsequently, on Tuesday, Templafy implemented and then deployed a fix for the impacted customers, without requiring any further action from the clients, to ensure that the issue was resolved.
Issue overview:
On Sunday, 30th of April, we received support tickets indicating users were being prompted with a Microsoft Office Customization Installer notification, stating “Publisher cannot be verified.” Upon investigation, we determined that the issue was limited to Windows users who opened Microsoft Word, PowerPoint, Excel, or Outlook using Templafy One and Hive with the following VSTO Add-ins and their versions:
Templafy Web Add-ins (For MS Office on-prem, Online & Mac) were not impacted. Customers on the latest stable version of Templafy Hive were also not impacted.
Root cause:
Upon thorough investigation, we determined that the root cause was that the signing certificate, used to sign the VSTO Add-ins, could not be verified by Microsoft Office anymore due to a change in the Time Stamp Authority requirements.
The signing certificate we used was valid until the 28th of April. To ensure that Add-ins are valid after the certificate expires, we use a Time Stamp Authority (TSA) when signing add-ins. As long as the Time Stamp Authority is trusted, add-ins remain valid after the certificate expires. To enhance global security, on the 1st of June 2021, the CA/B Forum increased the required key length for Time Stamp Authority certificates to a minimum of 3072..) The Time Stamp Authority (TSA) we used when signing our add-ins was using a key length of 2048. Therefore, it was no longer trusted, resulting in the add-ins becoming invalid after the certificate expiration date.
We had anticipated this problem and had switched to a new Time Stamp Authority (TSA) when signing executable files in March 2021, but we had not correctly switched to the new TSA when signing manifest files. Because of this, after the certificate expiration date on the 28th of April, users with impacted VSTO Add-in versions who opened an Office application received the "Publisher cannot be verified" notification.
Resolution:
To resolve the issue, we manually re-signed Library, Email Signature, and Productivity VSTO Add-ins using a new certificate with a valid Time Stamp Authority without changing any behavior of the software. We manually validated the re-signed VSTO Add-ins with both Templafy One and Hive customers.
After confirmation, we re-signed all affected add-ins and programmatically updated Templafy Desktop packages for all affected Templafy One customers. Similarly, we programmatically updated all affected Hive customers to the re-signed add-ins. This process was completed by the end of Tuesday, 2nd of May. The packages with the re-signed VSTO Add-ins were automatically installed by Templafy Desktop on end users' PCs after midnight Tuesday (local time).
Going forward, we will take extra precautions to ensure that our signed packages remain valid and adhere to the necessary key length standards in order to prevent similar problems in the future.
Timeline:
Lastly, we would like to thank you for your patience and understanding during this incident. We know that disruptions to your business operations are costly and frustrating, and as outlined above, we are committed to doing everything in our power to prevent similar incidents from occurring in the future. If you have any further questions or concerns, please do not hesitate to reach out to support@templafy.com. We are always here to assist you and help you get the most out of our product. We value your business and appreciate your ongoing trust in our service.