Skribble AG - Authentication SMS for Advanced E-Signatures (AES) – Incident details

We were able to resolve the issue; all authentication SMS are now being sent normally again, including to non-Swiss phone numbers.

We are still in contact with our SMS provider to verify the root cause.

We can now confirm that the issue affects all non-Swiss phone numbers, not only German and French numbers as initially observed. Authentication SMS for AES currently work only with Swiss numbers.

We are in direct contact with our SMS provider to resolve the issue as quickly as possible.

We will provide another update as soon as we have more information.

We have detected new issues with sending authentication SMS to certain EU countries.

Currently, AES signatures for signers with German and French phone numbers are not functioning. At this stage, we cannot rule out that additional countries may also be affected.

We are investigating the full scope of the problem and are in contact with our SMS provider to resolve it.

More updates will follow as soon as we have additional information.

Incident Summary (31.10.2025 – 03.11.2025)
We experienced abuse of SMS resends in trial accounts, where SMS messages were sent to high-cost numbers outside the EU and CH.

After detection, the SMS gateway was temporarily deactivated while we analyzed the issue and implemented countermeasures.

Impact:

• Financial loss to Skribble only

• No customer data affected or exposed

Countermeasures:

• Trial (non-paying) accounts can no longer send SMS outside defined “safe” countries

• Paying customers remain unrestricted

We apologize for the disruption during this period. The temporary outage was necessary to ensure no security breach and to protect our customers from any negative impact.

Sincerely,
Waldemar Dick (CTO)

The issue has been resolved.

All authentication SMS are now fully operational again.

The issue has reopened.

A backlog of undelivered messages is currently affecting the delivery of new authentication SMS.

We are working on a solution and will provide an update as soon as more information is available.

The issue has been resolved.

AES signing for non-Swiss phone numbers is fully operational again.

More details will follow in a post-incident report.

We have identified the source of the issue and closed the entry point. To re-enable AES signing for non-Swiss phone numbers, we need to deploy an update, which is scheduled for tomorrow morning.

No customer data was at risk: the exploit misused our messaging system to trigger SMS messages, which led to an automated shutdown due to unusually high volume.

More updates will follow as soon as the deployment is completed.

Due to fraudulent use of our SMS authentication service, all authentication SMS to non-Swiss phone numbers are currently blocked for signing with AES. We are actively investigating the source of the abuse and working to close the exploited gap.

In the meantime, we recommend using SES or QES signature levels as alternatives.

We will provide an update as soon as we have more information.

We have identified the issue; it only affects authentication SMS sent to non-Swiss phone numbers.

Our team is working with our SMS provider to resolve the problem and restore full delivery.

We will provide an update as soon as we have more information.