The Tillitis TKey signer device application is an ed25519 signing tool. A vulnerability has been found that makes it possible to disclose portions of the TKey’s data in RAM over the USB interface. To exploit the vulnerability an attacker needs to use a custom client application and to touch the TKey. No secret is disclosed. All client applications integrating tkey-device-signer should upgrade to version 1.0.0 to receive a fix. No known workarounds are available.