We found a vulnerability in a threshold signature scheme that allows an attacker to recover the signing key of threshold ECDSA implementations that are based on Oblivious Transfer (OT). The extended OT sender cannot cheat, but the protocol is not secure against a cheating extended OT receiver. Recall that in the context of threshold signature schemes based on OT, you want to perform the base OTs once during a set-up phase and reuse this set-up arbitrarily many times to perform OT extension.