A newly discovered side-channel vulnerability, named 'EUCLEAK,' has been found to affect YubiKey 5 Series devices running firmware versions prior to 5.7. This vulnerability, which targets the Infineon cryptographic library, allows attackers to clone authentication devices such as YubiKeys by extracting private keys. The attack requires physical access to the device and approximately $11,000 worth of equipment. Researchers have detailed that the flaw resides in the implementation of the Extended Euclidean Algorithm. The issue is considered unfixable and affects other devices using Infineon microcontrollers, including Trezor wallets. The vulnerability, identified as YSA-2024-03, allows bypassing crucial attestation protocols and poses a significant security risk, even with just minutes of physical access.