🚨 Security Alert: New vulnerability discovered in Yubikeys. Cloning attacks possible through side-channel exploit!
Researchers have discovered a side-channel vulnerability in the YubiKey 5 series, the most widely used hardware token for two-factor authentication based on the FIDO standard. The flaw, which resides in a microcontroller used in other authentication devices, allows attackers to clone the device when they gain temporary physical access to it. YubiKey-maker Yubico has issued an advisory, confirming that all YubiKeys running firmware prior to version 5.7 are permanently vulnerable and cannot be patched.
Vulnerability Details
The side channel is in the Infineon cryptolibrary’s implementation of the Extended Euclidean Algorithm, which performs modular inversion operations involving the Elliptic Curve Digital Signature Algorithm (ECDSA). This implementation fails to implement a common side-channel defense, constant time, resulting in execution time differences that reveal the token’s ephemeral ECDSA key. By measuring electromagnetic radiation with an oscilloscope, attackers can extract the secret ECDSA key, compromising the entire security of the token.
Attack Method
The cloning attack requires physical access to the YubiKey, knowledge of the targeted accounts, and specialized equipment. The attacker must also obtain the user’s login credentials. The process involves stealing the login and password, gaining access to the device, sending authentication requests while measuring the side-channel emissions, and then performing the attack to extract the ECDSA private key. The attacker can then create a clone of the FIDO device for the victim’s account.
Affected Devices
All YubiKey 5 series models are vulnerable, and the researchers suspect other devices using the Infineon SLE78, Infineon Optiga Trust M, and Infineon Optiga TPM microcontrollers may also be affected. Yubico has not confirmed this, and Infineon has not issued an advisory.
Recommendations
Yubico advises users to use additional security measures such as PIN codes, fingerprint or face scans, and to be cautious of physical access to their YubiKeys. Users can check their firmware version using the Yubico Authenticator app. The vulnerability does not affect two-factor authentication or one-time password
functionalities.
About the Researchers
NinjaLab co-founder Thomas Roche explained that the vulnerability exists in the Infineon cryptographic library, which is used in many security devices. The library’s implementation of the ECDSA ephemeral key modular inversion is not constant time, allowing side-channel analysis to extract the secret key. The attack requires $11,000 worth of equipment and sophisticated knowledge of electrical and cryptographic engineering.
[1] “YubiKeys are vulnerable to cloning attacks thanks to newly discovered side channel,” Ars Technica, September 3, 2024
