Hardware security keys—such as those from Google and Yubico—are considered the most secure means to protect accounts from phishing and takeover attacks.
But a new research published on Thursday demonstrates how an adversary in possession of such a two-factor authentication (2FA) device can clone it by exploiting an electromagnetic side-channel in the chip embedded in it.
The vulnerability (tracked as CVE-2021-3011) allows the bad actor to extract the encryption key or the ECDSA private key linked to a victim’s account from a FIDO Universal 2nd Factor (U2F) device like Google Titan Key or YubiKey, thus completely undermining the 2FA protections.
“The adversary can sign in to the victim’s application account without the U2F device, and without the victim noticing,” NinjaLab researchers Victor Lomne and Thomas Roche said in a 60-page analysis.
“In other words, the adversary created a clone of the U2F device for the victim’s application account. This clone will give access to the application account as long as the legitimate user does not revoke its second factor authentication credentials.”
The whole list of products impacted by the flaw includes all versions of Google Titan Security Key (all versions), Yubico Yubikey Neo, Feitian FIDO NFC USB-A / K9, Feitian MultiPass FIDO / K13, Feitian ePass FIDO USB-C / K21, and Feitian FIDO NFC USB-C / K40.
Besides the security keys, the attack can also be carried out on NXP JavaCard chips, including NXP J3D081_M59_DF, NXP J3A081, NXP J2E081_M64, NXP J3D145_M59, NXP J3D081_M59, NXP J3E145_M64, and NXP J3E081_M64_DF, and their respective variants.
The key-recovery attack, while doubtless severe, needs to meet a number of prerequisites in order to be successful.
An actor will have first to steal the target’s login and password of an account secured by the physical key, then stealthily gain access to Titan Security Key in question, not to mention acquire expensive equipment costing north of $12,000, and have enough expertise to build custom software to extract the key linked to the account.
“It is still safer to use your Google Titan Security Key or other impacted products as a FIDO U2F two-factor authentication token to sign in to applications rather than not using one,” the researchers said.
To clone the U2F key, the researchers set about the task by tearing the device down using a hot air gun to remove the plastic casing and expose the two microcontrollers soldered in it — a secure enclave (NXP A700X chip) that’s used to perform the cryptographic operations and a general-purpose chip that acts as a router between the USB/NFC interfaces and the authentication microcontroller.
Once this is achieved, the researchers say it’s possible to glean the ECDSA encryption key via a side-channel attack by observing the electromagnetic radiations coming off the NXP chip during ECDSA signatures, the core cryptographic operation of the FIDO U2F protocol that’s performed when a U2F key is registered for the first time to work with a new account.
A side-channel attack typically works based on information gained from the implementation of a computer system, rather than exploiting a weakness in the software. Often, such attacks leverage timing information, power consumption, electromagnetic leaks, and acoustic signals as a source of data leakage.
By acquiring 6,000 such side-channel traces of the U2F authentication request commands over a six-hour period, the researchers said they were able to recover the ECDSA private key linked to a FIDO U2F account created for the experiment using an unsupervised machine learning model.
Although the security of a hardware security key isn’t diminished by the above attack due to the limitations involved, a potential exploitation in the wild is not inconceivable.
“Nevertheless, this work shows that the Google Titan Security Key (or other impacted products) would not avoid [an] unnoticed security breach by attackers willing to put enough effort into it,” the researchers concluded. “Users that face such a threat should probably switch to other FIDO U2F hardware security keys, where no vulnerability has yet been discovered.”
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