YubiKeys Side Channel Attack

On September 4, 2024, security researchers revealed a significant vulnerability affecting YubiKey devices, one of the most widely used hardware security keys for two-factor authentication (2FA). This discovery has sent shockwaves through the cybersecurity community, given YubiKey's reputation for robust security.

The Vulnerability

The newly discovered vulnerability allows potential attackers to clone YubiKeys through a side-channel attack. This attack exploits electromagnetic emissions from the device during cryptographic operations, potentially compromising the security of millions of users and organizations worldwide.

Technical Details

The side-channel attack targets the ECDSA (Elliptic Curve Digital Signature Algorithm) implementation in YubiKeys. By analyzing the electromagnetic emissions during the signing process, attackers can potentially extract the private key, which is crucial for the device's security.

Affected Devices

The vulnerability affects a wide range of YubiKey models, including:

• YubiKey 5 Series
• YubiKey Bio Series
• YubiKey Security Key Series
• YubiKey FIPS Series

Impact and Implications

This vulnerability poses a significant threat to individuals and organizations relying on YubiKeys for secure authentication. The potential for key cloning undermines the fundamental security premise of hardware security tokens, which are designed to be resistant to duplication.

Real-world Risks

While the attack requires physical proximity and specialized equipment, it could be particularly dangerous in scenarios where an attacker has temporary access to a target's YubiKey, such as in shared office spaces or during travel.

How Does it Work

The recently discovered vulnerability in YubiKeys allows for potential cloning attacks through a side-channel exploit. Here are the key details about how this attack works:

1. The vulnerability stems from a flaw in a third-party cryptographic library from Infineon used in older YubiKey firmware versions[1][6].
2. It's a side-channel attack that exploits electromagnetic emissions from the device during cryptographic operations, specifically targeting the ECDSA (Elliptic Curve Digital Signature Algorithm) implementation[2][5].
3. The attack requires physical access to the YubiKey device[1][5][6].
4. Specialized and expensive equipment (around $11,000 worth) is needed to carry out the attack[5].
5. The process involves:
   • Disassembling the YubiKey using solvents or a hot air gun
   • Connecting the internal chip (Infineon SLE78) to the specialized equipment
   • Extracting private keys by analyzing timing information from the chip's operations[5][6]
6. The attack exploits non-constant computing time for modular inversion in the ECDSA implementation, which leaks information about the secret key[6].
7. Once the private key is extracted, an attacker could potentially create a clone of the YubiKey[1][5].
8. To actually gain access to accounts, an attacker would also need additional information like usernames, passwords, or PINs associated with the accounts[1][5][6].

It's important to note that while this vulnerability exists, executing such an attack is complex, expensive, and requires significant technical expertise. For most users, the risk remains low, but it may be more concerning for high-value targets or those dealing with sensitive information[5][6].

What steps should I take if my YubiKey has been cloned

If you suspect your YubiKey has been cloned or compromised, here are the key steps you should take:

1. Immediately revoke access for the compromised YubiKey on all associated accounts. Log into each service that uses the affected YubiKey and remove it as an authentication method.
2. Register any backup YubiKeys you have to your accounts to maintain secure access. Having spare keys registered is a best practice for situations like this.
3. If you don't have a backup key, purchase a new YubiKey from an authorized source. Avoid buying second-hand keys, as only those from official channels are covered by warranty.
4. Once you have a new or backup key, register it with all your important accounts and services.
5. Consider enabling additional security measures on your accounts, such as shorter session durations for FIDO authentication, to reduce the window of opportunity for potential attackers.
6. If your YubiKey was used for PIV or OpenPGP applications, consider switching to RSA keys instead of ECDSA for those use cases.
7. For any accounts that may have been compromised, change your passwords and review account activity for any suspicious actions.
8. If the cloning was part of a targeted attack or involved theft, consider reporting the incident to relevant authorities.

Remember, while this vulnerability is concerning, exploiting it requires physical access to the YubiKey, specialized equipment, and significant technical expertise. For most users, the risk remains relatively low. However, taking these precautionary steps will help ensure the continued security of your accounts.

How can I identify if my YubiKey has been cloned

To identify if your YubiKey may have been cloned, you can take the following steps:

1. Check your YubiKey's firmware version using the YubiKey Manager or Yubico Authenticator app. Keys with firmware versions prior to 5.7 are potentially vulnerable to cloning.
2. Review your account activity logs for any suspicious logins or authentication attempts, especially from unfamiliar locations or devices.
3. Look for any unexpected or unauthorized access to accounts protected by your YubiKey.
4. Be alert for any periods where your YubiKey was out of your possession or control, as physical access is required for cloning.
5. Consider if you may be a high-value target that would attract sophisticated attackers with the resources to attempt cloning.
6. Enable additional security measures like PINs or biometric verification on your YubiKey if available.
7. Monitor for any unusual behavior when using your YubiKey, such as unexpected authentication failures.
8. If your organization uses advanced monitoring, check for any detected anomalies in YubiKey usage patterns.

It's important to note that successfully cloning a YubiKey is extremely difficult and requires specialized equipment, expertise, and physical access to the device. For most users, the risk is very low. However, if you suspect your key may have been compromised, contact Yubico support and consider replacing the device as a precaution.

Yubico's Response

Yubico, the company behind YubiKey, has acknowledged the vulnerability and is working on a fix. They have emphasized that the attack is complex and requires specialized knowledge and equipment, which may limit its widespread exploitation.

Mitigation Strategies

While Yubico develops a permanent solution, they recommend users take the following precautions:

1. Keep YubiKeys physically secure at all times
2. Be vigilant of any unusual activity on accounts protected by YubiKeys
3. Consider using additional authentication methods for highly sensitive accounts

Industry Reaction

The cybersecurity community is closely monitoring this development, as it challenges the perceived invulnerability of hardware security keys. This discovery may lead to increased scrutiny of other hardware-based security solutions and potentially accelerate the development of more robust authentication technologies.

Future Implications

This vulnerability highlights the ongoing cat-and-mouse game between security providers and potential attackers. It underscores the importance of continuous security research and the need for rapid response to emerging threats in the cybersecurity landscape.

As the situation develops, users and organizations relying on YubiKeys should stay informed about updates from Yubico and consider implementing additional security measures to protect their sensitive information and accounts.