Security researchers have discovered three new attack techniques that allow malware to exploit passkeys synchronized via Google Password Manager. The attacks do not target the cryptography behind passkeys, but rather the way Chrome and Google’s cloud infrastructure handle device trust and user authentication.
The three techniques, collectively called “Pass-ta-key,” were developed by Unit 42, the security team at Palo Alto Networks, according to BleepingComputer. They do require that an attacker has already installed malware on a Windows PC. According to the researchers, the attacks demonstrate that while passkeys help combat phishing, they offer no protection against a system that has already been compromised.
Three attack methods
The first technique allows malware to impersonate a trusted device. Using Chrome’s TPM (Trusted Platform Module) identity key, a request is signed that Google’s cloud authenticator accepts as legitimate. This enables the malware to successfully log in to some websites.
This only works if a service does not sufficiently verify user authentication. GitHub correctly blocked the attack, but eBay initially failed to properly validate this check. After being notified by the researchers, eBay fixed this issue.
The second technique, Silver Pass-ta-key, forces Chrome to re-register a device. In doing so, an attacker can link their own authentication key to the Google account. Google’s cloud authenticator then trusts this key as if it originated from the original hardware, allowing even stricter controls to be bypassed.
Stealing the master key
The third attack, Golden Pass-ta-key, is the most far-reaching. It involves stealing the Security Domain Secret (SDS), the master key used to encrypt all passkeys synchronized via Google Password Manager.
Google removed this key from Chrome’s log files after being notified. However, according to Unit 42, the SDS remains temporarily available in the browser’s working memory during registration and recovery processes. Malware can extract the key from there, decrypt all synchronized passkeys, and copy the private keys to another system.
According to the researchers, the master key also cannot be replaced or revoked, meaning that future synchronized passkeys will continue to be secured with the same key.
Passkeys remain safer
Despite the new attack techniques, Unit 42 states that passkeys remain significantly more secure than traditional passwords. After all, the attacks require that a system be already infected with malware.
The researchers advise website administrators to strictly monitor user authentication and to better secure credential managers during registration and recovery processes. Additionally, sensitive master keys should not be temporarily accessible from the browser’s memory.
Google has been made aware of the findings. At the time of publication, the company had not yet responded to BleepingComputer’s inquiry as to whether all the described vulnerabilities have now been fully addressed.