- From: Emil Lundberg via GitHub <sysbot+gh@w3.org>
- Date: Tue, 29 Mar 2022 17:41:55 +0000
- To: public-webauthn@w3.org
Yeah, the critical piece to realize is that all WebAuthn credentials are "trust on first use" (TOFU) keys. Even with attestation, it is indeed possible for a malicious script to replace the public key and attestation statement during registration, and thus have the attacker's key registered instead of the victim's key. We touch on this in [13.4.4. Attestation Limitations](https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-attestation-limitations) in the Security Considerations section. What attestation does is provide a way for the authenticator to prove to the RP what _kind_ of authenticator it is. That proof could eliminate the possibility of software-generated malicious keys, but a malicious script could still in theory call out a remote server to generate an attestation statement using a genuine authenticator on the RP's allow list. At best the RP could display a name and/or image of the authenticator as identified by the attestation statement, which could allow attentive users to notice if there's a discrepancy. But even then the attacker's remote server could have an array of authenticators of different brands and models to account for that too. And of course, [self attestation](https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#self-attestation) is always susceptible to tampering since by definition there's no way to link the attestation key to any established root of trust. So yeah, the registration ceremony is a [leap of faith](https://datatracker.ietf.org/doc/html/rfc4949#page-182), with or without attestation. But assuming one was completed securely, any subsequent authentication ceremonies are highly resistant to tampering since at that point there is an established trust relationship with a particular credential public key. You cannot know with certainty who the public key came from during registration, but you can know with certainty that an authentication signature came from _the same_ key pair as was registered. -- GitHub Notification of comment by emlun Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1710#issuecomment-1082187565 using your GitHub account -- Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config
Received on Tuesday, 29 March 2022 17:42:02 UTC