An issue was discovered in the oidc (aka OpenID Connect Authentication) extension before 4.0.0 for TYPO3. The account linking logic allows a pre-hijacking attack, leading to Account Takeover. The attack can only be exploited if the following requirements are met: (1) an attacker can anticipate the e-mail address of the user, (2) an attacker can register a public frontend user account using that e-mail address before the user's first OIDC login, and (3) the IDP returns an email field containing the e-mail address of the user,
The authentication service of the extension does not verify the OpenID Connect authentication state from the user lookup chain. Instead, the authentication service authenticates every valid frontend user from the user lookup chain, where the frontend user field “tx_oidc” is not empty.
In scenarios, where either ext:felogin is active or where `$GLOBALS['TYPO3_CONF_VARS'][‘FE’][‘checkFeUserPid’]` is disabled, an attacker can login to OpenID Connect frontend user accounts by providing a valid username and any password.