Vikunja is an open-source self-hosted task management platform. In versions 1.0.0 through 2.3.0, when an administrator enables the per-provi

Vikunja is an open-source self-hosted task management platform. In versions 1.0.0 through 2.3.0, when an administrator enables the per-provider emailfallback option on an OpenID Connect provider, Vikunja links an SSO login to a pre-existing local (username+password) account using only the email claim from the IdP. The fallback never checks an email_verified (or Microsoft xms_edov) signal and never requires the matched account's password. An attacker who can obtain a token from the configured issuer carrying a victim's email logs in as that victim with a full session, with no consent or interaction from the victim. Version 2.4.0 fixes the issue.