Poweradmin is a web-based DNS administration tool for PowerDNS server. Versions prior to 4.2.4 and 4.3.3 use the attacker-controlled "HTTP_HOST" request header as the authoritative source for building callback URLs in its OIDC, SAML, and logout authentication flows without any validation. An unauthenticated attacker can poison the "redirect_uri" sent to the Identity Provider, causing the IdP to redirect the victim's authorization code to an attacker-controlled server - resulting in full account takeover with no credentials required. Versions 4.2.4 and 4.3.3 patch the issue.