The Goobi viewer is a web application that allows digitised material to be displayed in a web browser. Prior to version 26.05, the legacy RSS servlet (RssResolver, GET /rss/) accepts the q and filterQuery parameters and concatenates them into Solr queries without validation. The servlet predates the REST API layer and lacks the input validation present in GET /api/v1/records/rss. q forms the main query body (wrapped only in literal parentheses); filterQuery is passed directly as a Solr fq. An unauthenticated attacker can inject Solr boolean operators to break out of the wrapping and render the trailing access-condition filter-query suffix optional, so that access-restricted records are included in the generated RSS feed. The q and filterQuery parameters are the same underlying vulnerability in the same servlet; q (the main query body) has the broader scope. This issue has been patched in version 26.05.