A flaw in the way URLs are escaped and encoded in the org.apache.sling.xss.impl.XSSAPIImpl#getValidHref and org.apache.sling.xss.impl.XSSFilterImpl#isValidHref allows special crafted URLs to pass as valid, although they carry XSS payloads. The affected versions are Apache Sling XSS Protection API 1.0.4 to 1.0.18, Apache Sling XSS Protection API Compat 1.1.0 and Apache Sling XSS Protection API 2.0.0.