A reflected cross-site scripting vulnerability in the popup invocation options of Revive Adserver 6.0.8 and earlier allows an unauthenticated attacker to execute JavaScript in an authenticated user's browser by persuading them to visit a crafted URL. The top, left, timeout and delay request parameters are included in HTML attributes without appropriate encoding. Exploitation requires an existing popup zone, which can be created through the administrator API but is not offered by the normal zone-creation interface. The issue is fixed in Revive Adserver 6.0.9 by HTML-encoding the affected popup option values.