The SlingRequestDispatcher doesn't correctly implement the RequestDispatcher API resulting in a generic type of include-based cross-site scripting issues on the Apache Sling level. The vulnerability is exploitable by an attacker that is able to include a resource with specific content-type and control the include path (i.e. writing content). The impact of a successful attack is privilege escalation to administrative power.
Please update to Apache Sling Engine >= 2.14.0 and enable the "Check Content-Type overrides" configuration option.