It's possible to build recursive template, leading to memory exhaustion.
vulners.com/securityvulns/securityvulns:doc:26278
vulners.com/securityvulns/securityvulns:doc:26380
vulners.com/securityvulns/securityvulns:doc:29030
vulners.com/securityvulns/securityvulns:doc:29087
vulners.com/securityvulns/securityvulns:doc:29251