Agent field is set but not run the function in shell shock

I try to solve seed lab shell shock vulnerability lab in that, i set the agent field by bellow commandCurl -A "() {echo hello;}; Content_type: text/plain; echo; /bin/ls -l " http://localhost/cgi-bin/sample.cgi

The out put is still the hello word that placed inside the cgi script

I test the agent field by checking environment variables. It was set to my command but not executed? Any suggestions for why the bash was not parse this to function