I had the same problem on CentOS 6.3 w/ NGINX and found the answer to be in the iptables on the vagrant box.
From bash on the vagrant box, follow these steps:
First list current iptable rules
iptables -L -v
Then flush current rules:
iptables -F
Allow SSH connections on tcp port 22
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
Set default policies for INPUT, FORWARD and OUTPUT chains
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
Set access for localhost
iptables -A INPUT -i lo -j ACCEPT
Accept packets belonging to established and related connections
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Save settings
/sbin/service iptables save
List modified rules
iptables -L -v
Curl localhost:[port#] or hit it in your browser from outside vagrant
More info on CentOS iptable configs found here:
http://wiki.centos.org/HowTos/Network/IPTables
Good luck.