added AIX reference

Author: h00die

documentation/modules/auxiliary/scanner/rservices/rsh_login.md

@@ -4,7 +4,9 @@ The R Services (rexecd, rlogind, and rshd) are a suite of unencrypted remote com
 These services are all but unused in modern computing, as they have been replace by telnet and ssh.
 
 `rsh` relies on host names as a security mechanism.  Utilizing `+` can wildcard so any computer can connect.  In the following
-config, we'll utilize that wildcarded setting to simplify our exploitation.  This is a glaring security issue!!!
+config, we'll utilize that wildcarded setting to simplify our exploitation.  **This is a glaring security issue!!!**
+However, there are exceptions to this in proprietary Unix systems which may include other mechanisms such as Kerberos
+([AIX](https://www.ibm.com/support/knowledgecenter/en/ssw_aix_71/com.ibm.aix.cmds4/rsh.htm))
 
 If you encounter `Host address mismatch for `..., you may need to adjust your `/etc/hosts` file accordingly.
 
@@ -52,4 +54,4 @@ The following was done on Kali linux:
 
 ## Confirming
 
-At the time of writing this, there was no `nmap` script equivalent.  Most modern systems have also replaced `rsh` with `ssh`.
+At the time of writing this, there was no `nmap` script equivalent.  Most modern systems have also replaced `rsh` with `ssh`.