It appears it is possible to crash the IBM DataPower XS40 Security Gateway device by sending a simple (random?) string to it, over an established SSL-connection. The device reboots as a response to the input.
Tested vulnerable firmware is 220.127.116.11
Issue fixed as tested in 18.104.22.168
Tested as follows (entered attack-string is =B4abc=B4 in this case):
openssl s_client -connect [IP]:[port]
Loading 'screen' into random state - done
After this, the device crashes and reboots