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 188.8.131.52
Issue fixed as tested in 184.108.40.206
Tested as follows (entered attack-string is abc in this case):
openssl s_client -connect [IP]:[port]
Loading 'screen' into random state - done
After this, the device crashes and reboots