A remote code execution vulnerability occurs in OpenTSDB through 2.4.0 via command injection in the yrange parameter. The yrange value is written to a gnuplot file in the /tmp directory. This file is then executed via the mygnuplot.sh shell script. (tsd/GraphHandler.java attempted to prevent command injections by blocking backticks but this is insufficient.)
https://github.com/OpenTSDB/opentsdb/issues/2051
http://packetstormsecurity.com/files/170331/OpenTSDB-2.4.0-Command-Injection.html