diff --git a/salt/reactor/sominion_setup.sls b/salt/reactor/sominion_setup.sls
index 64b3666f4..a72348cc8 100644
--- a/salt/reactor/sominion_setup.sls
+++ b/salt/reactor/sominion_setup.sls
@@ -6,39 +6,74 @@
 # Elastic License 2.0.
 
 import logging
-from subprocess import call
-import yaml
+import os
+import re
+import shlex
+import subprocess
 
 log = logging.getLogger(__name__)
 
+SO_MINION = '/usr/sbin/so-minion'
+
+_NODETYPE_RE = re.compile(r'^[A-Z][A-Z0-9_]{0,31}$')
+_MINIONID_RE = re.compile(r'^[A-Za-z0-9._-]{1,253}$')
+_HOSTPART_RE = re.compile(r'^[A-Za-z0-9._-]{1,253}$')
+_IPV4_RE = re.compile(
+    r'^(?:(?:25[0-5]|2[0-4]\d|[01]?\d?\d)\.){3}'
+    r'(?:25[0-5]|2[0-4]\d|[01]?\d?\d)$'
+)
+_HEAP_RE = re.compile(r'^\d{1,6}[kKmMgG]?$')
+
+
+def _check(name, value, pattern):
+  s = str(value)
+  if not pattern.match(s):
+    raise ValueError("sominion_setup_reactor: refusing unsafe %s=%r" % (name, value))
+  return s
+
+
 def run():
   log.info('sominion_setup_reactor: Running')
   minionid = data['id']
   DATA = data['data']
-  hv_name = DATA['HYPERVISOR_HOST']
   log.info('sominion_setup_reactor: DATA: %s' % DATA)
 
-  # Build the base command
-  cmd = "NODETYPE=" + DATA['NODETYPE'] + " /usr/sbin/so-minion -o=addVM -m=" + minionid + " -n=" + DATA['MNIC'] + " -i=" + DATA['MAINIP'] + " -c=" + str(DATA['CPUCORES']) + " -d='" + DATA['NODE_DESCRIPTION'] + "'"
-  
-  # Add optional arguments only if they exist in DATA
+  nodetype = _check('NODETYPE', DATA['NODETYPE'], _NODETYPE_RE)
+
+  argv = [
+    SO_MINION,
+    '-o=addVM',
+    '-m=' + _check('minionid', minionid,        _MINIONID_RE),
+    '-n=' + _check('MNIC',     DATA['MNIC'],    _HOSTPART_RE),
+    '-i=' + _check('MAINIP',   DATA['MAINIP'],  _IPV4_RE),
+    '-c=' + str(int(DATA['CPUCORES'])),
+    '-d=' + str(DATA['NODE_DESCRIPTION']),
+  ]
+
   if 'CORECOUNT' in DATA:
-    cmd += " -C=" + str(DATA['CORECOUNT'])
-    
+    argv.append('-C=' + str(int(DATA['CORECOUNT'])))
+
   if 'INTERFACE' in DATA:
-    cmd += " -a=" + DATA['INTERFACE']
-  
+    argv.append('-a=' + _check('INTERFACE', DATA['INTERFACE'], _HOSTPART_RE))
+
   if 'ES_HEAP_SIZE' in DATA:
-    cmd += " -e=" + DATA['ES_HEAP_SIZE']
-  
+    argv.append('-e=' + _check('ES_HEAP_SIZE', DATA['ES_HEAP_SIZE'], _HEAP_RE))
+
   if 'LS_HEAP_SIZE' in DATA:
-    cmd += " -l=" + DATA['LS_HEAP_SIZE']
+    argv.append('-l=' + _check('LS_HEAP_SIZE', DATA['LS_HEAP_SIZE'], _HEAP_RE))
 
   if 'LSHOSTNAME' in DATA:
-    cmd += " -L=" + DATA['LSHOSTNAME']
-  
-  log.info('sominion_setup_reactor: Command: %s' % cmd)
-  rc = call(cmd, shell=True)
+    argv.append('-L=' + _check('LSHOSTNAME', DATA['LSHOSTNAME'], _HOSTPART_RE))
+
+  env = os.environ.copy()
+  env['NODETYPE'] = nodetype
+
+  log.info(
+    'sominion_setup_reactor: argv: %s (NODETYPE=%s)',
+    ' '.join(shlex.quote(a) for a in argv),
+    shlex.quote(nodetype),
+  )
+  rc = subprocess.call(argv, shell=False, env=env)
 
   log.info('sominion_setup_reactor: rc: %s' % rc)