MW 1.23.3 PHP 5.4.32 MySQL 5.5.39 Lua 5.1.5

Yesterday on a wiki I administer, pages utilizing Lua modules began producing the following script error:

Lua error: Connot create process: proc_open (/dev/null): failt to open stream: Operation not permitted

And similarly, the system log file is full of this PHP Warning:

PHP Warning: proc_open(/dev/null): failed to open stream: Operation not permitted in .../extensions/Scribunto/engines/LuaStandalone/LuaStandaloneEngine.php on line 211

I know the permissions on /dev/null are correct. Any ideas how to fix this?

Thanks Bill