I was wondering this too, I had a quick check on the League of Science website but it appears High Steve who provided a fix before is no longer around. I also sent a quick message to AlienX and he too unfortunately is no longer coding for tekkit.
Are there any kind developers around who would take up this little but useful project? (hopes)
Edit: Decided to have a peek in all the files myself, bare in mind i havent edited .class files before but from what i can tell, anyone with some basic knowledge of editing, decompiling and recompiling .class files could probably do this in 5 minutes.
I narrowed down the changes to the NEIServerPacketHandler.class files. The obvious changes I can see in the NEIServerPacketHandler.class (if statements added),
I should probably read some plugin tutorials but i feel by the time ive figured out how to make this seemingly simple fix a new version of tekkit will be out (not to mention im trying to admin a server).
If anyone with basic knowledge was capable of doing this, i think the changes in the fixed file ( http://forums.technicpack.net/threads/nei-server-mod-permission-check-exploit-fix.11032/ ), copied over to the updated nei files in the mods folder would do it.