diff --git a/src/main/java/cpw/mods/fml/common/launcher/FMLTweaker.java b/src/main/java/cpw/mods/fml/common/launcher/FMLTweaker.java
index 87d330b..2dadf9d 100644
--- a/src/main/java/cpw/mods/fml/common/launcher/FMLTweaker.java
+++ b/src/main/java/cpw/mods/fml/common/launcher/FMLTweaker.java
@@ -13,6 +13,7 @@
 
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.LogManager;
+import org.ultramine.server.UltramineSecurityManager;
 
 import com.google.common.base.Throwables;
 import com.google.common.collect.Lists;
@@ -32,7 +33,8 @@
 		System.setProperty("java.net.preferIPv4Stack", "true"); //Lets do this as early as possible. Vanilla does it in Main.main
 		try
 		{
-			System.setSecurityManager(new FMLSecurityManager());
+			FMLSecurityManager mgr = (FMLSecurityManager)(this instanceof FMLServerTweaker ? new UltramineSecurityManager() : new FMLSecurityManager());
+			System.setSecurityManager(mgr);
 		}
 		catch (SecurityException se)
 		{
diff --git a/src/main/java/cpw/mods/fml/relauncher/FMLSecurityManager.java b/src/main/java/cpw/mods/fml/relauncher/FMLSecurityManager.java
index 8fac41a..a6f1d20 100644
--- a/src/main/java/cpw/mods/fml/relauncher/FMLSecurityManager.java
+++ b/src/main/java/cpw/mods/fml/relauncher/FMLSecurityManager.java
@@ -10,6 +10,13 @@
  *
  */
 public class FMLSecurityManager extends SecurityManager {
+	private final boolean um;
+	
+	public FMLSecurityManager(){this(false);}
+	public FMLSecurityManager(boolean um)
+	{
+		this.um = um;
+	}
 	@Override
 	public void checkPermission(Permission perm)
 	{
@@ -17,8 +24,8 @@
 		if (permName.startsWith("exitVM"))
 		{
 			Class<?>[] classContexts = getClassContext();
-			String callingClass = classContexts.length > 3 ? classContexts[4].getName() : "none";
-			String callingParent = classContexts.length > 4 ? classContexts[5].getName() : "none";
+			String callingClass = classContexts.length > (um ? 4 : 3) ? classContexts[(um ? 5 : 4)].getName() : "none";
+			String callingParent = classContexts.length > (um ? 5 : 4) ? classContexts[(um ? 6 : 5)].getName() : "none";
 			// FML is allowed to call system exit and the Minecraft applet (from the quit button)
 			if (!(callingClass.startsWith("cpw.mods.fml.") || ( "net.minecraft.client.Minecraft".equals(callingClass) && "net.minecraft.client.Minecraft".equals(callingParent)) || ("net.minecraft.server.dedicated.DedicatedServer".equals(callingClass) && "net.minecraft.server.MinecraftServer".equals(callingParent))))
 			{
diff --git a/src/main/java/org/ultramine/server/UltramineSecurityManager.java b/src/main/java/org/ultramine/server/UltramineSecurityManager.java
new file mode 100644
index 0000000..4a2adc9
--- /dev/null
+++ b/src/main/java/org/ultramine/server/UltramineSecurityManager.java
@@ -0,0 +1,48 @@
+package org.ultramine.server;
+
+import java.io.File;
+import java.io.FilePermission;
+import java.io.IOException;
+import java.security.Permission;
+
+import cpw.mods.fml.relauncher.FMLSecurityManager;
+
+public class UltramineSecurityManager extends FMLSecurityManager
+{
+	private static final boolean PREVENT_FILESYSTEM_ACCESS = !Boolean.parseBoolean(System.getProperty("org.ultramine.security.allow_out_of_dir_access"));
+	private static final String JAVA_HOME = System.getProperty("java.home");
+	private final String dir;
+	
+	public UltramineSecurityManager()
+	{
+		super(true);
+		try
+		{
+			dir = new File(".").getCanonicalFile().getParentFile().getPath();
+		}
+		catch(IOException e)
+		{
+			throw new RuntimeException(e);
+		}
+	}
+	
+	@Override
+	public void checkPermission(Permission perm)
+	{
+		super.checkPermission(perm);
+		if(PREVENT_FILESYSTEM_ACCESS && perm instanceof FilePermission)
+		{
+			String name = perm.getName();
+			try
+			{
+				String path = new File(name).getCanonicalFile().getParentFile().getPath();
+				if(!path.startsWith(dir) && !path.startsWith("/dev") && !path.startsWith(JAVA_HOME))
+					throw new SecurityException("Illegal out-of-dir filesystem access: "+path);
+			}
+			catch(IOException e)
+			{
+				throw new RuntimeException("Failed to resolve canonical path for: "+name, e);
+			}
+		}
+	}
+}