Windows IP Security Filters October 23, 2002 Joe Klemencic Fermilab Business Services

What are IP Security Filters?  New feature in Windows 2000, XP &.NET  Initially created to authenticate and encrypt communications  Packet Filtering method adopted by Microsoft during Windows 2000 beta testing

Intended Usage  Authenticate host connections  Negotiate encryption schemes  Filter access to services by host/subnet It is important to note that the Authentication schemes are not User based authentication, but Machine based authentication.

Default Defined Policies  Client (Respond Only)  Request Security (Server)  Require Security (Server) Clients attempting to connect to resources that require Authentication and/or Encryption must have an appropriately configured response policy.

IP Security Policy Creation  Group Policy Editor (gpedit.msc) MMC Snap-In GUI manager  Group Policy Editor within an Active Directory OU Properties  IPSECPOL.EXE command line utility from the W2K Resource Kit (Windows 2000)  IPSECCMD.EXE command line utility from the Support Tools on the media CD (XP &.NET) Proper planning and testing is the key to a successful policy creation and implementation

Anatomy of an IP Security Policy  An IP Security Policy consists of: –IP Filters Define who, what, where –Source IP/Network Address –Destination IP/Network Address –Protocol/Port/Service –IP Filter Actions Define how –Permit –Block –Negotiate Security (Authenticate/Encrypt) Kerberos (Requires W2K Domain) PKI Shared Key

IP Security Filter Modes  Dynamic Mode –Adds anonymous rules to the policy agent –Can co-exist with a DS based policy  Static Mode –Creates or modifies the stored policy –Overwrites current named policy or activates new named policy

IP Filter Evaluation Order Rule Evaluation is from Most Granular to Least Specific 1. My IP Address 2. Specific IP Address Defined 3. Specific IP Subnet 4. Any IP Address A. Specific Protocol/Port combination B. Specific Protocol/Any Port C. Any Protocol

IP Filter Evaluation Order (cont) Visualize filter rule processing by applying weights Source/Destination Addresses: My IP Address: 3 Specific IP Address: 2 Specific Network: 1 Any Address: 0 Protocol Used: Specified (TCP/UDP/ICMP/RAW/…): 1 Any Protocol: 0 Source/Destination Service Ports: Specified (23/80/135/137/139/443/445…): 1 Any Port: 0

IP Filter Evaluation Order (cont) SourceSrc PortDestDest PortProtocolAction AnyAnyMyIPAnyAnyBlock 00300=300300=3 AnyAnyMyIP80TCPPermit 00311=500311= AnyMyIPAnyAnyPermit 10300=410300= AnyMyIP139TCPBlock 10311=610311=6 In this example, all traffic from the network, except TCP/139 would be allowed. Also allow TCP/80 traffic from anywhere would be allowed. All other traffic will be blocked.

Mirroring vs. Reverse Rules  The Mirror Rule option is only activated when defining Authentication or Encryption Filter Actions  When creating simple Permit/Block Packet Filters, always create the reverse rule at the same time to prevent inadvertent denial of legitimate traffic  BUT…. The reverse rule may inadvertently allow unsolicited connectivity

Reverse Rule  Consider the following: Src Src-Port Dst Dst-Port Prot Action MyIP Any Any 80 TCP Permit Any 80 MyIP Any TCP Permit Any Any MyIP Any Any Block In this ruleset, we are allowing the local machine to surf the Internet while prohibiting all other communication. An attacker could use a port-redirector and still connect to the local machine’s NetBios service as long as they source their connection from TCP/80.

Sample Implementation Scenarios Allow Web services from everywhere, but restrict FTP from only certain hosts Simple Packet Filtering Src Src-Port Dst Dst-Port Prot Action Any Any MyIP 80 TCP Permit MyIP 80 Any Any TCP Permit MyNet Any MyIP 21 TCP Permit MyNet Any MyIP 20 TCP Permit MyIP 21 MyNet Any TCP Permit MyIP 20 MyNet Any TCP Permit Any Any MyIP 21 TCP Block Any Any MyIP 20 TCP Block

Sample Implementation Scenarios Service Authentication Allow normal traffic from network, but request a Host to Kerberos authenticate from Wireless network This authentication is separate from the Application Authentication Mechanism Src Src-Port Dst Dst-Port Prot Action WLAN Any MyIP Any Any Kerberos Auth (auto-mirror)

Sample Implementation Scenarios Service Encryption Encrypt communications between servers while allowing for unencrypted traffic from workstations. Also, block communications from non-local workstations Src Src-Port Dst Dst-Port Prot Action DC1 Any MyIP Any Any Kerberos Auth & Encrypt (auto-mirror) MyIP Any DC1 Any Any Kerberos Auth & Encrypt (auto-mirror) MyNet Any MyIP Any Any Permit MyIP Any MyNet Any Any Permit Any Any MyIP Any Any Block

Usage Caveats Certain traffic is not inspected by an IP Policy - Anything with a source port of 88 (Kerberos)* - IKE - Multicast Traffic - Broadcast Traffic - RSVP/Quality of Service *This behavior may be changed by setting the following value in the Registry: HKLM\SYSTEM\CurrentControlSet\Services\IPSEC\NoDefaultExempt DWORD=1 See Microsoft Q article for more information

Usage Caveats (cont)  No logging available when using as a Packet Filter  Because of Rule Evaluation Order, an ill- defined rule may allow traffic intended to be blocked  Difficult to implement Packet Filtering on General Use Workstations, but optimal for Kiosks and Servers

Further Reading Securing W2K with IP Filters: Part 1 (Step-by-Step How-To Guide) Securing W2K with IP Filters: Part 2 (Implementing Encryption) Using IPSEC to Lock Down a Server Active Directory Replication Over Firewalls Microsoft Q Article: Domain Controller IPSEC Support How to Enable IPSEC Through a Firewall