Balanced Security for IPv6 CPE
draft-v6ops-vyncke-balanced-ipv6-security-01.txt

Abstract

This document describes how an IPv6 residential Customer Premise Equipment (CPE) can have a balanced security policy that allows for a mostly end-to-end connectivity while keeping the major threats outside of the home. It is based on an actual IPv6 deployment by Swisscom and proposes to allow all packets inbound/outbound EXCEPT for some layer-4 ports where attacks and vulnerabilities (such as weak passwords) are well-known.

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Status of This Memo

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Copyright Notice

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Threats
• 3. Overview
• 3.1. Rules for Balanced Security Policy
• 3.2. Rules example for Layer-4 Protection as Used by Swisscom
• 4. IANA Considerations
• 5. Security Considerations
• 6. Acknowledgements
• 7. Informative References
• Authors' Addresses

1. Introduction

Internet access in residential IPv4 deployments generally consist of a single IPv4 address provided by the service provider for each home. Residential CPE then translates the single address into multiple private IPv4 addresses allowing more than one device in the home, but at the cost of losing end-to-end reachability. IPv6 allows all devices to have a unique, global, IP address, restoring end-to-end reachability directly between any device. Such reachability is very powerful for ubiquitous global connectivity, and is often heralded as one of the significant advantages to IPv6 over IPv4. Despite this, concern about exposure to inbound packets from the IPv6 Internet (which would otherwise be dropped by the address translation function if they had been sent from the IPv4 Internet) remain. This document describes firewall functionality for an IPv6 CPE which departs from the "simple security" model described in [RFC6092] . The intention is to provide an example of a security model which allows most traffic, including incoming unsolicited packets and connections, to traverse the CPE unless the CPE identifies the traffic as potentially harmful based on a set of rules. This model has been deployed successfully in Switzerland by Swisscom without any known security incident.

This document is applicable to off-the-shelves CPE as well to managed Service Provider CPE or for mobile Service Providers (where it can be centrally implemented).

2. Threats

For a typical residential network connected to the Internet over a broadband connection, the threats can be classified into:

• denial of service by packet flooding: overwhelming either the access bandwidth or the bandwidth of a slower link in the residential network (like a slow home automation network) or the CPU power of a slow IPv6 host (like networked thermostat or any other sensor type nodes);
• denial of service by Neighbor Discovery cache exhaustion [RFC6583]: the outside attacker floods the inside prefix(es) with packets with a random destination address forcing the CPE to exhaust its memory and its CPU in useless Neighbor Solicitations;
• denial of service by service requests: like sending print jobs from the Internet to an ink jet printer until the ink cartridge is empty or like filing some file server with junk data;
• unauthorized use of services: like accessing a webcam or a file server which are open to anonymous access within the residential network but should not be accessed from outside of the home network or accessing to remote desktop or SSH with weak password protection;
• exploiting a vulnerability in the host in order to get access to data or to execute some arbitrary code in the attacked host such as several against old versions of Windows;
• trojanized host (belonging to a Botnet) can communicate via a covert channel to its master and launch attacks to Internet targets.

3. Overview

The basic goal is to provide a pre-defined security policy which aims to block known harmful traffic and allow the rest, restoring as much of end-to-end communication as possible. This pre-defined policy can be centrally updated and could also be a member of a security policy menu for the subscriber.

3.1. Rules for Balanced Security Policy

These are an example set of generic rules to be applied. Each would normally be configurable, either by the user directly or on behalf of the user by a subscription service.

If we name all nodes on the residential side of the CPE as 'inside' and all nodes on the Internet as 'outside', and any packet sent from outside to inside as being 'inbound' and 'outbound' in the other direction, then the behavior of the CPE is described by a small set or rules:

1. Rule RejectBogon: apply ingress filtering in both directions per [RFC3704] and [RFC2827] for example with unicast reverse path forwarding (uRPF) checks (anti-spoofing) for all inbound and outbound traffic (implicitly blocking link-local and ULA in the same shot), this is basically the Section 2.1 Basic Sanitation and Section 3.1 Stateless Filters of [RFC6092];
2. Rule ProtectWeakServices: drop all inbound and outbound packets whose layer-4 destination is part of a limited set (see Section 3.2), the intent is to protect against the most common unauthorized access and avoid propagation of worms (even if the latter is questionable in IPv6); an advanced residential user should be able to modify this pre-defined list;
3. Rule Openess: allow all unsolicited inbound packets with rate limiting the initial packet of a new connection (such as TCP SYN, SCTP INIT or DCCP-request not applicable to UDP) to provide very basic protection against SYN port and address scanning attacks. All transport protocols and all non-deprecated extension headers are accepted. This a the major deviation from REC-11, REC-17 and REC-33 of [RFC6092].
4. All requirements of [RFC6092] except REC-11, REC-18 and REC-33 must be supported.

3.2. Rules example for Layer-4 Protection as Used by Swisscom

The rule ProtectWeakService can be implemented by using the following suggestions as implemented by Swisscom in 2013: