Balanced Security for IPv6 Residential CPE
draft-ietf-v6ops-balanced-ipv6-security-01

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 documenting an existing IPv6 deployment by Swisscom and allows all packets inbound/outbound EXCEPT for some layer-4 ports where attacks and vulnerabilities (such as weak passwords) are well-known. The policy is a proposed set of rules that can be used as a default setting. The set of blocked inbound and outbound ports is expected to be updated as threats come and go.

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Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on June 12, 2014.

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: Swisscom Implementation
• 4. IANA Considerations
• 5. Security Considerations
• 6. Acknowledgements
• 7. Informative References
• Authors' Addresses

1. Introduction

Internet access in residential IPv4 deployments generally consists of a single IPv4 address provided by the service provider for each home. The 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 globally unique 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 difference in residential default internet protection between IPv4 and IPv6 is a major concern to a sizable number of ISPs and the security policy described in this document addresses this concern without damaging IPv6 end-to-end connectivity.

The security model provided in this document is meant to be used as a pre-registered setting and potentially default one for IPv6 security in CPEs. The model departs from the "simple security" model described in [RFC6092] . It 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 policy has been deployed as a default setting in Switzerland by Swisscom for residential CPEs.

This document can be applicable to off-the-shelves CPE as well as 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 or mobile 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;
• 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 should be centrally updated, as threats are changing over time. It could also be a member of a list of pre-defined security policies available to an end-customer, for example together with "simple security" from [RFC6092] and a "strict security" policy denying access to all unexpected input packets.

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. This document does not address the statefulness of the filtering rules as its main objective is to present an approach where some protocols (identified by layer-4 ports) are assumed weak or malevolent and therefore are blocked while all other protocols are assumed benevolent and are permitted.

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), as described in Section 2.1 Basic Sanitation and Section 3.1 Stateless Filters of [RFC6092];
2. Rule AllowManagement: if the CPE is managed by the SP, then allow the management protocols (SSH, SNMP, syslog, TR-069, IPfix, ...) from/to the SP Network Operation Center;
3. 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; an advanced residential user should be able to modify this pre-defined list;
4. 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 is a the major deviation from REC-11, REC-17 and REC-33 of [RFC6092].
5. All requirements of [RFC6092] except REC-11, REC-18 and REC-33 must be supported.

3.2. Rules Example for Layer-4 Protection: Swisscom Implementation

As of 2013, Swisscom has implemented the rule ProtectWeakService as described below. This is meant as an example and must not be followed blindly: each implementer has specific needs and requirements. Furthermore, the example below will not be updated as time passes, whereas threats will evolve.