IPv6 Security 

IPv6 security is an essential component of modern network architecture. By utilizing the latest security technology, organizations can ensure their networks are secure from malicious actors and threats. IPv6 is an upgrade from the IPv4 protocol and has many advantages. It is faster, has a larger address space, and has more efficient routing protocols. It also provides better options for network segmentation, making it easier to create secure networks.

So, what is IPv6 Host Exposure? Firstly, IPv6 as a protocol suite isn’t inherently more or less secure than its predecessor. However, as with IPv4, most IPv6 attacks and security incidents arise from design and implementation issues rather than weaknesses in the underlying technology. Therefore, we need to consider critical areas of IPv6 security, such as IPv6 host exposure and the numerous IPv6 security vulnerabilities that IPv6 stacks are susceptible to.

Many organizations already have IPv6 running on their networks and must realize it. In addition, many computer operating systems now default to running both IPv4 and IPv6. This is known as dual-stack mode, which could cause security vulnerabilities if one is less secure than the other. IPv6 security vulnerabilities currently exist, and as the popularity of the IPv6 protocol increases, so does the number of IPv6 security vulnerabilities and threats.

IPv6 FHS (First Hop Security) protects IPv6 on L2 links.

Initially, you might think the first hop is the first router, but that is false. These are all features of switches, specifically those that sit between your end devices and your first router.

First Hop Security features are listed below.

• RA Guard: With RA Guard, hosts don’t care where router advertisements come from; any device on the network can transmit them. Any offer will be gladly accepted. You can filter router advertisements with RA Guard. If you inspect RAs and permit them only when they meet specific criteria, you can create a simple policy that only accepts RAs on specific interfaces.

• IPv6 DHCP Guard: similar to IPv4 DHCP snooping. Only trusted interfaces are allowed to transmit DHCP packets. Additionally, you can create policies that only allow specific prefixes and preferences to receive DHCP packets.

• Inspection of NS (Neighbor Solicitation) and NA (Neighbor Advertisement) messages: the switch inspects and stores NS and NA messages in the IPv6 binding table. If any NS/NA messages are spoofed, the switch can drop them.

• Source Gaurd: When a packet’s source address does not appear in the IPv6 binding table, the switch filters it, preventing spoofing attacks.

Guide: IPv6 security with access lists

Access lists in IPv6 are used more and less like they are in IPv4. Access lists are used to filter and select traffic. If you recall, IPv6 access lists have three invisible statements at the bottom:

1. permit icmp any any nd-na
2. permit icmp any any nd-ns
3. deny ipv6 any any

In the following screenshot, I have IPv6 access set inbound on R1 to explicitly permit telnet traffic from R2. The access list, known as an access filter, will block any other type of traffic, such as ping. As a security best practice, I recommend you also turn on “no IPv6 unreachables” on the interface. This will stop the AAAA from appearing, which is a security threat.

You don’t want a bad actor to know that an access filter is dropping their packets, as they will try to circumvent it. With the following command enabled under the interface, packets are dropped silently.

**Implications of IPv6 Host Exposure**

1. Increased attack surface: IPv6’s larger address space makes it easier for attackers to scan and identify vulnerable devices. With direct access to each device, attackers can exploit security vulnerabilities, potentially leading to unauthorized access, data breaches, or service disruptions.

2. Lack of visibility: Traditional security tools and monitoring systems primarily designed for IPv4 networks may struggle to detect and defend against threats in an IPv6 environment effectively. This lack of visibility can leave organizations unaware of potential security breaches or ongoing attacks.

3. Misconfiguration risks: IPv6 addressing and configuration complexity can result in misconfigurations, inadvertently exposing hosts to the Internet. These misconfigurations can open up opportunities for attackers to exploit and compromise devices or networks.

4. Privacy concerns: IPv6 addresses can contain unique identifiers, potentially compromising users’ privacy. This can enable tracking and profiling of individuals, raising privacy concerns for individuals and organizations.

**Challenges with IPv4 designs**

In IPv4’s initial design, network security was a minor concern. However, as IPv4 was developed and the Internet explosion occurred in the 1990s, Internet threats became prolific, and we were essentially wide open to attack. If the current circumstances of Internet threats could have been predicted when IPv4 was being developed, the protocol would have had more security measures incorporated.

IP Next Generation (IPng) was created, becoming IPv6 (RFC 1883). IPv6 is the second network layer standard protocol that follows IPv4, offers several compelling functions, and is the next step in the evolution of the Internet Protocol.

IPv6 provides several improvements over its predecessor. The following list summarizes the characteristics of IPv6 and the improvements it can deliver:

1. Larger address space: Increased address size from 32 bits to 128 bits
2. Streamlined protocol header: Improves packet-forwarding efficiency
3. Stateless autoconfiguration: The ability for nodes to determine their address
4. Multicast: Increased use of efficient one-to-many communications
5. Jumbograms: The ability to have huge packet payloads for greater efficiency
6. Network layer security: Encryption and authentication of communications
7. Quality of service (QoS) capabilities: QoS markings of packets and flow labels that help identify priority traffic,

Nothing changes above the Layer 3 “Network” layer.

Deploying IPv6 changes nothing above the Layer 3 “Network” layer. IPv4 and IPv6 are network layer protocols, and protocols above and below remain the same for either IP version. Problems such as a lack of a session layer with Transmission Control Protocol ( TCP ) continue to exist in IPv6, along with new security issues of IPv6 fragmentation. In addition, the limitations of multihoming and the exponential growth of the Default Free Zone ( DFZ ) table size are not solved by deploying IPv6. Attacks against any IPv6 network fall within the following areas and are similar to those related to IPv4 attacks,

We have similar security problems but with different countermeasures. For example, instead of IPv4 ARP spoofing, we have IPv6 ND spoofing. Existing network attacks such as Flooding / DDoS, eavesdropping, session hijacking, DNS attacks, man-in-the-middle attacks, and routing security problems are still present with IPv6.

Application-level attacks

The majority of vulnerabilities are at the application layer. Application layer attacks in IPv4 and IPv6 are identical, and security concerns with SQL injections still occur at layers operating over IPv6. However, new IPv6 security considerations such as Dual-Stack-exposures and Tunneling exposures not concerned with IPv4 must be addressed as some of the principal IPv6 security vulnerabilities.

IPv6 Security Vulnerabilities

Running both IPv4 and IPv6 at the same time is called Dual-Stack. A router can support two or more different routed protocols and forward for each type of traffic. The IPv4 and IPv6 protocols can share the same physical node but act independently. Dual stacking refers to the concept known as “ships-in-the-night-routing”; packets from each protocol can pass without affecting one another.

**Avoid Dual Stack when possible**

It is recommended to avoid Dual Stack as the Multi-Protocol world is tricky. The problem may arise if someone configures IPv6 without prior knowledge. All servers and hosts would then expose themselves to IPv6 threats. For example, imagine you have a protected server segment-running IP tables, NIC-level firewalls, and stateful aggregation layer firewalls on the servers.

Best practices are followed, resulting in a protected segment. What you do not control is whether servers have IPv6 enabled. When a router sends IPv6 Router Advertisement ( RA ) messages, these servers will auto-configure themselves and become reachable over IPv6 transport. This may not be a problem with Windows servers. Windows firewall works for both IPv4 and IPv6. Unfortunately, Linux servers have different IP tables for IPv4 and IPv6; Iptable for IPv4 and IP6tables for IPv6.

Linux hosts receive IPv6 RA messages, and some dual-stack Linux hosts with link-local addresses establish outbound IPv6 sessions. The link-local is local to the link, and the first-hop router sends an ICMP reply saying “out of scope.” Most Linux OSs will terminate IPv6 sessions so you can fall back to IPv4.

However, other versions of Linux do not fall back immediately and wait for TCP to time out, causing significant application outages. As a temporary measure, people started to build IPv6 tunnels. As a result, tunnel-related exposure exists. Teredo is the most notorious attack on IPv6. Therefore, all IPv6 tunnels should be blocked by the firewall.

**Pay Close Attention To Tunnels**

IPv4 and IPv6 are not natively compatible with handling mixed networks. However, IPv6 traffic can be carried over IPv4 native networks using tunnels. Tunnels may have security drawbacks, such as reducing visibility into traffic, traversing them, and bypassing firewalls. In addition, an attacker can manipulate the traffic flow by abusing auto-tunneling mechanisms.

Tunnels should be treated with caution. Generally, static tunnels are preferred over dynamic tunnels, and they should only be enabled when explicitly needed. Filtering can also control which hosts can act as tunnel endpoints at the firewall level.

Guide with IPv6 RA

In the following, we address IPv6 RA. IPv6 Router Advertisement (RA) is a key mechanism in IPv6 networks that allows routers to inform neighboring hosts and networks about their presence and provide essential network configuration information. Routers periodically send RA messages, enabling hosts to autoconfigure their network settings, such as IPv6 addresses, default gateways, and other parameters.

The command ipv6 address autoconfig default creates a static route on R2, potentially creating a security flaw in certain use cases.

Use a random addressing scheme instead of a predictable one

The predictability of IPv6 addresses has contributed significantly to the success of reconnaissance attacks against IPv6 subnets. Even though this can be helpful for network administration, it dramatically hinders IPv6 security. In many cases, these attacks can be mitigated by using random addresses, especially for static assignments.

Autoconfiguration once resulted in Layer 3 IPv6 addresses being derived partly from Layer 2 MAC addresses where autoconfiguration is used. As a result, attackers may find it easier to discover hosts. Now, most operating systems can generate random or pseudo-random addresses, so check if this feature is enabled on your endpoints when autoconfiguration is allowed.

IPv6 First Hop Vulnerabilities

• Fake router advertisement ( RA ) messages

IPv6 routers advertise themselves via router advertisement ( RA ) messages. Hosts listen to these messages and can figure out what the first hop/gateway router is. If a host needs to send traffic off its local LAN ( off-net traffic ), it sends it to the first-hop router with the best RA message. In addition, RA messages contain priority fields that can be used for backup routing.

• IPv6 first-hop routers

Intruders can advertise themselves as IPv6 first-hop routers, and any host that believes it will send the intruder its off-net traffic. Once intercepted, attackers have numerous attacking options. It can respond to hosts’ Domain Name System ( DNS ) requests instead of sending them to a legitimate DNS server. Potential DoS attacking hosts. RFC 6101 introduced mitigation techniques in Port ACL, RA-guard lite, and RA-guard.

• IPv6 DHCPv6 attacks

An intruder could pretend to be a DHCPv6 server. If hosts use Stateless Address Autoconfiguration ( SLAAC ) for address configuration, they still require the address of the IPv6 DNS server. Hosts obtain their IPv6 address automatically; it sends out DHCP information requests asking for the IPv6 address of the DNS server. Intruders can intercept and send in Bogus IPv6 for the hostnames that the client is querying for.

• Fake neighbor advertisement messages

When a device receives a neighbor solicitation, it looks into the source address of the message and stores the result in the cache. Excessive neighbor solicitation from an intruder can fill up this cache-causing router ND cache overflow and increased CPU load on the router, overloading the control plane.

Remote neighbor discovery attacks

Remote neighbor discovery occurs when an intruder scans IPv6 subnets with “valid” IPv6 packets, either “valid” TCP SYN packets or PINGs. Unknown directly connected destination IPv6 addresses trigger Router Solicitation neighbor discovery mechanism, causing ND cache and CPU overload. The critical point is an attacker can trigger the attack remotely.

This may not have been a problem with IPv4, as subnets are small. However, in IPv6, you have large subnets; you can try to scan them and generate neighbor cache problems on the last layer 3 switches.

Input ACL that allows known IPv6 subnets. However, some devices do the ND process before checking the inbound ACL. Check the order of operation in the forwarding path. Control plane policing. Cache limits. Prefix longer than /64. People are using /128 on server subnets. Use with care. It is better to use Inbound ACL and not with longer prefixes. 

 Duplicate address detection ( DAD ) attacks

Autoconfiguration works when hosts create their IPv6 address and send a packet asking if anyone else uses it. An intruder can then reply and say yes, I do, which disables auto-configuration on that LAN.

IPv6 host exposure and IPv6 fragmented DOS attacks

IPv6 has multiple extension headers, offering attackers tremendous options for attack. Potentially, there are too many extension headers attempting to generate fragments. Generating fragments hides the real TCP and UDP port numbers into fragments where firewalls can’t immediately see them. Firewalls should be configured to drop fragmented headers.

1. The hop-by-hop Header tells each switch to inspect and act on this header, which can lead to a great DoS tool.
2. The routing header is the same as the IP source route in IPv4. It should drop by default.

• A key point: Filter on the IPv6 extension headers

Firewalls and ACLs should be able to filter extension headers. However, performing Deep Packet Inspection (DPI) on an IPv6 packet that contains many extension headers is resource-intensive, so firewalls should limit the number of extension headers. 

**Mitigation Strategies:**

1. Network segmentation: By properly segmenting the network and implementing firewalls, organizations can limit the exposure of IPv6 hosts. This approach helps isolate critical assets from threats and reduces the attack surface.

2. Continuous monitoring: Organizations should use network monitoring tools to detect and analyze IPv6 traffic. This ensures the timely detection of potential security incidents and allows for effective response and mitigation.

3. Regular security assessments: Conducting periodic security and penetration testing can help identify vulnerabilities and weaknesses in IPv6 deployments. Addressing these issues promptly can prevent potential host exposure and minimize risks.

4. Proper configuration and patch management: Organizations should ensure that IPv6 devices are appropriately configured and regularly updated with the latest security patches. This reduces the likelihood of misconfigurations and minimizes the risk of known vulnerabilities being exploited.

5. Education and awareness: Organizations should prioritize educating their employees about the risks associated with IPv6 host exposure and provide guidelines for secure IPv6 deployment. This empowers individuals to make informed decisions and helps create a security-conscious culture.

Final Points: IPv6 Host Exposure

IPv6, or Internet Protocol Version 6, is crucial for the continued growth and sustainability of the internet. Unlike its predecessor, IPv4, which uses a 32-bit address space, IPv6 employs a 128-bit address space, allowing for approximately 340 undecillion unique addresses. This expansive address space is essential for accommodating the burgeoning number of internet-connected devices, from smartphones and laptops to smart appliances and IoT gadgets.

One of the key features of IPv6 is its ability to assign a unique public IP address to every device, potentially making them directly reachable from anywhere in the world. While this eliminates the need for NAT (Network Address Translation) and simplifies routing, it also increases the risk of host exposure. Host exposure refers to the vulnerability of devices to unauthorized access or cyber-attacks, as they are more visible on the global internet.

The increased visibility of devices under IPv6 necessitates a reevaluation of network security strategies. Traditional security measures like firewalls and intrusion detection systems must be adapted to account for the unique characteristics of IPv6. Organizations must ensure that their security policies are robust enough to protect against the threats posed by exposed hosts. This includes implementing effective access controls, monitoring network traffic, and keeping all devices and systems up-to-date with the latest security patches.

To mitigate the risks associated with IPv6 host exposure, network administrators should adopt a proactive approach. This includes:

1. **Implementing IPv6 Firewalls:** Ensure that IPv6-specific firewalls are in place to filter traffic and prevent unauthorized access.

2. **Addressing Configuration Management:** Regularly review and update device configurations to ensure they adhere to security best practices.

3. **Conducting Security Audits:** Periodically assess the network infrastructure to identify and address potential vulnerabilities.

4. **Educating Users:** Raise awareness among users about the importance of cybersecurity and the role they play in protecting network assets.