The revocation image integrity is verified with a rollover key that comes prestored on the platform. This is because the Layer 4 information that is used in order to filter TCP and UDP packets is only present in the initial fragment. These topics contain operational recommendations that you are advised to implement. If NTP is used, it is important to explicitly configure a trusted time source and to use proper authentication. Computer security training, certification and free resources. There might only be one isolated VLAN per primary VLAN, and only promiscuous ports can communicate with ports in an isolated VLAN. It also does not allow malicious users to change the configuration register value and access NVRAM. The log is maintained on the Cisco IOS device and contains the user information of the individual who made the change, the configuration command entered, and the time that the change was made. Structured around the three planes into which functions of a network device can be categorized, this document provides an overview of each included feature and references to related documentation. View with Adobe Reader on a variety of devices, View in various apps on iPhone, iPad, Android, Sony Reader, or Windows Phone, View on Kindle device or Kindle app on multiple devices, Monitor Cisco Security Advisories and Responses, Leverage Authentication, Authorization, and Accounting, Buffer Overflow: Detection and Correction of Redzone Corruption, Limit Access to the Network with Infrastructure ACLs, Authentication, Authorization, and Accounting, Fortify the Simple Network Management Protocol, Do Not Log to Console or Monitor Sessions, Cisco IOS Software Configuration Management, Configuration Replace and Configuration Rollback, Cisco IOS Software Resilient Configuration, Configuration Change Notification and Logging, Limit CPU Impact of Control Plane Traffic, Filter BGP Prefixes with Autonomous System Path Access Lists, Routing Protocol Authentication and Verification with Message Digest 5, Features and Traffic Types that Impact the CPU, Access Control with VLAN Maps and Port Access Control Lists, Appendix: Cisco IOS Device Hardening Checklist, Risk Triage for Security Vulnerability Announcements, A Security Oriented Approach to IP Addressing, Protecting Your Core: Infrastructure Protection Access Control Lists, TTL Expiry Attack Identification and Mitigation, Control Plane Protection Feature Guide - 12.4T, Configuring Secure Shell on Routers and Switches Running Cisco IOS, Secure Shell Version 2 Enhancements for RSA Keys, Configuring the Cisco IOS SSH Server to Perform RSA-Based User Authentication, Configuring the Cisco IOS SSH Client to Perform RSA-Based Server Authentication, Recommendations for Creating Strong Passwords, Limiting Access to the Network with Infrastructure ACLs, Management Plane Protection Feature Guide, Identifying Incidents Using Firewall and IOS Router Syslog Events, Logging to Local Nonvolatile Storage (ATA Disk), Troubleshooting, Fault Management, and Logging, Cisco IOS Network Management Command Reference, Digitally Signed Cisco Software Key Revocation and Replacement, Understanding Control Plane Protection (CPPr), PFC3 Hardware-based Rate Limiter Default Settings, Configuring the BGP Maximum-Prefix Feature, Connecting to a Service Provider Using External BGP, Configuring IP Routing Protocol-Independent Features, Limiting the Number of Self-Generating LSAs for an OSPF Process, Transit Access Control Lists: Filtering at Your Edge, Understanding Unicast Reverse Path Forwarding, Configuring DHCP features and IP Source Guard, An Introduction to Cisco IOS NetFlow - A Technical Overview, Understanding Access Control List Logging, Private VLANs (PVLANs) - Promiscuous, Isolated, Community, In Cisco IOS Software Release 12.2(8)T and later, issue the, DHCP services can be disabled if DHCP relay services are not required. Hardening Guide The hardening guide is intended to be a living document and will be updated regularly to reflect the most up-to-date cybersecurity best practices. This example ACL includes comprehensive filtering of IP fragments. Protocols that leverage virtual MAC addresses such as HSRP do not function when the maximum number is set to one. In addition to the community string, an ACL should be applied that further restricts SNMP access to a select group of source IP addresses. However, MD5 authentication is still susceptible to brute force and dictionary attacks if weak passwords are chosen. When the threshold is crossed, the device generates and sends an SNMP trap message. Where appropriate, configuration recommendations are made. Each device that an IP packet traverses decrements this value by one. In previous releases of Cisco IOS software, the command to enable NetFlow on an interface is ip route-cache flow instead of ip flow {ingress | egress}. The generation and transmission of these messages is an exception process. One method to provide this notification is to place this information into a banner message that is configured with the Cisco IOS software banner login command. DISA releases new STIGs at least once every quarter. This information is designed in order to corrupt the ARP cache of other devices. This example illustrates the basic configuration of this feature. In some configurations, a subset of all Internet prefixes can be stored, such as in configurations that leverage only a default route or routes for a provider’s customer networks. Unless specifically required, you are advised to avoid logging at level 7. Information leaks, or the introduction of false information into an IGP, can be mitigated through use of the passive-interface command that assists in controlling the advertisement of routing information. Some feature descriptions in this document were written by Cisco information development teams. If you use IPSec, it also adds additional CPU overhead to the device. CoPP is available in Cisco IOS Software Release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T. In most situations, the AUX port of a device must be disabled in order to prevent unauthorized access. The starting value varies by operating system and typically ranges from 64 to 255. This ACL is applied inbound on the desired interface. This feature uses two methods in order to accomplish this: Memory Threshold Notification and Memory Reservation. If IP options have not been completely disabled via the IP Options Selective Drop feature, it is important that IP source routing is disabled. Additionally, a malicious user can create a denial of service (DoS) condition with repeated attempts to authenticate with a valid username. SSHv1 and SSHv2 are not compatible. Prefix lists should be used where possible in order to ensure network traffic is sent over the intended paths. The TCP and UDP small services must be disabled. Cisco IOS software uses the first listed method that successfully accepts or rejects a user. PACLs can only be applied to the inbound direction on Layer 2 physical interfaces of a switch. These unneeded services, especially those that use User Datagram Protocol (UDP), are infrequently used for legitimate purposes but can be used in order to launch DoS and other attacks that are otherwise prevented by packet filtering. This configuration example illustrates the use of this command: ICMP redirects are used in order to inform a network device of a better path to an IP destination. Similar to VLAN maps, PACLs provide access control on non-routed or Layer 2 traffic. The SSH server computes a hash over the public key provided by the user. Refer to Configuring Accounting for more information about the configuration of AAA accounting. It is important that events in the management and data planes do not adversely affect the control plane. This ensures that the device on the remote end of the connection is still accessible and that half-open or orphaned connections are removed from the local Cisco IOS device. TACACS+ authentication, or more generally AAA authentication, provides the ability to use individual user accounts for each network administrator. Introduced in Cisco IOS Software Release 12.3(4)T, the CPU Thresholding Notification feature allows you to detect and be notified when the CPU load on a device crosses a configured threshold. See the Authentication, Authorization, and Accounting section of this document for more information about how to leverage AAA. If the strict host key checking flag is enabled on the client, the client checks whether it has the host key entry that corresponds to the server preconfigured. Cisco IOS software provides functionality in order to specifically filter ICMP messages by name or type and code. TACACS+ authentication can be enabled on a Cisco IOS device with a configuration similar to this example: The previous configuration can be used as a starting point for an organization-specific AAA authentication template. Without PVLANs, all devices on a Layer 2 VLAN can communicate freely. This feature often requires coordination from peering routers; however, once enabled, it can completely defeat many TCP-based attacks against BGP. The ACL counters can be cleared by with the clear ip access-list counters acl-name EXEC command. SSH Version 1.99 allows both SSHv1 and SSHv2 connections. IP Source Guard uses information from DHCP snooping to dynamically configure a port access control list (PACL) on the Layer 2 interface, denying any traffic from IP addresses that are not associated in the IP source binding table. Added in Cisco IOS Software Release 15.0(1)M for the Cisco 1900, 2900, and 3900 Series routers, the Digitally Signed Cisco Software feature facilitates the use of Cisco IOS Software that is digitally signed and thus trusted, with the use of secure asymmetrical (public-key) cryptography. Usernames, passwords, and the contents of access control lists are examples of this type of information. Instead, you are advised to send logging information to the local log buffer, which can be viewed with the show logging command. If you’re building a web server, for example, you’re only going to want web … This interface command has to be applied on the ingress interface and it instructs the forwarding engine to not inspect the IP header. If the decrypted hash matches the calculated image hash, the image has not been tampered with and can be trusted. For switches that support booting from sdflash, security can be enhanced by booting from flash and disabling sdflash with the “no sdflash” configuration command. However, within the data plane itself, there are many features and configuration options that can help secure traffic. The Management Plane Protection (MPP) feature in Cisco IOS software can be used in order to help secure SNMP because it restricts the interfaces through which SNMP traffic can terminate on the device. This standard was written to provide a minimum standard for the baseline of Window Server Security and to help Administrators avoid some of the common configuration flaws that could leave systems more exposed. First Hop Redundancy Protocols (FHRPs) provide resiliency and redundancy for devices that act as default gateways. These subsections provide an overview of the most important IGP security features. Because of the threat posed by unauthenticated FHRPs, it is recommended that instances of these protocols use MD5 authentication. This example configuration enables the Cisco IOS SSH server to perform RSA-based user authentication. The information in this document was created from the devices in a specific lab environment. Hardening is to make system hard to protect from unauthorized access and is an on-going process of providing security. In order to accomplish this, issue the. This type of filtering is traditionally performed by firewalls. Network Administration: Hardening Your Network, How to Create a Data Frame from Scratch in R, How to Fill Areas in Minecraft with the Fill Command. The Internet Control Message Protocol (ICMP) was designed as a control protocol for IP. Refer to TTL Expiry Attack Identification and Mitigation for more information on mitigating TTL expiry-based attacks. This checklist is a collection of all the hardening steps that are presented in this guide. In Cisco IOS Software Release 12.3(7)T and later, the Configuration Replace and Configuration Rollback features allow you to archive the Cisco IOS device configuration on the device. Control Plane Protection (CPPr), introduced in Cisco IOS Software Release 12.4(4)T, can be used in order to restrict or police control plane traffic that is destined to the CPU of the Cisco IOS device. OSPF does not utilize Key Chains. In Cisco IOS Software Release 12.3(4)T and later, you can use the ACL Support for the Filtering IP Options feature in a named, extended IP access list in order to filter IP packets with IP options present. It is recommended that a limit be configured for each BGP peer. This makes it possible to correlate and audit network and security events across network devices more effectively. It should also be noted that RSVP, Multiprotocol Label Switching Traffic Engineering, IGMP Versions 2 and 3, and other protocols that use IP options packets might not be able to function properly if packets for these protocols are dropped. Unlike the passive-interface router configuration command, routing occurs on interfaces once route filtering is enabled, but the information that is advertised or processed is limited. This configuration example shows how to enable this feature with the memory free low-watermark global configuration command. The configuration of PVLANs makes use of primary and secondary VLANs. Specifically, portions of the IP and TCP headers, TCP payload, and a secret key are used in order to generate the digest. It is recommended that organizations filter IP packets with low TTL values at the edge of the network. Version 5 is the most commonly used version of NetFlow, however, version 9 is more extensible. With Cisco IOS software, it is possible to send log messages to monitor sessions - monitor sessions are interactive management sessions in which the EXEC command terminal monitor has been issued - and to the console. The Cisco Catalyst 6500 Series Supervisor Engine 32 and Supervisor Engine 720 support platform-specific, hardware-based rate limiters (HWRLs) for special networking scenarios. You need to have knowledge of a vulnerability before the threat it can pose to a network can be evaluated. This CoPP policy drops transit packets that are received by a device when any IP options are present: This CoPP policy drops transit packets received by a device when these IP options are present: In the preceding CoPP policies, the access control list entries (ACEs) that match packets with the permit action result in these packets being discarded by the policy-map drop function, while packets that match the deny action (not shown) are not affected by the policy-map drop function. The created digest is then stored in TCP option Kind 19, which was created specifically for this purpose by RFC 2385 . Organizations that have started to deploy IPv6should include appropriate IPv6 configuration in their hardening guidelines (or call for IPv6 to be disabled, as improperly configured net… After the required connections have been permitted, all other traffic to the infrastructure is explicitly denied. VACLs, or VLAN maps that apply to all packets that enter the VLAN, provide the capability to enforce access control on intra-VLAN traffic. Transit ACLs are also an appropriate place in which to implement static anti-spoofing protections. Although most of this document is devoted to the secure configuration of a Cisco IOS device, configurations alone do not completely secure a network. If TACACS+ were to become completely unavailable, each administrator can use their local username and password. Notice that any use of the system can be logged or monitored without further notice and that the resulting logs can be used as evidence in court. But since … Prior to this feature, there were two types of passwords: Type 0, which is a cleartext password, and Type 7, which uses the algorithm from the Vigen re cipher. If you cannot fully prevent the use of Type 7 passwords, consider these passwords obfuscated, not encrypted. This configuration example limits log messages that are sent to remote syslog servers and the local log buffer to severities 6 (informational) through 0 (emergencies): Refer to Troubleshooting, Fault Management, and Logging for more information. The filtering provided by tACLs is beneficial when it is desirable to filter traffic to a particular group of devices or traffic that transits the network. For this reason, TACACS+ should be used in preference to RADIUS when TACACS+ is supported by the AAA server. This allows the administrator additional control over a device and how the device is accessed. When you do not depend on a single shared password, the security of the network is improved and your accountability is strengthened. Users are the weakest link in any network security scenario. The Hardening Guide adopts standard security and privacy controls and maps them to each of the recommendations. The configuration of a secondary VLAN as an isolated VLAN completely prevents communication between devices in the secondary VLAN. Once a VLAN map is configured, all packets that enter the LAN are sequentially evaluated against the configured VLAN map. This functionality can be used in attempts to route traffic around security controls in the network. It is critical that SNMP be properly secured in order to protect the confidentiality, integrity, and availability of both the network data and the network devices through which this data transits. This is critical for vty lines because they are accessible via the network. This example ACL, which must be used with the access control entries (ACEs) from previous examples, allows pings from trusted management stations and NMS servers and blocks all other ICMP packets: The filter process for fragmented IP packets can pose a challenge to security devices. Cisco IOS Software Release 12.3(4)T added support for the use of ACLs to filter IP packets based on the IP options that are contained in the packet. The distribute-list command is available for OSPF, but it does not prevent a router from propagating filtered routes. Control Plane Policing (CoPP). In the previous CoPP example, the ACL entries that match the unauthorized packets with the permit action result in a discard of these packets by the policy-map drop function, while packets that match the deny action are not affected by the policy-map drop function. When appropriate, you are advised to use views to limit users of SNMP to the data that they require. Cisco IOS software evaluates these non-initial fragments against the ACL and ignores any Layer 4 filtering information. Port Security can use dynamically learned (sticky) MAC addresses to ease in the initial configuration. Community VLANs must be used in order to group servers that need connectivity with one another, but where connectivity to all other devices in the VLAN is not required. A firewall is a security-conscious router that sits between your network and the outside world and prevents Internet users from wandering into your LAN and messing around. Note that the ACL Support for Filtering IP Options feature can be used only with named, extended ACLs. The community VLAN, VLAN 12, is a secondary VLAN to primary VLAN 20. This includes interfaces that connect to other organizations, remote access segments, user segments, and segments in data centers. This is possible with OSPF if you use the Link State Database Overload Protection feature. The CoPP feature can also be used in order to restrict IP packets that are destined to the infrastructure device. There are many tools available that can easily decrypt these passwords. This example configuration enables the use of RSA keys with SSHv2 on a Cisco IOS device: Refer to Secure Shell Version 2 Enhancements for RSA Keys for more information on the use of RSA keys with SSHv2. This is a list of additional services that must be disabled if not in use: In order to set the interval that the EXEC command interpreter waits for user input before it terminates a session, issue the exec-timeout line configuration command. The use of Type 7 passwords should be avoided unless required by a feature that is in use on the Cisco IOS device. Dynamic Address Resolution Protocol (ARP) Inspection (DAI) mitigates attack vectors that use ARP poisoning on local segments. Cisco differentiates these use cases: These sections describe each scenario in detail: Note: The vstack command was introduced in Cisco IOS Release 12.2(55)SE03. User Accounts. You can often run an Interior Gateway Protocol (IGP) in order provide this view. The security configuration framework is designed to help simplify security configuration while still allowing enough flexibility to allow you to balance security, productivity, and user experience. Many protocols are used in order to carry sensitive network management data. Promiscuous ports can communicate with all other ports in the primary and secondary VLANs. Integrated in 12.4(15)T and originally introduced in 12.0(26)S, the Logging to Local Nonvolatile Storage (ATA Disk) feature enables system logging messages to be saved on an advanced technology attachment (ATA) flash disk. This kind of communication can allow an attacker to pose as an FHRP-speaking device to assume the default gateway role on the network. If password recovery is not required, then an administrator can remove the ability to perform the password recovery procedure using the no service password-recovery global configuration command; however, once the no service password-recovery command has been enabled, an administrator can no longer perform password recovery on a device. Instead, the area filter-list command can be used. Refer to IOS SNMP Command Reference for more information about this feature. Filtering packets based on TTL values can also be used in order to ensure that the TTL value is not lower than the diameter of the network, thus protecting the control plane of downstream infrastructure devices from TTL expiry attacks. Refer to Deploying Control Plane Policing for more information about the CoPP feature. Additional information about filtering unused addresses is available at the Bogon Reference Page . If this information is disclosed to a malicious user, the device can become the target of an attack, compromised, and used in order to perform additional attacks. This EIGRP example filters outbound advertisements with the distribute-list command and a prefix list: This EIGRP example filters inbound updates with a prefix list: Refer to Configuring IP Routing Protocol-Independent Features for more information about how to control the advertising and processing of routing updates. You are advised to send logging information to a remote syslog server. Refer to Secure ROMMON Configuration Example for more information about this feature. If you configure these types of ACLs, seek an up-to-date reference that is conclusive. This command configures a Cisco IOS device for SNMPv3 with an SNMP server group AUTHGROUP and enables only authentication for this group with the auth keyword: This command configures a Cisco IOS device for SNMPv3 with an SNMP server group PRIVGROUP and enables both authentication and encryption for this group with the priv keyword: This command configures an SNMPv3 user snmpv3user with an MD5 authentication password of authpassword and a 3DES encryption password of privpassword: Note that snmp-server user configuration commands are not displayed in the configuration output of the device as required by RFC 3414; therefore, the user password is not viewable from the configuration. Cisco IOS devices have a limited number of vty lines; the number of lines available can be determined with the show line EXEC command. Refer to Named Method Lists for Authentication for more information about the configuration of Named Method Lists. If a security incident is able to undermine the functions of the management plane, it can be impossible for you to recover or stabilize the network. ICMP redirects are disabled with the interface configuration no ip redirects command , as shown in the example configuration: IP Directed Broadcasts make it possible to send an IP broadcast packet to a remote IP subnet. The ability of a network to properly forward traffic and recover from topology changes or faults is dependent on an accurate view of the topology. Any method used in order to access the console port of a device must be secured in a manner that is equal to the security that is enforced for privileged access to a device. A typical network operating system can support dozens of different types of network services: file and printer sharing, web server, mail server, and many others. The first type of traffic is directed to the Cisco IOS device and must be handled directly by the Cisco IOS device CPU. The management plane is used in order to access, configure, and manage a device, as well as monitor its operations and the network on which it is deployed. Refer to Reserve Memory for Console Access for more information about this feature. While this does mitigate the threats related to IP options for the local device, it is possible that downstream devices could be affected by the presence of IP options. This causes non-initial fragments to be evaluated solely on the Layer 3 portion of any configured ACE. SNMP Views are a security feature that can permit or deny access to certain SNMP MIBs. A malicious user can exploit the ability of the router to send ICMP redirects by continually sending packets to the router, which forces the router to respond with ICMP redirect messages, and results in an adverse impact on the CPU and performance of the router. This is an example of NetFlow output from the CLI. The presence of IP options within a packet can also indicate an attempt to subvert security controls in the network or otherwise alter the transit characteristics of a packet. The implementation of iACLs can be made easier through the use of distinct addressing for network infrastructure devices. Refer to An Introduction to Cisco IOS NetFlow - A Technical Overview for a technical overview of NetFlow. Fragmentation is also often used in attempts to evade detection by intrusion detection systems. Introduced in Cisco IOS Software Release 12.3(8)T1, the Memory Leak Detector feature allows you to detect memory leaks on a device. Commonly, these anti-spoofing ACLs are applied to ingress traffic at network boundaries as a component of a larger ACL. Production and special key types have an associated key version that increments alphabetically whenever the key is revoked and replaced. The level specified indicates the lowest severity message that is sent. Use the global configuration commands no logging console and no logging monitor in order to disable logging to the console and monitor sessions. The current running state of this feature can be displayed with the show secure boot EXEC command. This document gives you a broad overview of the methods that can be used in order to secure a Cisco IOS system device. Process switched traffic normally consists of two different types of traffic. However, SSH must still be enforced as the transport even when IPSec is used. This ensures that the device on the remote end of the connection is still accessible and that half-open or orphaned connections are removed from the local IOS device. If a network absolutely requires directed broadcast functionality, its use should be controlled. Originally intended to export traffic information to network management applications, NetFlow can also be used in order to show flow information on a router. 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