Cisco Router Device Router Security Report

Introduction

Nipper performed a security audit of the Cisco Router Router on Friday 17 August 2007. This report details the security-related issues identified during the security audit, the impact of each issue and any recommendations. The configuration settings of Router are detailed in the device configuration section. The appendix section details further information that is relevent to the Router device configuration.

Security Audit

Introduction
Software Version
Inbound TCP Connection Keep Alives
Connection Timeout
Auxiliary Port
IP Source Routing
HyperText Transport Protocol Service
Access Control Lists
Logging
Cisco Discovery Protocol
Classless Routing
Minimum Password Length
BOOTP
Service Password Encryption
Login Banner
Domain Lookups
Packet Assembler / Disassembler

Device Configuration

Introduction
General
Domain Name Settings
Time Zone Settings
Services
HyperText Transfer Protocol
Lines
Interfaces

Appendix

Abbreviations
Common Ports
Logging Severity Levels
Time Zones
Nipper Details

Security Audit

Introduction

Nipper performed a security audit of the Cisco Router device Router and 16 security-related issues were identified. This section describes the security-related issues identified during the audit.

Software Version

Observation: It is critically important that software be regularly maintained with patches and upgrades in order to help mitigate the risk of an attacker exploiting a known software vulnerability. Furthermore, additional security features and other functionality are normally added or extended with each software revision.

Nipper determined that the Cisco Router Router was running the out of date software Internet Operating System (IOS) version 12.3. Some of the known vulnerabilities for this software version are listed in Table 1.

Table 1: Potential software vulnerabilities
Description	CVE Reference	Bugtraq ID
Telnet remote denial of service	CVE-2004-1464	11060
IPv4 TCP listener denial of service	CVE-2007-0479	22208

It is worth noting that Nipper used the version number detailed in the device configuration to identify the potential vulnerabilities, and patches may have already been applied. Additionally, a specific device configuration may be required in order for the device to become vulnerable.

Impact: The vulnerabilities listed in Table 1 could allow an attacker to perform a Denial of Service (DoS) attack.

Ease: Exploit code is widely available on the Internet for known Cisco Router vulnerabilities.

Recommendation: Nipper strongly recommends that the software be updated and patched to the latest software version. Furthermore, Nipper recommends that the current patch policy be reviewed.

Inbound TCP Connection Keep Alives

Observation: Connections to a Cisco Router device could become orphaned if a connection becomes disrupted. An attacker could attempt a DoS attack against a Cisco Router by exhausting the number of possible connections. Transmission Control Protocol (TCP) keep alive messages can be configured to confirm that a remote connection is valid and then terminate any orphaned connections.

Nipper determined that TCP keep alive messages are not sent for connections from remote hosts.

Impact: An attacker could attempt a DoS by exhausting the number of possible connections.

Ease: Tools are available on the Internet that can open large numbers of TCP connections without correctly terminating them.

Recommendation: Nipper recommends that TCP keep alive messages be sent to detect and drop orphaned connections from remote systems. TCP keep alive messages can be enabled for connections from remote systems using the following command:

service tcp-keepalives-in

Connection Timeout

Observation: Connection timeouts can be configured for a number of the device services. If a timeout were configured on an administrative service, an administrator that did not correctly terminate the connection would have it automatically closed after the timeout expires. However, if a timeout is not configured, or is configured to be a long timeout, an unauthorised user may be able to gain access using the administrator's previously logged-in connection.

Nipper identified three connection settings that were not configured to timeout within ten minutes, these are listed in Table 2.

Table 2: Connections with inadequate timeout periods
Connection	Timeout
Console line 0	No Timeout
Auxiliary line 0	No Timeout
VTY lines 0 to 4	No Timeout

Impact: An attacker who was able to gain access to a connection that had not expired, would be able to continue using that connection. A connection could be a console port on the device that was not correctly terminated or a remote administrative connection.

Ease: The attacker would have to gain physical access to the device to use the console port, or gain remote access to an administration machine that is attached to the port. To gain access to remote connections, an attacker would have to be able to intercept network traffic between the client and Router. The attacker would then have to take over the connection, which could be very difficult with some services. Tools are available on the Internet that would facilitate the monitoring of network connections.

Recommendation: Nipper recommends that a timeout period of ten minutes be configured for connections to the device Router.

Auxiliary Port

Observation: The auxiliary port's primary purpose is to provide a remote administration capability. It can allow a remote administrator to use a modem to dial into the Cisco device.

Nipper determined that the auxiliary port on the Cisco device Router allowed exec connections and did not appear to have the callback feature configured.

Impact: An attacker may discover the modem number for the device during a war-dial. If an attacker were able to connect to the device remotely, then they may be able to brute-force the login to gain access to the device.

Ease: The attacker would have to first identify the telephone number of the device, probably through a war-dial. A modem attached to a telephone line would have to be attached directly to the Cisco device's auxiliary port. Then the attacker would be able to attach to the device in order to perform a brute-force of the login.

Recommendation: Nipper recommends that, if not required, the auxiliary port exec be disabled. Exec can be disabled on the aux port with the following command:

no exec

If the auxiliary port is required for remote administration, the callback feature can be configured to dial a specific preconfigured telephone number.

IP Source Routing

Observation: IP source routing is a feature whereby a network packet can specify how it should be routed through the network. Cisco routers normally accept and process source routes specified by a packet, unless the feature has been disabled.

Nipper determined that IP source routing was not disabled.

Impact: IP source routing can allow an attacker to specify a route for a network packet to follow, possibly to bypass a Firewall device or an Intruder Detection System (IDS). An attacker could also use source routing to capture network traffic by routing it through a system controlled by the attacker.

Ease: An attacker would have to control either a routing device or an end point device in order to modify a packets route through the network. However, tools are available on the Internet that would allow an attacker to specify source routes. Tools are also available to modify network routing using vulnerabilities in some routing protocols.

Recommendation: Nipper recommends that, if not required, IP source routing be disabled. IP source routing can be disabled by issuing the following IOS command:

no ip source routing

HyperText Transport Protocol Service

Observation: Recent Cisco IOS-based devices support web-based administration using the HTTP protocol. Cisco web-based administration facilities can sometimes be basic but they do provide a simple method of administering remote devices. However, HTTP is a clear-text protocol and is vulnerable to various packet-capture techniques.

The HTTP service was configured and made use of an access-list to restrict access to the device.

Impact: An attacker who was able to monitor network traffic could capture authentication credentials. This issue is made more serious with the enable password being used for authentication as this would give the attacker full administrative access to the device with the captured credentials.

Ease: Network packet and password sniffing tools are widely available on the Internet. Once authentication credentials have been captured it is trivial to use the credentials to log in using the captured credentials.

Recommendation: Nipper recommends that, if not required, the HTTP service be disabled. If a remote method of access to the device is required, consider using HTTPS or Secure Shell (SSH). The encrypted HTTPS and SSH services may require a firmware or hardware upgrade. The HTTP service can be disabled with the following IOS command:

no ip http server

If it is not possible to upgrade the device to use the encrypted HTTPS or SSH services, additional security can be configured. The authentication method can be changed using the following command (where the authentication method is either local, tacacs or aaa):

ip http auth <authentication method>

Access Control Lists

Observation: Access Control List (ACL) are sequential lists of allow and deny Access Control Entries (ACE) that specify whether network traffic should be allowed or dropped. ACLs are used to restrict access to services and network devices, preventing access to services and devices that should not be accessible.

Nipper determined that no ACL were configured.

Impact: If ACEs are not sufficiently restrictive, an attacker may be able to access services or network devices that should not be accessible. Furthermore, an attacker who had compromised a device could install a backdoor which could listen on a network port that was not filtered.

Ease: N/A

Recommendation: Nipper recommends that all ACLs be configured to only allow access to hosts and services from those hosts that require access. However, in certain circumstances, such as a public web server, a more relaxed configuration may be required to allow any host to access specific hosts and services.

Logging

Observation: Logging is an essential component of a secure network configuration. Logging not only assists network administrators to identify issues when troubleshooting, but enables network administrators to react to intrusion attempts or Denial-of-Service attacks. It is therefore critical that logs be monitored, allowing administrators to take immediate action when an attack has been identified. Furthermore, system logs are a key component of a forensic investigation into past intrusions or service disruptions.

Nipper determined that logging had not been configured on Router.

Impact: An attacker could attempt to map and bypass any configured ACL or to gain access to the Cisco Router without network administrators being alerted to the attempts. Furthermore, after an unauthorised intrusion into the network had been detected, it would be more difficult for an investigation to identify the source of the attack or the entry point without access to logs.

Ease: N/A

Recommendation: Nipper recommends that Syslog and Buffered logging be configured on Router. Logging can be enabled with the following command:

logging on

To configure Syslog logging, four things need to be set; a source interface for the Syslog messages to be sent from, one or more Syslog hosts to send messages to, the Syslog logging message severity level and the Syslog facility. The following commands can be used to configure Syslog logging:

logging source-interface <Interface>
logging host <Syslog IP address or hostname>
logging trap <Logging message severity level>
logging facility <Syslog facility>

Buffered logging can be configured with the following command:

logging buffered <Buffer Size> <Logging message severity level>

Cisco Discovery Protocol

Observation: Cisco Discovery Protocol (CDP) is a proprietary protocol that is primarily used by Cisco, but has been used by others. CDP allows some network management applications and CDP aware devices to identify each other on a Local Area Network (LAN) segment. Cisco devices, including switches, bridges and routers are configured to broadcast CDP packets by default. The devices can be configured to disable the CDP service or disable CDP on individual network interfaces.

Nipper determined that even though CDP had been disabled on all active interfaces, the CDP service had not been disabled.

Impact: CDP packets contain information about the sender, such as hardware model information, operating system version and IP address details. This information would allow an attacker to gain information about the configuration of the network infrastructure.

Ease: CDP packets are broadcast to an entire network segment. An attacker could use one of the many publicly available tools to capture network traffic and view the leaked information.

Recommendation: Nipper recommends that, if not required, the CDP service be disabled on the Cisco device Router. If CDP is required, Nipper recommends that CDP be disabled on all interfaces except those that are explicitly required.

The CDP service can be disabled by issuing the following Cisco IOS command:

no cdp run

CDP can be disabled on individual interfaces using the following command:

no cdp enable

In some configurations with IP phones, deployed using either Auto Discovery or Dynamic Host Configuration Protocol (DHCP), the CDP service may need to be enabled. In this situation CDP should be disabled on all network interfaces for which it is not required.

Classless Routing

Observation: Classless routing is enabled by default on Cisco routers. If a router has classless routing enabled and it receives a network packet for which there is no configured route, the router will forward the packet to the best destination. With classless routing disabled, the router would discard any network traffic for which no route is defined.

Nipper determined that classless routing was enabled on Router.

Impact: Network traffic that should not be routed by the router may be routed when classless routing is enabled.

Ease: N/A

Recommendation: Nipper recommends that, if possible, classless routing be disabled. Classless routing can be disabled with the following command:

no ip classless

Minimum Password Length

Observation: Cisco introduced an option from IOS version 12.3(1) which forces user, enable, secret and line passwords to meet a minimum length. This setting was introduced to help prevent the use of short passwords such as "cisco".

Nipper determined that a minimum password length of six characters was configured.

Impact: With a small minimum password length configured, it would be possible for a short password to be used. If an attacker were able to gain a password or through dictionary-based guessing techniques or by a brute-force method, the attacker could gain a level of access to Router.

Ease: A number of dictionary-based password guessing and password brute-force tools are available on the Internet.

Recommendation: Nipper recommends that a minimum password length of at least six characters be configured. The minimum password length can be configured with the following command:

security passwords min-length <length>

BOOTP

Observation: BOOTstrap Protocol (BOOTP) is a datagram protocol that allows compatible hosts to load their operating system over the network from a BOOTP server. Cisco routers are capable of acting as BOOTP servers for other Cisco devices and the service is enabled by default. However, BOOTP is rarely used and may represent a security risk.

Nipper determined that BOOTP was not disabled. However, it is worth noting that not all Cisco devices support BOOTP.

Impact: An attacker could use the BOOTP service to download a copy of the router's IOS software.

Ease: Tools are available on the Internet to access BOOTP servers.

Recommendation: Nipper recommends that, if not required, the BOOTP service be disabled. The following command can be used to disable BOOTP:

no ip bootp server

Service Password Encryption

Observation: Cisco service passwords are stored by default in their clear-text form rather than being encrypted. However, it is possible to have these passwords stored using the reversible Cisco type-7 encryption.

Nipper determined that the Cisco device Router was not running the password encryption service that helps provide a basic level of encryption to passwords that otherwise would be stored in clear-text.

Impact: If a malicious user were to see a Cisco configuration that contained clear-text passwords, they could use the passwords to access the device. However, an attacker who had access to a Cisco configuration file would easily be able to reverse the passwords.

Ease: Even though it is trivial to reverse Cisco type-7 passwords, they do provide a greater level of security than clear-text passwords. Tools are widely available on the Internet that reverse Cisco type-7 passwords.

Recommendation: Nipper recommends that the Cisco password encryption service be enabled. The Cisco password encryption service can be started with the following Cisco IOS command:

service password-encryption

Login Banner

Observation: A banner message can be shown to users who connect to one of the remote management services, such as Telnet. Typically banner messages will include information on the law with regard to unauthorised access to the device, warning users who do not have the authority to access the device about the consequences.

Nipper determined that no login banner was configured.

Impact: Attackers who have gained access to a device could avoid legal action if no banner is configured to warn against unauthorised access.

Ease: N/A

Recommendation: Nipper recommends that a banner be configured that warns against unauthorised access. Banners are configured on Cisco devices using a delimiter character. A delimiter character is specified in the banner command and is used again to mark the end of the banner. The Cisco command to add a login banner, that is presented to users prior to authentication, is:

banner login <delimiter>The banner text<delimiter>

Domain Lookups

Observation: Cisco IOS-based devices support name lookups using the Domain Name System (DNS). However, if a DNS server has not been configured, then the DNS request is broadcast.

Nipper determined that name lookups had not been disabled and no DNS servers had been configured.

Impact: An attacker who was able to capture network traffic could monitor DNS queries from the Cisco Router. Furthermore, Cisco devices can connect to Telnet servers by supplying only the hostname or IP address of the server. A mistyped Cisco command could be interpreted as an attempt to connect to a Telnet server and broadcast on the network.

Ease: It would be trivial for an attacker to capture network traffic broadcast from a Cisco Router. Furthermore, network traffic capture tools are widely available on the Internet.

Recommendation: Nipper recommends that domain lookups be disabled. Domain lookups can be disabled with the following command:

no ip domain-lookup

If domain lookups are required, Nipper recommends that DNS be configured. DNS can be configured with the following command:

ip name-server <IP address>

Packet Assembler / Disassembler

Observation: The Packet Assembler / Disassembler (PAD) service enables X.25 connections between network systems. The PAD service is enabled by default on most Cisco IOS devices but it is only required if support for X.25 links is necessary.

Nipper determined that the PAD service had not been disabled.

Impact: Running unused services increases the chances of an attacker finding a security hole or fingerprinting a device.

Ease: N/A

Recommendation: Nipper recommends that, if not required, the PAD service be disabled. Use the following command to disable the PAD service:

no service pad

Device Configuration

Introduction

This section details the configuration settings of the Cisco Router device Router.

General

Table 3: General device settings
Description	Setting
Hostname	Router
IOS Version	12.3
Service Password Encryption	Disabled
Minimum Password Length	6 characters
IP Source Routing	Enabled
BOOTP	Enabled
Service Config	Disabled
TCP Keep Alives (In)	Disabled
TCP Keep Alives (Out)	Disabled
Cisco Express Forwarding	Enabled
Gratuitous ARPs	Disabled
Classless Routing	Enabled

Domain Name Settings

Table 4: Domain name settings
Description	Setting
Domain Lookup	Enabled

Time Zone Settings

Table 5: Time zone settings
Description	Setting
Time Zone	UTC
UTC Offset	None
Summer Time Zone	Disabled
Authorative Time Source	No

Services

Table 6: Device services
Service	Status
Telnet	Disabled
SSH	Disabled
HTTP	Enabled
Finger	Disabled
TCP Small Services	Disabled
UDP Small Services	Disabled
CDP	Enabled
PAD	Enabled

HyperText Transfer Protocol

Table 7: HTTP configuration
Description	Setting
HTTP Server	Enabled
Authentication Type	Enable Password
Access Class (Access List Number)	Unconfigured

Lines

The Cisco line configuration settings are used to configure administrative access to the device. The console line type is used for accessing the Cisco device directly through a cable attached to the device's console port. The auxiliary lines are used for remote access to the device, typically through attached modems. The Virtual Teletype (VTY) lines are used for access to the device through a remote access service such as SSH or Telnet.

Table 8: Line configuration
Line Type	End Line	Logins	Exec	Authorization	Accounting	Telnet	SSH	Timeout	Exec Timeout	Session Timeout	Absolute Timeout
Console		Allowed	On	Off	Off	Off	Off	0s	0s	0s	0s
Auxiliary		Allowed	On	Off	Off	Off	Off	0s	0s	0s	0s
VTY	4	Allowed	On	Off	Off	Off	Off	0s	0s	0s	0s

Interfaces

Table 9: Interfaces
Interface	Active	IP Address	Proxy ARP	IP Unreachable	IP Redirect	IP Mask Reply	IP Direct Broadcast	NTP	CDP	uREF	MOP
Ethernet0/0	No	None	N/A	N/A	N/A	N/A	N/A	N/A	N/A	Off	N/A
Serial0/0	No	None	N/A	N/A	N/A	N/A	N/A	N/A	N/A	Off	N/A
Serial0/1	No	None	N/A	N/A	N/A	N/A	N/A	N/A	N/A	Off	N/A
Serial0/2	No	None	N/A	N/A	N/A	N/A	N/A	N/A	N/A	Off	N/A

Appendix

Abbreviations

ACE	Access Control Entry
ACL	Access Control List
ARP	Address Resolution Protocol
BID	Bugtraq ID
BOOTP	BOOTstrap Protocol
CDP	Cisco Discovery Protocol
CEF	Cisco Express Forwarding
CVE	Common Vulnerabilities and Exposures
DHCP	Dynamic Host Configuration Protocol
DNS	Domain Name System
DoS	Denial of Service
HTTP	HyperText Transfer Protocol
HTTPS	HyperText Transfer Protocol over SSL
IDS	Intruder Detection System
IOS	Internet Operating System
IP	Internet Protocol
LAN	Local Area Network
MOP	Maintenance Operations Protocol
NTP	Network Time Protocol
PAD	Packet Assembler / Disassembler
SNMP	Simple Network Management Protocol
SSH	Secure Shell
SSL	Secure Sockets Layer
TCP	Transmission Control Protocol
UDP	User Datagram Protocol
UTC	Coordinated Universal Time
VTY	Virtual Teletype

Common Ports

Table 10: Common ports
Service	Port
SSH	22
DHCP	67
HTTP	80
NTP	123
SNMP	126
HTTPS	443

Logging Severity Levels

Table 11: Logging message severity levels
Level	Level Name	Description
0	Emergencies	System is unstable
1	Alerts	Immediate action is required
2	Critical	Critical conditions
3	Errors	Error conditions
4	Warnings	Warning conditions
5	Notifications	Significant conditions
6	Informational	Informational messages
7	Debugging	Debugging messages

Time Zones

Table 12: Common time zone acronyms
Region	Acronym	Time Zone	UTC Offset
Australia	CST	Central Standard Time	+9.5 hours
Australia	EST	Eastern Standard/Summer Time	+10 hours
Australia	WST	Western Standard Time	+8 hours
Europe	BST	British Summer Time	+1 hour
Europe	CEST	Central Europe Summer Time	+2 hours
Europe	CET	Central Europe Time	+1 hour
Europe	EEST	Eastern Europe Summer Time	+3 hours
Europe	EST	Eastern Europe Time	+2 hours
Europe	GMT	Greenwich Mean Time
Europe	IST	Irish Summer Time	+1 hour
Europe	MSK	Moscow Time	+3 hours
Europe	WEST	Western Europe Summer Time	+1 hour
Europe	WET	Western Europe Time	+1 hour
USA and Canada	ADT	Atlantic Daylight Time	-3 hours
USA and Canada	AKDT	Alaska Standard Daylight Saving Time	-8 hours
USA and Canada	AKST	Alaska Standard Time	-9 hours
USA and Canada	AST	Atlantic Standard Time	-4 hours
USA and Canada	CDT	Central Daylight Saving Time	-5 hours
USA and Canada	CST	Central Standard Time	-6 hours
USA and Canada	EDT	Eastern Daylight Time	-4 hours
USA and Canada	EST	Eastern Standard Time	-5 hours
USA and Canada	HST	Hawaiian Standard Time	-10 hours
USA and Canada	MDT	Mountain Daylight Time	-6 hours
USA and Canada	MST	Mountain Standard Time	-7 hours
USA and Canada	PDT	Pacific Daylight Time	-7 hours
USA and Canada	PST	Pacific Standard Time	-3 hours

Nipper Details

This report was generated using Nipper version 0.10.3. Nipper is an Open Source tool designed to assist security professionals and network system administrators securely configure network infrastructure devices. The latest version of Nipper can be found at the following URL:

http://www.sourceforge.net/projects/nipper.