Category: Cisco Sec

Cisco PPP Authentication

As a network engineer, you most probably already had to do with PPP authentication at least once or two times in your daily operation.  Even more, if you are going for a Cisco certification (and not only) you should know some stuff about PPP authentication. For today, I’ve planned to deal with back-to-back PPP authentication.

For this back to back scenario, we have the following simple topology:

When we talk about PPP authentication on a end-to-end line we are dealing with 3 major authentication method:

– PAP

– CHAP

– EAP

Now, when we think at security, we can easily observe that PAP is the less secure one and CHAP or EAP are the strongest one.

PAP (Password Authetication Protocol) transmits unencrypted ASCII passwords over the network and is therefore considered insecure. It should be used only as a last resort when the remote server does not support a stronger authentication protocol, like CHAP or EAP.
CHAP (Challenge-Handshake Authentication Protocol) is a more secure protocol as it uses a three-way handshake and the shared secret (password) is never sent on the wires. Instead a MD5 hash checksum is calculated based on the share secret and this one is sent as a challenge to the other peer.
EAP (Extensible Authentication Protocol) is an authentication framework, not a specific authentication mechanism. It provides some common functions and negotiation of authentication methods called EAP methods. There are currently about 40 different methods defined.

When we think of PPP authentication direction there are 2 types:

– one way authentication

– two ways authentication

Pretty obvious, no?

OK, enough with the theory. If you need some more deep understanding of PPP, there is always Internet. Next, I will show you some simple example with PPP authetication using PAP, CHAP and EAP.

PAP type authentication

Let’s assume that in the scenario above, R1 is sending a challenge to R2. Very important! From PPP authentication configuration, you don’t have to do anything to response to a challenge. This is done automatically.

R1
username R2 password cisco
int s0/0
encapsulation ppp
ppp authentication pap

R2
int s0/0
encapsulation ppp
ppp pap sent-user R2 password cisco

Actually that’s it. As I said, pretty simple. You configure R1 to send an authentication challenge to R2 with “ppp authentication pap”. R2 has to reply to this challenge with a username and a password defined with “ppp pap sent-user R2 password cisco”. This username and password have to be defined on R1. No matter what user and password you define on challenged part to be sent back, that information you have to define on challenger.

CHAP authentication type

Configuring CHAP is even easier. In the example below, I will configure R2 to send a CHAP challenge to R1

R1
username R2 password cisco
int s0/0
encapsulation ppp

R2
username R1 password cisco
int s0/0
encapsulation ppp
ppp authentication chap

By default, CHAP is sending the router hostname the user in the three-way handshake process, so there is no need to specify what user to send like in PAP method. As I said before, this method is more secure than PAP.

EAP authetication type

To be honest I didn’t saw too many PPP connections being authenticated with EAP, but is there and I saw some CCIE lab topics so, you should keep an eye on it. Like the other two method this one is easy to implement and is offering more secure level of authetication than PAP.

R1
username R2 password cisco
int s0/0
encapsulation ppp
ppp authentication eap
ppp eap identity R1
ppp eap password cisco
ppp eap local

R2
username R1 password cisco
int s0/0
encapsulation ppp
ppp authentication eap
ppp eap identity R2
ppp eap password cisco
ppp eap local

I believe that the command syntax is telling pretty much all there is. With “identity” you define the user to be send to the peer, “password” it what word is saying and last option “local” is the quite important. By default EAP needs a RADIUS server for authentication. If you don’t have one (exams, quick testing…) then you want EAP to use local database instead of RADIUS.

This  are the basics of PPP authentication. Even if there are not so much in use, try to remember this small steps as you might need them sometimes.

Other Authentication Related Articles in Internet

Converting from old to new with the PIX to ASA Migration Tool

Digging through Internet I’ve found a very good article from David Davis explaining how to make your life easier when migrating from PIX to ASA.

The important thing to note about PIX and ASA configurations are that they are different. In other words, to do one thing on a PIX requires a different command on an ASA. The ASA uses a more “IOS-like” configuration where the PIX has its own “PIX-OS” configuration. Here are just some of the differences between the two:

  • The ASA is different hardware and has different interface names.
  • The ASA uses sub-interface commands, like the Cisco IOS.
  • A PIX will use FIXUP commands for application inspection whereas the ASA will use policy maps.
  • On the PIX,outbound and conduit commands are used versus access lists on the ASA.

There are two ways to perform this conversion — manually or by using the automatic migration tool. You may want to perform the conversion manually if you want more granular control, but Cisco offers a PIX to ASA Migration Tool that can perform this automatically. Let’s look at how it works.

Read the full article at: Converting from old to new with the PIX to ASA Migration Tool


Cisco: CUCM DoS Vulnerabilities

Cisco Unified Communications Manager (formerly Cisco CallManager) contains multiple denial of service (DoS) vulnerabilities that if exploited could cause an interruption of voice services. The Session Initiation Protocol (SIP), Skinny Client Control Protocol (SCCP) and Computer Telephony Integration (CTI) Manager services are affected by these vulnerabilities.

To address these vulnerabilities, Cisco has released free software updates for select Cisco Unified Communications Manager versions. There is a workaround for of one the vulnerabilities.

The following products are affected by vulnerabilities that are described in this advisory:

* Cisco Unified Communications Manager 4.x
* Cisco Unified Communications Manager 5.x
* Cisco Unified Communications Manager 6.x
* Cisco Unified Communications Manager 7.x

Administrators can mitigate the SCCP- and SIP-related vulnerabilities by implementing filtering on screening devices to permit access to TCP ports 2000 and 2443, and TCP and UDP ports 5060 and 5061 only from networks that require SCCP and SIP access to Cisco Unified Communications Manager appliances.

It is possible to mitigate the CTI Manager vulnerability by disabling the CTI Manager service t is not necessary; however, this workaround will interrupt applications that reply on the CTI Manager service. Administrators can also mitigate the vulnerability by implementing filtering on screening devices to permit access to TCP port 2748 only from networks that require access to the CTI Manager service.

This advisory is posted at http://www.cisco.com/warp/public/707/cisco-sa-20100303-cucm.shtml

Multiple Vulnerabilities in Cisco ASA 5500 Series

Cisco ASA 5500 Series Adaptive Security Appliances are affected by the following vulnerabilities:

* TCP Connection Exhaustion Denial of Service Vulnerability
* Session Initiation Protocol (SIP) Inspection Denial of Service Vulnerabilities
* Skinny Client Control Protocol (SCCP) Inspection Denial of Service Vulnerability
* WebVPN Datagram Transport Layer Security (DTLS) Denial of Service Vulnerability
* Crafted TCP Segment Denial of Service Vulnerability
* Crafted Internet Key Exchange (IKE) Message Denial of Service Vulnerability
* NT LAN Manager version 1 (NTLMv1) Authentication Bypass Vulnerability

These vulnerabilities are not interdependent; a release that is affected by one vulnerability is not necessarily affected by the others.

There are workarounds for some of the vulnerabilities disclosed in this advisory.

Cisco has released free software updates that address these vulnerabilities.

This advisory is posted at http://www.cisco.com/warp/public/707/cisco-sa-20100217-asa.shtml

Cisco FWSM SCCP Inspection DoS Vulnerability

A vulnerability exists in the Cisco Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers that may cause the Cisco FWSM to reload after processing a malformed Skinny Client Control Protocol (SCCP) message. The vulnerability exists when SCCP inspection is enabled.

Cisco has released free software updates that address this vulnerability.

All non-fixed 4.x versions of Cisco FWSM Software are affected by this vulnerability if SCCP inspection is enabled. SCCP inspection is enabled by default.

To check if SCCP inspection is enabled, issue the show service-policy | include skinny command and confirm that the command returns output. Example output follows:

fwsm#show service-policy | include skinny
Inspect: skinny , packet 0, drop 0, reset-drop 0

If SCCP inspection is not required, this vulnerability can be mitigated by disabling it. Administrators can disable SCCP inspection by issuing the no inspect skinny command in class configuration sub-mode within the policy map configuration. If SCCP inspection is required, there are no workarounds.

Cisco has released free software updates that address this vulnerability. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

This advisory is posted at http://www.cisco.com/warp/public/707/cisco-sa-20100217-fwsm.shtml