Posts filed under Security

Cisco ISE MAC Addresss Database Clean Up

Imagine having 15.000+ MAC addresses in a Cisco ISE database. All these MAC addresses are used to gain access to wireless networks protected with WPA2-PSK and MAC-filtering. But how to make sure that they are all (still) valid?

Remove MAC Addresses After Change In Authentication

Finally, the time has come to implement 802.1x on the wireless network for a substantial amount of these devices. These devices are consist mainly of Windows machines or Thin Clients. Both of those are managed through either the Microsoft Active Directory or a Thin Client Management Suite. So, applying setting related to 802.1x are pretty straight forward to distribute. There are however some Windows / Thin client devices that will remain on the MAC-filtering wifi networks for numerous reasons.

After a few tests the migration of the new 802.1x devices has started, but is leaving us with a MAC Address database filled with addresses that can be removed, since they are no longer used…. But how to do that? Cisco ISE has a lot of features, and is capable of generating rich reports about almost everything. However it has no way of reporting on dot1x devices that might still remain in the MAC address database as well. That is where I had to become creative.

First I explored the Cisco ISE Monitoring API, but that only gives active connections. There’s no way of exploring past (successful) authentications/authorizations. I needed a way to get current and past successful dot1x authentications and compare the MAC addresses associated with those entries to the MAC address database, and remove those from that database.

Eventually, I found two paths to accomplish this; First through the reporting module. There you can export all RADIUS authentications to CSV. Filtering these results in Excel, or through Python scripting, you are able to extract the MAC Addresses that successfully authenticated with dot1x. Feed these MAC addresses to a script and remove them through the Cisco ISE ERS API. Or if you’ve got nothing else to do; do it by hand.

The other path is by following the syslog output and parsing that feed. The downside to this is that you have to have syslog file access or add an additional syslog server to Cisco ISE that you may access (e.g. your scripting machine). The syslog version makes a a bit more tricky, since the (syslog)log lines are very long and you have to combine the correct lines to get the full message. Parsing CSV is much easier, so I followed that path first.

Dormant/Obsolete MAC Addresses

Another issue with static MAC addresses (and even local accounts) is that they tend to remain indefinitely in the MAC database. Lang after devices have been decommissioned, the MAC address remains. Which leaves a security hole to be exploited.

By using the generated ‘RADIUS Authentications’ reports over a longer time (e.g. 90 days) you can do a cross reference with MAC addresses in the database and recent successful authentications of that MAC address.
There are some caveats though;

  1. you need a session-timeout on the network (either statically defined on the network device) or by RADIUS return attribute, so that devices have to re-authenticate periodically. Otherwise you might not see a valid device in the logging and removed it by mistake.

  2. RADIUS Reporting goes only 30 days back, so you have to combine several (scheduled) reports to achieve a longer time span. There used to be a custom time frame option, but seems to have disappeared in version 2.6

Cisco ISE v2.6 and Google ChromeOS

While playing around with the new Cisco Identity Service Engine (ISE) v2.6 (patch2) I stumbled upon a security feature while testing Wireless 802.1x access with an Acer Chromebook (ChromeOS v75.0.3770.144). When connecting to the 802.1x enabled SSID the connection failed, while other devices (Windows 10, Apple iOS and MacOS) connected just fine.

The problem is the client EAP handshake and usually this relates to untrusted server certificates. This happens to me a lot since I use different RADIUS services for my testing SSID’s.
So after clearing the SSID settings (forget) on the Chromebook it should work, but it didn’t.

The logging showed that the EAP handshake failed because the client didn’t offer a suitable cipher to the ISE server.

Turns out that Cisco ISE v2.6 has SHA1 disabled by default, and you need to enable it in:

Administration -> System -> Settings -> Security Settings

With the setting ‘Allow SHA1 Ciphers’, and ‘Allow only TLS_RSA_WITH_AES_128_CBC_SHA’ the Chromebook was able to connect to the 802.1x enabled SSID using old/depricated ciphers.

Now I wonder why the Chromebook still uses SHA1 based ciphers for secure communications, since Google Chrome started to abandon SHA1 as one of the first browsers….

Even installing the ‘Powerwash for added security’ feature in ChromeOS didn’t enable or add stronger ciphers on the Chromebook.

Posted on July 31, 2019 and filed under Tips'n Tricks, Security.

Juniper SRX, Virtual Routers, and SNMPv3

In this continuing story about Junos and virtual routers an episode about SNMPv3.

A simple SNMPv3 config for Junos would be the following:

set snmp v3 usm local-engine user authpriv authentication-md5 authentication-password My_Password_01
set snmp v3 usm local-engine user authpriv privacy-aes128 privacy-password My_Password_02
set snmp v3 vacm security-to-group security-model usm security-name v3test group v3test
set snmp v3 vacm security-to-group security-model usm security-name authpriv group v3test
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level authentication read-view v3testview
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level authentication write-view v3testview
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level authentication notify-view v3testview
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level privacy read-view v3testview
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level privacy write-view v3testview
set snmp v3 vacm access group v3test default-context-prefix security-model any security-level privacy notify-view v3testview
set snmp v3 snmp-community v3test security-name v3test
set snmp view v3testview oid system include
set snmp view v3testview oid .1 include

Authenticating with the correct credentials (U: authpriv, P: My_Password_01) will give results in a single (default) virtual router.

Using this config in a multiple VR environment will result in Authentication and/or authorization errors. Reason being the not using the root/single VR configuration.

Adding some details to the config, AND altering the actual SNMPv3 query will solve that.

set snmp v3 usm local-engine user authpriv authentication-md5 authentication-password My_Password_01
set snmp v3 usm local-engine user authpriv privacy-aes128 privacy-password My_Password_02
set snmp v3 vacm security-to-group security-model usm security-name authpriv group v3test
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level authentication read-view v3testview
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level authentication write-view v3testview
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level authentication notify-view v3testview
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level privacy read-view v3testview
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level privacy write-view v3testview
set snmp v3 vacm access group v3test context-prefix DEFAULT security-model any security-level privacy notify-view v3testview
set snmp v3 snmp-community v3test security-name v3test
set snmp view v3testview oid system include
set snmp view v3testview oid .1 include
set snmp routing-instance-access access-list DEFAULT

The main differences are:

  • context-prefix <VR-NAME>
  • snmp routing-instant-access access-list <VR-NAME>

Having done that, AND adding a context parameter to the actual query will give the correct results.

Posted on June 27, 2018 and filed under Junos, Security, Tips'n Tricks.

Juniper SRX, Routing Instances, and Syslog Challenges

In the previous post I described the issue I had with routing instances and DHCP-relay, and how I fixed it. It turns out that DHCP-relay wasn't my only problem. Turns out that syslog also stopped at the time I implemented the routing instances.

Syslog-gap

To solve this I needed to inject the route to my syslog server (Splunk) in the global routing instance by using policy options.

set policy-options policy-statement syslog-policy term 10 from instance DEFAULT
set policy-options policy-statement syslog-policy term 10 from route-filter 192.168.20.0/24 exact
set policy-options policy-statement syslog-policy term 10 then accept
set policy-options policy-statement syslog-policy then reject

set routing-options instance-import syslog-policy
Posted on June 25, 2018 and filed under Annoying, Security, Tips'n Tricks.

Juniper SRX, Virtual Routers and DHCP Relay

A couple of weeks ago, I started to implement virtual routers in my SRX300. The reason being a new external subnet that  needed to route to a specific security zone. Using the default VR only wouldn't work because of the (single) default route.

Implementing it was fairly easy. The trouble began this week;

  • Wireless controller not accessible
  • Client with weird behaviour
  • etc.

In my network, I have 1 DHCP server serving multiple internal subnets. The (basic) DHCP relay configuration was:

set forwarding-options dhcp-relay maximum-hop-count 10
set forwarding-options dhcp-relay client-response-ttl 10
set forwarding-options dhcp-relay server-group DHCP_Server 192.168.x.x
set forwarding-options dhcp-relay active-server-group DHCP_Server
set forwarding-options dhcp-relay group clients active-server-group DHCP_Server
set forwarding-options dhcp-relay group clients interface ge-0/0/0.1
set forwarding-options dhcp-relay group clients interface ge-0/0/0.20
set forwarding-options dhcp-relay group clients interface ge-0/0/0.30
set forwarding-options dhcp-relay group clients interface ge-0/0/0.200

Turns out that this stops to function when implementing Virtual Routers. Something I forgot to adjust. And since the DHCP scope on my server was set to a lease-time of 14 days.... That means that problems tend to introduce themselves after a couple of days.....

Anyway, after changing the DHCP relay configuration to include the correct Virtual Router name (DEFAULT) everything worked just fine.

set routing-instances DEFAULT forwarding-options dhcp-relay maximum-hop-count 10
set routing-instances DEFAULT forwarding-options dhcp-relay client-response-ttl 10
set routing-instances DEFAULT forwarding-options dhcp-relay server-group DHCP_Server 192.168.x.x
set routing-instances DEFAULT forwarding-options dhcp-relay active-server-group DHCP_Server
set routing-instances DEFAULT forwarding-options dhcp-relay group clients active-server-group DHCP_Server
set routing-instances DEFAULT forwarding-options dhcp-relay group clients interface ge-0/0/0.1
set routing-instances DEFAULT forwarding-options dhcp-relay group clients interface ge-0/0/0.20
set routing-instances DEFAULT forwarding-options dhcp-relay group clients interface ge-0/0/0.30
set routing-instances DEFAULT forwarding-options dhcp-relay group clients interface ge-0/0/0.200

So. DHCP is a bit like DNS. Both have timers (TTL and lease-time) that might bite you in the butt.

Posted on June 10, 2018 and filed under Annoying, Junos, Security.

Juniper vSRX Firewall and VMWare Workstation 14

For a work related project, I wanted to run the Juniper vSRX firewall (v15.1X49-D110) on my work laptop by using VMWare Workstation Pro 14. Unfortunately, the installation (importing the Juniper vSRX OVA file resulted in a VMWare Workstation crash.

Juniper SRX and DHCP Client Challenge

A couple of years ago I wrote a post about a dual ISP config with a Juniper SRX firewall. At the time I ran into some challenges regarding the DHCP client functionality of the SRX. For some reason it couldn't get a lease from the Ziggo ISP DHCP servers. Any other DHCP server on my local network worked just fine. Since I created a work-around at the time (by using an additional NAT router and static IP addresses) I didn't give it much thought.... Until last week.

Last week I ran into a networking challenge that kinda freaked me out. For some reason my Apple TV wouldn't connect to my NAS, but it could connect to the Internet. For some reason my Apple TV got a public IP address while it was located on my internal network. The public IP address was completely unknown to me. So, WTF was giving my Apple TV a public IP address?

Posted on February 13, 2017 and filed under Internet, Security, Tips'n Tricks, Junos.

Configure NGINX as a Secure Reverse Proxy

NGINX (pronounced as engine-x) is a versatile (reverse) proxy service for Linux which can be used for many purposes. This post gives a relative small and easy example that I use at home for accessing insecure web services in my home. These are:

  • Domoticz
    Free and opensource Domotica software
  • SabNZBd
    Free and opensource software for downloading binaries from usenet. Available for multiple operating systems
  • Sonarr
    (former NZBDrone) is a so-called PVR (personal video recorder) for Usenet users, which checks multiple RSS feeds (also called Indexer) for new episodes of the shows you're following.

These services run on different platforms and are not protected by username/password or encryption. Something that's not done if you want to access this over the Internet.
To get secure access to these services you might want to use a VPN solution into your home, but you can also achieve this by using a reverse proxy that 'protects' these services.

I run my NGINX reverse proxy on Ubuntu Linux, but it will also run on the average Raspberry Pi.

Posted on January 29, 2017 and filed under Internet, Security, Tips'n Tricks.

Internet of Things (IoT) and Ransomware

Unfortunately, and no matter how funny the cartoon may be, this may be what the future is going to bring us if we're not careful.

Below are some of the online appliances (just random picks from Google):

The only item I couldn't find was the Internet-connected broom. But I guess that won't take long. The other items can all be bought with some sort of Internet connectivity, and are therefore potential vulnerable for abuse.

Posted on October 10, 2016 and filed under Annoying, Gadgets, Hardware, Internet, Security.

Why Encryption Matters

John Oliver addresses the need for encryption in an hilarious way. The clip is ~18 minutes, but well worth it.

If you still think that encryption is only used for evil (terrorism, child pornography, etc.), and that governments / security agencies should need (backdoor) access to your data..... Well, I'm not gonna end that sentence.

Posted on April 12, 2016 and filed under Fun, Internet, Privacy, Security, Video.