Information gathered from: https://www.armis.com/cdpwn/
The white page can be found here: https://go.armis.com/hubfs/White-papers/Armis-CDPwn-WP.pdf
The purpose of this post is not to exploit the vulnerabilities, but instead to just bring awareness.
First I think it is important to understand what is CDP or Cisco Discovery Protocol, before diving into what was discovered.
For starters, Cisco Discovery Protocol is proprietary to Cisco Systems and was created to help discover Cisco devices in the network landscape. The protocol, runs in the Data Link Layer and behaves by sending a packet every minute to the multicast address 01:00:0C:CC:CC:CC, which any Cisco device will be listening on. It is also important to remember that once received, these messages do not get repeatedly sent. For memory's sake, multicast is the IP service of sending a packet to several hosts, compared to broadcast, which is all hosts. The CDP message contains information about the senders operating system version, the IP address, the interface that sent it, the host name, along with many other details. Thus making this an incredible feature when used correctly.
At the time of this post, there are currently five vulnerabilities disclosed, with four being remote code execution and one being denial of service. These vulnerabilities can lead to a break down of network segmentation, data exfiltration, and main-in-the-middle attacks.
The first vulnerability (CVE-2020-3110) is targeted to the Cisco 8000 Series IP cameras. This is a heap-overflow vulnerability, caused by the mismatch of variable types. In short, the way the CDP process works is that it allocates a buffered spaced based on the length of the Port ID that is passed in and copies this Port ID value to the buffer. However, the size of the Port ID is 16-bit and the size of the buffer is 8-bits, meaning that an attacker can overflow the heap and conduct a remote-code-execution attack.
The second vulnerability (CVE-2020-3111) is targeted to Cisco IP phones. This is a stack-overflow vulnerability caused by the lack of validating the length of the Port ID Type Length Value. The information is directly copied to the stack, which if abused can lead to remote code execution and full control of the VoIP phone, as the CDP daemon process is executed with root privileges.
The third vulnerability (CVE-2020-3118) is targeted to the Cisco IOS-XR Software. This is also a stack-overflow vulnerability, that is caused by a lack of validating certain string fields (Device ID, Port ID, Software Version) in the received CDP packets and how the data is formatted by the sprintf function. In short, the CDP packet's information is copied to the current router's memory. Because of this, an attacker can use format tokens such as %s, %x, or %n to print data to out-of-bounds memory locations. If abused, the vulnerability can lead to remote code execution and once again gain full control over the router.
The fourth vulnerability (CVE-2020-3119) is targeted to the Cisco NX-OS Software. Just like the previous, this is also a stack-overflow vulnerability that targets the negotiation of Power Over Ethernet request fields found in CDP. Here an attacker can send a valid CDP packet continuously that contains a higher power request level than the switch expects, causing a stack overflow. This then allows the attacker to gain full control of the switch.
The last vulnerability (CVE-2020-3120) is targeted to all of the previous devices. In short, this is a Denial of Service attack that is caused by repeatedly crashing the CDP daemon of the given device, causing the device to reboot.
First, I think it is best for us to understand what is external BGP and then dive into how it is insecure and how it can lead to massive problems. Now there are two parties, internal and external routing protocols. An example of an internal routing protocol would be EIGRP (Enhanced Interior Gateway Routing Protocol) or OSPF (Open Shortest Path First), as these routes would be advertised internally or within a given network, but never to the internet. Therefore, external routing protocols are the opposite, they are not to be used within the network, but instead to connect networks together*. This is where BGP comes into play, also known as Border Gateway Protocol, it is the routing protocol of the internet. In simple terms, what we call the internet is the just the massive connection of autonomous systems or AS, which is just the assignment of a publicly known number used to identify a given network or set of IPs. Currently there is an estimated ~84,000 allocated autonomous system networks. BGP also differs from internal routing protocols in that it does not broadcast the entire routing table, instead at boot a nearby peer will hand over their table, then only updates are relayed after. In addition, BGP routes are stored in RIB, or Routing Information Base, where multiple routes to a specific destination are stored. Here, routes are then placed, based on best choice by the router, into the routing table to be used. (The routing table picks the route that uses the least number of AS hops.) This allows for the routing table to be kept small and to update only if needed. Because of the RIB, if a route needs to be removed, but only exists here, then it is silently dropped and no update will be sent. Also, because of this functionality there is no need for RIB entries to time out, so they exist in the base as long as they are valid.
Now, after discussing how BGP works, it is important to talk about its faults and how it has lead to some pretty drastic mishaps. Poor configuration of BGP has plagued the internet since the beginning, but now that more of our lives are connected and better information of proper maintenance is available, it is more important now than ever to educate ourselves. BGP does not appear to be going away anytime soon, so the best thing we can do as security engineers to help protect our organizations is by learning from others mistakes.
Let us take Verizon for example, in June of 2019 a massive route leak impacted huge parts of the Internet. In short, a small Internet Service Provider company named DQE Communications used a BGP optimizer which preferred specific routes over generalized ones and then advertised these routes to their client Allegeny Technologies. From here it was then advertised to Verizon where it was further advertised to the world. Which in return, rerouted traffic to this preferred path causing a massive fault as this route was not prepared to deal with so much traffic. Now the advertisement should have stopped at Verizon, but because it did not around 20% of the Internet was impacted.
In an act to prevent this from occurring, the major thing that should have been implemented is to impose a hard limit of prefixes expected to be received on a BGP session. We will actually explore BGP security more in a later blog so keep following along.
Overall, BGP is the routing protocol of the Internet and while it is the backbone, it does not mean that it is perfect by any means, but we has engineers have to do our best so that another issue like this does not occur.
*For simplicity sake we are going to forget about Internal BGP and will not discuss it. If you want to learn more about how BGP can be used on the internal side visit this link:
Understanding VPNs or Virtual Private Networks is one of the cornerstones of network security. In short, a virtual private network is used to extend, typically a company's private network, across the public network or Internet. This allows devices that reside outside of the network to connect directly to the private networks infrastructure. Now there are different types of VPN services, along with different types of protocols and throughout this post we are going to explore the most common of each.
While there are many specific types of VPNs there are two major types that we will be discussing, which is Client-based and Site-to-Site VPN.
A client-based VPN is probably the one you are most familiar with, this allows a user to connect to a private network remotely. You can use this as a corporate employee while traveling to still access all the necessary services to do your job. However, following within the same lines, companies offer services
CAM table overflows typically are an attack of the past, however that does not mean that we should forget about them. After all once a vulnerability has been found we cannot assume that future devices won't be vulnerable to this threat. In short, CAM table overflows are the idea of an attacker flooding a switch's MAC address table with bogus addresses, thus leading the switch to enter into a flood 'all traffic on all ports' state. This can create a DOS or allow the attacker to sniff traffic.
The best solution to this vulnerability is Port Security and the configuration is quiet simple, all you need is a Cisco switch.
Below we will walk through setting up port security on 24 ports to allow a maximum of 2 MAC addresses, to save already existing MAC addresses, and to shutdown the port if this violation occurs.
Default configuration: Please note that be default Port Security is set to memorize only one MAC address and shutdown the port if this violation occurs.
moses-switch# configure terminal
moses-switch(config)# ! grouping the range of ports, from 1 to 24
moses-switch(config)# int range gigabitEthernet0/1-24
moses-switch(config-if-range)# ! setting all of the ports to be access mode
moses-switch(config-if-range)# switchport mode access
moses-switch(config-if-range) # ! setting the maximum number of mac addresses allowed
moses-switch(config-if-range)# switchport port-security maximum 2
moses-switch(config-if-range) # ! saving the already existing MAC addresses for port security
moses-switch(config-if-range)# switchport port-security mac-address sticky
moses-switch(config-if-range)# ! setting the ports to shutdown if more than two MAC addresses is received
moses-switch(config-if-range)# switchport port-security violation shutdown
moses-switch(config-if-range)# ! Lastly starting up the service itself
moses-switch(config-if-range)# switchport port-security
Now please note that you can enable port security on a trunk, however regardless of the port it must be static, meaning that the switchport cannot be set to dynamic.
In addition, please note that while this example is shutting down the the port, in an enterprise environment it might be best to restrict or protect the port instead and set up an SNMP trap to alert an administrator of a potential problem. Also please note that this is just the tip of the iceberg, as port security can even rate limit and limit the number of MAC addresses saved for a VLAN.
The DNS service is vital part of any company's network and compromising it can lead to the loss of confidentiality and integrity. Therefore it is crucial service that needs to be both monitored and protected heavily.
In this post we are going to discuss 3 common DNS attacks that you should protect against, now given there are many more so continue to do your research afterwards. In addition, I am also going to assume that you understand how DNS works.
The basics of this attack is simple, redirect valid traffic going to a legitimate server over to a malicious one and it does this by corrupting the DNS cache data. Each time your computer encounters a domain name it does not recognize it must contact the DNS server, this server looks up the translation of IP addresses to domain names and then sends the packets accordingly. However, if an attacker can modify the information that the DNS server is telling users then it can affect entire companies, even more so, depending on the relationship this server has with others, then this false information can propagate to other servers in different organizations and so forth, eventually spreading like wildfire.
In short the attack can work like this:
DOS - TCP SYN Floods
In short, an attacker will overload the server by sending bogus SYN packets to abuse the TCP 3-way handshake connection. In reply, the server will send SYN-ACK responses, thus leaving the server 'hanging', which eventually leaves the server unable to connect to requests coming from valid users.
A method to prevent against such an attack would be to implement a host based firewall and a host-based intrusion detection system, while securing the network itself.
MITM - DNS Hijacking
Man in the middle DNS hijacking is the idea of an attacker intercepting and altering the cache data traffic between a user and the DNS server, thus leading the user to be redirected to a different destination that is often malicious.
While not fool-proof the three best methods that can be used to prevent against such an attack are to secure the surrounding network, locking down who is allowed access, using DNSSEC, and encouraging and sometimes even forcing clients to use HTTPS whenever browsing websites. Now, forcing users to use HTTPS will not encrypt the DNS traffic itself, but can act as a last line of defense with the web browser displaying that user has entered into an unsafe zone.
The first thing we must is download pfSense, after it has been installed, and setup we can login with the default username: admin and password: pfSense.
After going through the tutorial and setting everything up, it is recommended to change the DNS servers, now this is not a requirement,
Within this tutorial we are going to go over setting up a PfSense Firewall version 2.4, which can be downloaded here, and setting it up with Jumpcloud's Cloud LDAP authentication. Now these same steps can be used to setup with Window's servers as well with just a bit of tweaking. The first thing we must do is setup our Jumpcloud account, which is free for the first ten users! After you have activated your account and logged into the administrator's portal, we can create our first user.
Here, we can click on the plus sign under the Users tab to create our first user.
We can add all of the information for our new user, note that you can use the same email address that you created your administrative user with.
After saving our user, we can double click on the the name again to edit the details. Here, we have to check-mark the box "Enable as Admin/Sudo on all system associations" and "Enable as LDAP Bind DN". This will escalate the user's privileges and allow him/her to use Jumpcloud's LDAP login service.
Next, we can create the groups we want by clicking on the Groups tab on the far left and clicking the plus sign and from here we can add which users we want to which group. We can also assign specific permissions to the groups, however that is not needed in this tutorial.
Next, we we will move onto installing pfSense itself, after booting up the image for the first time we will be greeted with this message. Please press enter to accept.
After going through the basic installer, we will now be greeted with the black screen below. Next we have to setup the interfaces and the IP addresses for the interfaces. First we will want to enter in option 1. Now, normally we do not want to setup VLANs at this time, so you can press 'n' for that question. Next, select which interface you want for WAN and then for LAN. The next question will ask "Do you want to revert to HTTP as the webConfigurator protocol?" and it is advised to say 'no' unless for some reason the current network or browser will block HTTPS. After we have selected the interfaces, we now must set the IP addresses. Remember that WAN stands for Wide Area Network, so this means that anything facing externally of the network and the pfsense firewall web configuration can only be accessed internally. Now, my setup is different, as I am running everything within a virtual machine. Meaning that my home router is going to be assigning my IP address via WAN, however, my LAN will be vmnet8, with the pfsense firewall will act as the DHCP server. Therefore, this means that my setup is currently router to firewall to host, however you can have the pfSense placed outside of the router (or completely replace it) by copying the MAC address from the router and using DHCP for both IPv4 and IPv6 WAN. Also note that for most home networks, your IPv4 and IPv6 address can change at anytime, this is different for businesses however. Now, we will select option 2 and go through the process of which interfaces should be assigned statically or dynamically and if you want to setup a DHCP service on the LAN side.
After that, it is advised that you ping the firewall from a host that has received an IP address from the firewall. This will allow you to know if you have connectivity.
After this, we will need to make sure that we create a certificate for pfSense's use of Jumpcloud. We can create the certificate with the command:
echo -n | openssl s_client -connect ldap.jumpcloud.com:636 -prexit -showcerts | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'
If you want to save the certificate to the tmp folder we can edit the command a bit to follow this:
echo -n | openssl s_client -connect ldap.jumpcloud.com:636 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > /tmp/jumpcloud.chain.pem
Next, we can access the web portal from the LAN side, type in the IP address we set, mine is 172.16.84.1, and login with the username: admin and the password: pfsense.
After going through the initial setup, updating the firewall, and logging in with our new password, we can navigate to the Systems tab, Click on User Manager, then Groups, and create a new group by clicking on the green Add button. Here, we will name the group, please keep the name here as the same you created in Jumpcloud, as the two must sync. Next set up the Scope to Remote and click save. In order to assign permissions we have edit the group after it has been saved, and you can select which permissions you want then click save towards the bottom. After it will provide you with a confirmation page, please save again to update the changes.
Next, navigate to Authentication Servers and press the green Add button.
This is the below input, please edit for your own setup:
Descriptive name: JumpCloud
Hostname or IP Address: ldap.jumpcloud.com
Port Value: 636 (SSL)
Transport: SSL - Encrypted
Peer Certificate Authority: No Certificate Authorities defined.
Protocol Version: 3
Search Scope - Level: Entire Subtree
Search Scope - Base DN: ou=Users,o=ORG_ID,dc=jumpcloud,dc=com
Authentication Containers: ou=Users,o=ORG_ID,dc=jumpcloud,dc=com
Extended Query: &(objectClass=inetOrgPerson)(memberOf=CN=<group_name>,ou=Users,o=ORG_ID,dc=jumpcloud,dc=com)
Bind Credentials - User DN: uid=<username>,ou=Users,o=ORG_ID,dc=jumpcloud,dc=com
Bind Credentials - Password:<password>
User Naming Attribute: uid
Group Naming Attribute: cn
Group Member Attribute: memberOf
Group Object Class: groupOfNames
After all of that is done, click save and navigate to the Settings tab.
Next select JumpCloud under Authentication Server and click on "Save & Test", if all 3 report back as OK and the groups have been found, click the blue Save button.
We can verify that the user's groups and membership from Jumpcloud are syncing to pfSense by using the Diagnostics Authentication tool found under the Diagnostics/Authentication tab. From here, select the Authentication Server Jumpcloud and type in the user's details.
If you are able to login with the user then we know that Jumpcloud's LDAP authentication is working, play around with things to make sure that the permissions are synced up. However for the most part this project is complete!
Layer two, in accordance to the OSI model, is an innately insecure layer. We have to understand that within our networks, security is only as strong as our weakest link and if a layer is compromised since it is at the lower end, it may never be detectable, making layer two security crucial. Popular attacks that can arise on this layer are, VLAN Hopping, ARP spoofing, STP attacks, CAM table overflows, DHCP spoofing, and CDP/LLDP Reconnaissance. Here, we are going to examine what each attack is and certain counter measures you can take to prevent them.
1. VLAN Hopping:
Now, the goal of VLAN Hopping is to send traffic to a different VLAN from your own and we can accomplish this by one of two methods, switch spoofing or by double tagging. Switch spoofing is the idea of connecting to a switch within the network and setting up a trunk. Thus allowing the hacker to analyze the traffic and possibly alter it if the switch receives traffic from multiple VLANs. This attack takes advantage of the default enabled dynamic trunking. To prevent this, disabling dynamic trunking on all non-trunk ports should do the trick.
Double tagging however is a bit different. VLANs offer security by isolating traffic, this is done through tagging. However since tags can be nested, meaning that you can have a tag on-top of another tag, if the traffic being received by a switch has the tag of the native VLAN for that switch, then the switch will remove the outer tag and forward the traffic to the VLAN of the second tag, thus hopping a VLAN.
2. ARP Spoofing:
The goal of ARP Spoofing is to attempt to impersonate a computer within the same network. This can be done because ARP is an innately insecure protocol because it does not have a check operation. Therefore, if Bob's computer wants to communicate with Alice's and asks for her MAC address, but instead Susan replies, then all of the traffic sent from Bob that is supposed to go to Alice will instead be sent to Susan. You can counteract this by allowing Dynamic ARP Inspection, which verifies all ARP requests and responses sent across the network, segmenting out LANs to be as small as possible, and always keeping 802.1x in mind.
3. STP Attacks:
Spanning Tree Protocol is used to prevent loops within a network, thus making it an extremely crucial protocol. Because STP attempts to always find the best paths throughout the network, if an attacker, connects a device that triggers the optimization operation it can affect how traffic flows and can possibly re-route traffic through the newly connected switch. Due to the pause of STP, this can create a Denial of Service, greatly reducing the flow of traffic if repeated. You can counteract this by enabling Root Guard on the switches ports that should not become root ports and using BPDU Guard on all ports that have PortFast enabled.
4. CAM Table Overflows:
The CAM table is responsible for learning which MAC addresses are connected to which interfaces on the switch and sending the traffic in accordance to this table. This is a highly effective mechanism as the more addresses are learned the less broadcasts are needed, thus saving bandwidth. However each table can only be so large, therefore if this limit is reached, all traffic from unknown MAC addressed gets flooded throughout every interface. This leads to a Denial of Service as the switch, along with the network, eventually crawls to a halt. However, this can be counteracted by enabling Port Security to limit the number of MAC addresses that can be learned per-interface.
5. DHCP spoofing:
Similar to ARP spoofing, the goal of DHCP spoofing is to attempt to impersonate a computer. However in this case the computer is the DHCP server within the network. If the attacker connects a malicious DHCP server to the network, whenever a client requests an IP address the server that responds the fastest gets to assign the client an address and can control the gateway seen by that device. If the attack works perfectly, the hacker can re-route the traffic to his or herself and then send all of the traffic to the correct gateway, thus creating a MITM attack. The best way to counteract this attack is to use DHCP snooping, where you can configure ports to be either trusted on un-trusted.
6. CDP/LLDP Reconnaissance:
Link Layer Discovery Protocol and the Cisco propriety, Cisco Discovery Protocol, do essentially the same thing, they attempt to discover what type of device is connected to a particular port mainly for troubleshooting purposes. The issue however is that this information is available for anyone on the network, so if an attacker is able to listen in, he or she can gain this information as well. The best countermeasure is to simply disable the default enabled Cisco Discovery Protocol on your routers.
Nmap is one of the most important and versatile tools in any hacker's toolbox. It's powerful engine along with it's ease of use allows people who have no prior command line experience to pick it up fairly quickly. Personally, I have used nmap to help exploit systems but also to tell me what ports are open on a printer so I can access the web portal. Overall it is an extremely useful tool and below I am going to explain the 10 most useful Nmap commands you should learn.
At number 10: Traditional Scan (mostly checks to see if host is alive)
# nmap [IP address]
Example 9: A ping scan of the network:
# nmap -sP [network ID/subnet CIDR]
Number 8: SYN TCP port scan from ports 1 to 65535
# nmap -sS -p1-65535 [IP address]
Number 7: UDP port scan from ports 1 to 65535
# nmap -sU -p1-65535 [IP address]
Number 6: Skip the ping, scan specific ports for activity
# nmap -sn -p22,80,443 [IP address]
Number 5: OS detection with an aggressive scan
# nmap -O -A [IP address]
Number 4: Conducts an ACK TCP scan and attempts to find the versions of what is running on the ports
# nmap -sV -sA -p22,80,8080 [IP address]
Number 3: Spoofs the IP address on interface eth0, while fragmenting the packets, and conducting an ACK scan
# nmap -S [Spoof source IP address] -e eth0 -f -p20,21,22,2380,143,443,589,8080 -sA [IP address]
Number 2: Incorporating Nikto into your Nmap Scan
# nmap -p80,443 [IP address] -oG - | nikto -h -
Number 1: Nmap Scripting engine
# nmap --script-help=
Example script: http-brute, sshv1, smb-vuln-ms10-054,...
The nmap scripting engine is an incredibly useful tool, that I recommend everyone to learn.
Network administration is a complex field that requires an immense amount studying and dedication. Below are ten common entry-level interview questions. Now I must add that you should not memorize these questions, but instead should use them as a basis for your level of understanding. (Questions 5 through 7 may very depending on the job, but this is the general layout.)