January 12, 2017
After Part 1 which focused on setting up your network for IoT this post focus on making sure that the devices are the right ones and that they work in your network. The first can be accomplished by asking basic security questions and talking only with the more secure vendors further. In my experience that also leads to the better vendors which know IT and whom will make your life easier in the long run. There are plenty of vendors out there for whom the whole IT part is new as they are an old vendor in a given field which now needs to do the “network thing” and don’t have the employees for it. Johannes B. Ullrich at SANS ISC InfoSec came up with the idea to preselect IoT vendors with 5 questions. (You can read more on his reasoning behind each question in his post):
5 preselect questions
- For how long, after I purchase a device, should I expect security updates?
This time frame will show us how long we can plan to use the device in our network, as using devices which get no security updates will be a compliance violation in most companies.
- How will I learn about security updates?
Responsible vendors will add you to a security mailing list where you will get informed on all security related stuff via email.
- Can you share a pentest report for your device?
If the vendor cares at all at security he let an external expert make a pentest, which will at least find the worst and stupid security holes. If the vendor is able to show you such an report, you should really take that vendor in consideration.
- How can I report vulnerabilities?
We often found security holes in programs or devices and sometimes it is really hard to report that to the vendor in a way he accepts it and fixes the hole in a reasonable time frame. Sometimes we needed to go via our local Austrian CERT and sometimes that even was not enough as the vendor was in the US and only did something after their CERT asked them pointed questions. So a direct connection the guy(s) responsible for the security of device is important.
- If you use encryption, then disclose what algorithms you use and how it is implemented
If the vendor tells you something about “Proprietary” run away from the product! If you read that they use MD5 or RC4, the software on the device seems a little bit dated.
After selecting the best vendors ranked by the preselect questions you should make sure that the devices will run in your network. If you’re new to this kind of work you will not believe what garbage some vendors deliver. Some points are connected to your network and how it will look in the future.
- The device needs to support DHCP!
- Use DHCP reservations to provide fixed IP addresses
- Special case in a secure network is to disable ARP learning on the Layer 3 switches (makes MitM attack a lot harder). In this case DHCP is used for filling the ARP table.
- Check if the device will work with MAC oder 802.1x authentication flawlessly
- Some devices only send a packet if queried, which won’t work if the device got de-authenticated e.g. idle timeout or network problem. The device needs to send a packet ever so often so the switch sees the MAC address and can make a RADIUS request.
- The devices needs to support routing
- We had devices that where only able to talk within the subnet. In some cases we were not sure if the product really didn’t support it or just the technician was unable to configure it.
- As the PCs and servers need to be separated via a Firewall (see Part 1), this feature is a deal breaker
- It should be possible to configure a local NTP Server
- If not, the device time runs off or you need to allow the device to connect to the Internet, which can get complicated or insecure if you’ve different devices each using an other NTP server
- The devices needs to support automatic restart of services after power or network outage
- We had some devices which needed manual interventions to reconnect to the servers again after a network problem
- Embedding of external resources should be looked at. e.g. If a device needs jquery for its web GUI and lets the browser load that via jquery.org it will not work it your Internet is down. In some cases that does not matter, in some thats a deal breaker.
- support of 1Gbit Ethernet connection
- Sure I know that IoT devices do not need 1Gibt, but the devices will maybe run 10 years and you’ll have 10Gbit switches by than. It is not sure that 100Mbit will be supported or work flawlessly. e.g. Some current Broadcom 10Gbit chipsets don’t support 100Mbit half duplex anymore. You need an other chipset which is a little bit more expensive .. and you know what switch vendors will pick? 😉
So so far for part 2 of this series … the next part will be on some policy stuff you need to agree with department wanting that devices.
January 6, 2017
The last articles in this blog about IoT (often called Internet of Targets 😉 ) where about a specific cam or about IoT at home. This article series will be different, it will focus on the IoT in companies. Part one will talk about what you need to in order to prepare your network for IoT.
Prepare your network for IoT
There are 2 kinds of IoT devices/setups:
- ones that are directly connected to your network (e.g. house automation, access systems, …)
- ones that are connected via a mobile operator via GPRS, LTE, …. (e.g. car traffic counter, weather stations, webcam at remote places, …)
For the first ones it is a good idea to implement a separate virtual network, which means the traffic from and to the IoT devices always goes over a firewall before going to your servers or PCs. A normal company network should have following separate virtual networks outside the data centers.
- external Clients / visitors
- services = IoT
All those networks are connected to each other via a firewall and only required ports are opened. This separation is not arbitrary as it runs along some important differentiating factors:
- You’re PCs are normally centrally managed (monthly software updates, no administrator privileges for the users, …) and are allowed to access many and critical servers and services. Also there is normally no communication needed between 2 PCs, so you can block that to make an attacker the lateral movement harder/impossible.
- The VoIP phones need QoS and talk directly which each other, as only SIP runs to the server, the (S)RTP media streams run between the phones – peer to peer.
- Let’s face it, nobody installs software updates on their printers, but they are full computers often with Windows CE or Linux. So like IoT devices we need to contain them. Also one printer does not need to talk to an other printer – block printer to printer traffic.
So lets talk about the IoT network:
- Put the servers of IoT devices (if they are not fully cloud based) into you’re data centers in the proper DMZ.
- IoT normally don’t talk directly which each other as the don’t require that the different devices are in the same network at all. So I highly recommend to block client 2 client traffic also in the IoT network. This blocking is important as if an attacker got his hand on one device, he cannot exploit wholes in other IoT devices by simply leap frogging from the first.
After you got your internal IoT network set up we take a look at the devices you need to connect via a mobile operator. First it is never a good idea to put IoT devices directly onto the Internet. Sure you can can use a VPN router for each IoT device to connect back to your data centers, but there is an easier way if you’ve more than a few devices. Most mobile operators provide a service that contains following:
- separate APN (access point name in GSM/UMTS/LTE speech) which allows authorized SIM cards to connect to a private non Internet network
- you can choose the IP range of this special mad-for-you network
- Each SIM card gets assigned a fixed IP address in this network
- IPsec tunnel which connects the private network to you data center(s)
Here in Austria you pay a setup fee and monthly for the private network but the SIM cards and the cost for bandwidth are basically the same as for normal SIM cards which connect to the Internet. I recommend to choose 2 providers for this kind of setup as it will happen that one as a bad coverage at a given spot. With this network and the fixed IP addresses it is quite easy to configure the firewall securely.
The next part will take a look at the policy for implementing new IoT devices, on making sure that the devices are the right ones and that they work in your network.
November 18, 2016
If you know Mikrotik Routers you know that you’re able to access them via MAC Telnet (see here for more details) via Layer2 with Winbox. But running Winbox via Wine on a Linux is not that great for using MAC Telnet, and there is a better way .. just use MAC-Telnet from Håkon Nessjøen. On Ubuntu/Debian you can just install the package with
sudo apt-get install mactelnet-client
and you see its feature like this:
$ mactelnet -h
Usage: mactelnet <MAC|identity> [-h] [-n] [-a <path>] [-A] [-t <timeout>] [-u <user>] [-p <password>] [-U <user>] | -l [-B] [-t <timeout>]
MAC MAC-Address of the RouterOS/mactelnetd device. Use mndp to
identity The identity/name of your destination device. Uses
MNDP protocol to find it.
-l List/Search for routers nearby (MNDP). You may use -t to set timeout.
-B Batch mode. Use computer readable output (CSV), for use with -l.
-n Do not use broadcast packets. Less insecure but requires
-a <path> Use specified path instead of the default: ~/.mactelnet for autologin config file.
-A Disable autologin feature.
-t <timeout> Amount of seconds to wait for a response on each interface.
-u <user> Specify username on command line.
-p <password> Specify password on command line.
-U <user> Drop privileges to this user. Used in conjunction with -n
-q Quiet mode.
-h This help.
So lets give it a try, first with searching for my home router
$ mactelnet -l
Searching for MikroTik routers... Abort with CTRL+C.
IP MAC-Address Identity (platform version hardware) uptime
10.x.x.x 0:xx:xx:xx:xx:xx jumpgate (MikroTik x.x.x. xxxx) up 139 days 5 hours XXXXX-XXXX vlanInternal
and then we’ll connect
$ mactelnet 0:xx:xx:xx:xx:xx
and we’re connected.
November 14, 2016
I’ve some info for you, if you’re running Mikrotik RouterOS in a version below 6.34rc45 and are using a tunnel (like IPIP over IPsec). If you don’t boot the router for about 248 days, your router will get inaccessible. This is specially bad if your routers are in remote locations and you’ve got multiple routers with the same updates ( like > 100 😉 ) as you did the firmware update at the same time.
The changelog for the 6.34rc45 version states the problem, but it doesn’t tell you that the router is offline and can only be accessed via serial cable.
*) tunnel – fix complaining about loop after ~248 days;
If you look into the log via the serial port you’ll see
07:21:13 interface,info tunnel_1 link down
07:21:13 interface,info tunnel_2 link down
07:21:13 interface,info tunnel_3 link down
07:21:13 interface,info tunnel_4 link down
07:21:14 interface,warning tunnel_1 transmit loop detected, downing interface for 60 seconds
07:21:14 interface,warning tunnel_2 transmit loop detected, downing interface for 60 seconds
07:21:14 interface,warning tunnel_3 transmit loop detected, downing interface for 60 seconds
07:21:14 interface,warning tunnel_4 transmit loop detected, downing interface for 60 seconds
and nothing else. 😉
If you’re running an affected version you need to reboot before reaching 35 weeks or upgrade to a new version.
October 2, 2016
You ask why you should need this at all? Easy, sometimes a tcpdump is not enough or not that easy to use:
- You want to check the TTL/hop count of BGP packets before activating TTL security
- You want to look at encrypted SNMPv3 packets (Wireshark is able to decrypt it, if provided the password)
- You want to look at DHCP packets and their content
Sure, it’s quite easy to sniffer on a remote Linux box with tcpdump into an file and copy that that over via scp to the local system and take a closer look at the traffic. But getting used to the feature of my Mikrotik routers to stream traffic live to my local Wireshark, I thought something similar must also be possible with normal Linux boxes. And sure it is.
We just use ssh to pipe the captured traffic through to the local Wireshark. Sure this is not the perfect method for GBytes of traffic but often you just need a few packets to check something or monitor some low volume traffic. Anyway first we need to make sure that Wireshark is able to execute the dumpcap command with our current user. So we need to check the permissions
-rwxr-xr-- 1 root wireshark 88272 Apr 8 11:53 /usr/bin/dumpcap*
So on Ubuntu/Debian we need to add ourself to the wireshark group and check that it got applied with the
id command (You need to logoff or start a new sesson with
su - $user beforehand). Now you can simply call:
ssh [email protected] 'tcpdump -f -i eth0 -w - not port 22' | wireshark -k -i -
And now the really cool part comes. I’m using Ubiqity Unifi access points in multiple setups and I sometimes need to look at the traffic a station communicates with the access point on the wireless interface. With that commands I’m able to ssh into the access point and look at the live traffic of an access point and a station which is hundreds of kilometres way. You can ssh into the AP with your normal web GUI user (if not configured differently) and the bridge config looks like this
BZ.v3.7.8# brctl show
bridge name bridge id STP enabled interfaces
br0 ffff.00272250d9cf no ath0
You can choose one of that interfaces (or the bridge) for normal IP traffic or go one level deeper with wifi0, which looks like this
ssh [email protected] 'tcpdump -f -i wifi0 -w -' | wireshark -k -i -
That’s cool!?! 😉
September 17, 2016
It is good practice to configure an individual MD5 password for each BGP peer, but this is not enough. Why?
- Resource consumption attacks against TCP connections protected with MD5 as the router must verify the MD5 signature of packets it receives
- Many routers are based on Linux as there base operating system and there is a weakness which allows an attacker to insert arbitrary data into TCP connection. For more details click on this link.
The classical BGP TTL security is based on using a low TTL, generally 1, for single-hop BGP connections. The measure is effective in preventing a BGP connection from being established from a peer more than one hop away. Why? routers decrement the TTL when routing the packets and won’t route packets with a TTL of 1. So if your BGP session is a multi hop connection over one router a TTL of 2 makes sure the packet travels only over one router and not more. That sounds fine but has still has a drawback, as packets with a TTL of 1 are trivial to spoof, so rogue packets will still reach the router – leading to the problems described above.
GTSM (Global TTL Security Mechanism; RFC 5082, which obsolated RFC 3682) suggests the opposite approach. Instead of using a TTL value of 1, it suggests a value of 255 and discarding any packets received with have a TTL lower than 255 minus the hop count for this BGP session. Doing that an attacker is not able to perform the attack as the TTL gets decremented by every router (something the attacker can’t prevent). So setting the TTL on the router to 255 and having no multi hop BGP session allows to drop all packets on the receiving router which are lower than 255. This way only an attack in the same subnet is possible.
After the theory here the actual doing:
For Cisco routers is quite easy, just add
ttl-security hops 1 (for a BGP session in the local subnet) to the peering config
neighbor x.x.x.x command. For Mikrotik routers it is a little more complicated. For IPv4 connections configure following (should be default anyway):
/routing bgp peer set 0 ttl=255
For dropping incoming packets just use the firewall on the Mikrotik with a command like this:
/ip firewall filter add action=drop chain=input log=yes log-prefix="RFC 5082 block" src-address=xxx.xxx.xxx.xxx ttl=less-than:255
For IPv6 it is a little more complicated as setting the TTL for bgp peer configuration does have no effect (I’ve reported the bug already) but there is a simple workaround possible. Just use the mangle function of the firewall to set the correct hop count:
/ipv6 firewall mangle add action=change-hop-limit chain=output dst-address=xxx:xxx:xxx::xxx/128 new-hop-limit=set:255
Now you need only to filter the IPv6 packets:
/ipv6 firewall filter add action=drop chain=input log=yes log-prefix="RFC 5082 block" src-address=xxx:xxx:xxx::xxx/128 hop-limit=less-than:248
This configuration is quite easy and minimal invasive but should help a lot against attacks on your BGP routers.
July 2, 2016
I’ll keep reading about the whole Internet of Things (IoT) but something I see missing is the security aspect. Sure there are white papers and article out there how an enterprise should deploy IoT in a secure way, but not much for home and SOHO networks. In this blog post I’ll address the problems of current IoT devices and what you can do to mitigate them. I’ll concentrate on typical IoT devices used/designed for home users.
Why the security of IoT devices sucks
Just remember one mantra – IoT devices suck at security – and here is the why.
- Many of these devices are build by Start-ups, which have one goal. Get the product out as fast as possible and get the company bought by someone and hit pay day. Even if not, they need to get enough revenue first and to start than fixing the security problems.
- If the device is not build by a Start-up than it got build by an established manufacturer in the area the IoT device is build for. The problem is the manufacturer has no idea about connected devices and that Internet stuff – Its called “Neuland” :-). They will make every error the IT industry did 10-15 years ago. Yes, if you’re that long in the business as I’m you’ll see the same security holes you saw in the first years of this millennium for normal PCs now for IoT devices.
- Usability and security is not easy .. so most of the time the easy to use and insecure variant is used
- If the IoT device is for a semi established area like IP cams / baby cams the devices are build and designed by a Chinese company and sold under various labels. The company selling the devices does not know anything about the internal workings. If a security problem is found and somehow the OEM vendor in China fixes the problem, you’ll wont get an update from the company that sold the devices.
- Automatic updates of the devices is not the norm, so most devices wont get any updates. While in the PC marked it is for years now common that software get updates automatically, the same is not true for most IoT devices. And lets be honest who is checking for security updates of the light bulbs on a regular base?
- But before we can talk about automatic updates lets don’t forget that for most IoT devices you’ll get updates only for a short period of time. The vendor wants to sell his next product, so why support the old one? To make the problem bigger most IoT will get used longer than a typical mobile phone, which also suck at security update time frames. No one will replace his/her IP cam every 2 years like a mobile phone (ok, that’s also not true, but its typical a shorter interval)
- UPNP was a bad idea and still is one. Some IoT automatically open ports from the internet so any security flaw can be exploited directly from anywhere in the world. Oh, joy! 🙂
- Even if the device does not use UPNP it often connects per default directly to a cloud service, over which you (and potentially an attacker) can access your device. e.g. accessing the baby cam via the mobile phone app via and cloud service. There have been some horrible security flaws in the past, like a consecutively numbered ID without password or the MAC address of the device as ID (really heard the guess an MAC address if you know the vendor ID 😉 ).
There are some more points I could made, but these should be already depressing enough.
ps: yes, there are some IoT devices with good security but these are less than 5% of the total market.
Theoretical mitigating the problems
As we’ve established that the security is not good, we need ways to mitigate the problem, within the scope of a home network. To be honest that can’t be done by your typical mum, but needs some one technical minded – but others would not read my blog anyway.
Securing or hardening IoT devices is sometimes possible but for most consumer ones that won’t work. So lets accept that the device will have security problems. In some cases that will be a big problem in its own right, e.g. a IP cam that can be watched from anyone world wide. In other cases e.g. a light bulb that can be controlled from anyone world wide is more a nuisance that a real problem. The same is true for weather station that is readable world wide.
For the first case there is nothing that can be done on the network level as general rule, as disabling the Internet connection for the device will prevent it from working in the first place. Sure there are cases where the cloud connection is not needed, in these you can deactivate or block it. But for the second case there is something. Let’s assume the attacker got access to the IoT device, which is by itself in this example case not that bad, surely a nuisance but not a big problem. The problem arises now from the fact that the IoT device is controlled by the attacker and what he can do with that. So lets look at some possible scenarios.
- If the device is connected via WiFi the attacker has now the WPA2 PSK key from your WiFi.
- If the family NAS provides the shares without username/password an attacker can access it
- Maybe the router can be configured without a secure password or has also a weakness. The attacker can use this to change the DNS servers to allow MiTM attacks
- ARP spoofing and similar attack are also possible.
To guard against that attacks you need to segment the IoT network from your normal network, even better isolate the various IoT devices from each other.
Practical mitigation – three stupid routers
The segmentation can be achieved in various ways. The first one needs only standard routers …. just more than one … you need 3 routers. Lets take a look at the diagram:
The first router is often provided by the cable or telephone company and you need to buy 2 stupid/cheap routers behind it. One is for the normal internal network and one for the IoT devices that connect a cloud service. For the IoT device router configure the WiFi in client isolation mode (if possible). As both (internal and IoT) routers masquerade their clients a direct connection is not possible. If a connection should be possible a port forwarding needs to be enabled and also make sure that the IP subnets are different. If one IoT devices gets compromised it can not leak the internal WiFi password as it does not have it. Also accessing the NAS is not possible as the ARP spoofing is not possible. Use the provider router for guest which should not be able to get anything except Internet.
The setup is quite simple and also cheap but has its short comings:
- Works only for apartments and small houses – if you need more than one access point for you’re house it does not work.
- You need multiple routers, which need more power.
- You lack flexibility
Practical mitigation – intelligent router / access points
If you move away from the typical stupid routers you can make use of the more advanced features. The exact setup depends on the used network devices, so I’ll can only show a possible setup. Following requirements need to be met by scenario setup.
- Three floors, each with its own access point
- IoT and internal devices in each flow, cable and wireless connect ones (multiple SSIDs on each access point)
- Clients want to move within the building without loosing connection (same SSIDs on all access points)
Just to make it clear, there are other setups possible to fulfill the requirements. Following diagram shows the possible setup.
The router or firewall (could be a router like a Mikrotik or a pfSense firewall) is the gateway for all 3 networks (yes, I through a guest network in for good measure 🙂 ). On it the policy which network is allowed to connect to which other network is configured. All three networks are connected to the managed switch (if the router has enough ports it may can fulfill the role of switch too). On the switch most ports will be configured for one VLAN but the ports to the access points get all three VLANs.
The access points get configured in way that the management IP address is in the internal VLAN and a separate SSID is used for each VLAN. All access points use the same SSID for the same VLAN, so roaming for the clients is possible. Set the SSID for IoT and external use to client isolation mode (one wireless client can’t communicate with an other)
Optional, if the the switch supports it. Configure private VLANs for the IoT and external network, so only the router can talk with all devices
I hope this blog post shows you the basics for readying your home or maybe SOHO network for IoT devices which will surely come.
April 29, 2016
Today I’ll write a completely different security blog post to which I normally write. This one is about KNX – I’ll guess most readers (which are largely IT people) don’t even know what it is about. Here from Wikipedia:
KNX is a standardized (EN 50090, ISO/IEC 14543), OSI-based network communications protocol for building automation. KNX is the successor to, and convergence of, three previous standards: the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus (EIB or Instabus). The KNX standard is administered by the KNX Association.
Now you’re asking why I’m writing about it and why I wrote it’s a security blog post? The KNX standard is now getting whitely deployed in Tirol in new office buildings and even is used on bigger renovations of these. Most of these deployments are done by civil and electrical engineer, which don’t think (care?) about IT security. And as it is a network communication protocol and is often connected to the IT network of the company someone in the company should think about it.
So let’s starts with the basics. The most common form of deploying that network (called KNXnet sometimes only KNX) is over a two wire bus (twisted pair, called KNXnet TP) which is routed in parallel to the 230 V electrical power supply KNXnet connects all devices and systems of the building. To make the list complete following media are possible:
- TP: twisted pair
- PL: power line (over the normal 230V lines)
- IP: Internet protocol
- RF: wireless
The network speed is 9600 bit/s and following device groups get normally connected to the network:
- Sensors (e.g. push buttons, wind-, temperature-, movement-sensors)
- Actuators (dimming units, electrical heating valves, displays)
- System devices and components (e.g. Line-Couplers, Backbone-Couplers)
Most often the system is used to automate the building (turn all lights of if no one is in the building, move the blinds up and down), but there are also implementations which are more in the direction of alarm systems. In a security respect that means that everywhere any device, which is connected to KNX networks, is located (outside?) an attacker can get access to the network. In any case if the system/building is larger the building manager would like to configure the system via his working PC, which leads to a connection to the IT network. This a common case so the “The KNX standard – the basics” shows following diagram:
But lets keep looking at the KNXnet more directly. Setting up the KNX network is possible via 3 bus topologies:
These topologies can be mixed as needed, but no ring is not allowed. As the line and star topology are a subset of the tree topology, the tree topology is the most flexible one and used in most bigger installations. The network IDs of a given nodes is based on its location in the tree (and looks like that 1.5.1), more information can be found here. Following diagram from the “The KNX standard – the basics” shows a full network over various media. The white boxes are the networks IDs of the various devices connected.
building automation security
As we now know how the system works in basic lets take an overview look why building automation sucks at security.
- Default passwords: Yes, you’ll see building automations systems in the wild with default passwords. If set a different one it won’t comply to the password policy of the company.
- No authentication: Be it for users or devices
- No encryption
- Management system reachable from the Internet (e.g. for easier support from the vendor)
- Back door access: Some vendors deploy UMTS/LTE routers and connect via them to the system. This is often done if the system has problems in the first years of the deployment. e.g. most often seen for heading systems … a high percentage seems to have problems in the first years)
- No separation from the normal PC IT network
And these points are mainly because the building automation is not part of / controlled by the company IT department and therefore not on the radar of the IT security staff.
KNX specific problems
So now lets look at some KNX design problems. KNX providers filters on the line couplers to limit the load on the network. These provide a feature like TTL the field in the IPv4 packets do. But if you use a routing counter of 7, that goes through every filter. This allows to send packets from a subsidiary line (does not matter where you’re connected to the network) to the complete network. You just need to capture a packet (or guess one) which tells all lights to turn off (to show something harmless ;-)) and resend it at a later time with a routing counter of 7 to turn every light in the building of. Spoofing of the network id is simple, just choose one … good luck finding the place where the bad device is – it could be anywhere in (or even outside) the building and it can completely control it. Take a look at following sides from a presentations at BSidesVienna 2014 to get to know many more problems, like code injection to the ETS software and so on. So attacking the IT network over it is also possible .. maybe the ETS software runs in the same networks as you’re other servers? Its really broken from a security stand point.
Hint: KNX for hotels is also quite common and every guest room has access to the KNX network. Just saying – don’t do it 😉
Hint 2: If someone tells KNX provides security features like a password. Reply: Yes – sure …. it’s optional and its a 4 (in words “four”) byte password transmitted in clear text … really hard to sniff or guess ;-).
Following software can be used to play with KNXnetworks
If you’re in an IT security roll at the IT department you most likely cannot circumvent the installation of a KNX bus, but make sure that the system does not allow any attack vector against your services and systems. Think about it like an external IT network, you need to protect your systems against it (e.g. Firewall, network separation, …) . Make the normal security checks of the devices directly connected to your network (nmap, openvas scans, check used passwords, software versions, ….) and make sure that its clear (in writing 😉 ) who is responsible for maintaining the KNX network it’s security – its not your.
If you’re a building manager … talk and listen to the security guys from your IT department. They fight every day against attacks and know how to mitigate security problems.
March 14, 2016
In my last blog post I wrote about blocking, detecting and mitigating the Locky Ransomware. I’ve referenced to a earlier blog post of mine which allows to block traffic to/from the Tor network. This blog post combines both – a way to block Ransomware botnet C&C traffic on a Mikrotik router. The base are the block lists from Abuse.ch, which also provide a nice statistic. Locky is not the most common Ransomware today.
You need also a small Linux/Unix server to help. This server needs to be trustworthy one as the router executes a script this server generates. This is required as RouterOS is only able to parse text files up to 4096 by itself, and the IP address and domain list is longer.
So first we create the script
/usr/local/sbin/generateMalwareBlockScripts.py on the Linux server by downloading following Python script. Open the file and change the paths to your liking. The filename path works on CentOS, on Ubuntu you need to remove the
html directory. Now make the file executable
chmod 755 /usr/local/sbin/generateMalwareBlockScripts.py
and execute it
No output is good. Make sure that the file is reachable via HTTP (e.g. install httpd on CentOS) from the router. If everything works make sure that the script is called once every hour to update the list. e.g. place a symlink in
ln -s /usr/local/sbin/generateMalwareBlockScripts.py /etc/cron.hourly/generateMalwareBlockScripts.py
Copy and paste following to get the IP address script onto the router:
add name=scriptUpdateMalwareIPs owner=admin policy=ftp,reboot,read,write,policy,test,password,sniff,sensitive source="# Script which will download a script which adds the malware IP addresses to an address-list\
\n# Using a script to add this is required as RouterOS can only parse 4096 byte files, and the list is longer\
\n# Written by Robert Penz <[email protected]> \
\n# Released under GPL version 3\
\n# get the \"add script\"\
\n/tool fetch url=\"http://10.xxx.xxx.xxx/addMalwareIPs.rsc\" mode=http\
\n:log info \"Downloaded addMalwareIPs.rsc\"\
\n# remove the old entries\
\n/ip firewall address-list remove [/ip firewall address-list find list=addressListMalware]\
\n# import the new entries\
\n:log info \"Removed old IP addresses and added new ones\"\
and copy and paste following for the DNS filtering script – surely you can combine them … I let them separated as maybe someone needs only one part:
add name=scriptUpdateMalwareDomains owner=admin policy=ftp,reboot,read,write,policy,test,password,sniff,sensitive source="# Script which will download a script which adds the malware domains as static DNS entry\
\n# Using a script to add this is required as RouterOS can only parse 4096 byte files, and the list is longer\
\n# Written by Robert Penz <[email protected]> \
\n# Released under GPL version 3\
\n# get the \"add script\"\
\n/tool fetch url=\"http://10.xxx.xxx.xxx/addMalwareDomains.rsc\" mode=http\
\n:log info \"Downloaded addMalwareDomains.rsc\"\
\n# remove the old entries\
\n/ip dns static remove [/ip dns static find comment~\"addMalwareDomains\"]\
\n# import the new entries\
\n:log info \"Removed old domains and added new ones\"\
To make the first try run use following command
/system script run scriptUpdateMalwareIPs
/system script run scriptUpdateMalwareDomains
if you didn’t get an error
/ip firewall address-list print
/ip dns static print
should show many entries. Now you only need to run the script once a hour which following command does:
/system scheduler add interval=1h name=schedulerUpdateMalwareIPs on-event=scriptUpdateMalwareIPs start-date=nov/30/2014 start-time=00:05:00
/system scheduler add interval=1h name=schedulerUpdateMalwareDomains on-event=scriptUpdateMalwareDomains start-date=nov/30/2014 start-time=00:10:00
You can use the address list and DNS blacklist now in various ways .. the simplest is following
/ip firewall filter
add chain=forward comment="just the answer packets --> pass" connection-state=established
add chain=forward comment="just the answer packets --> pass" connection-state=related
add action=reject chain=forward comment="no Traffic to malware IP addresses" dst-address-list=addressListMalware log=yes log-prefix=malwareIP out-interface=pppoeDslInternet
add action=reject chain=forward comment="report Traffic to DNS fake IP address" dst-address=10.255.255.255 log=yes log-prefix=malwareDNS out-interface=pppoeDslInternet
add chain=forward comment="everything from internal is ok --> pass" in-interface=InternalInterface
If a clients generates traffic to such DNS names or IP address you’ll get following in your log (and the traffic gets blocked):
20:07:16 firewall,info malwareIP forward: in:xxx out:pppoeDslInternet, src-mac xx:xx:xx:xx:xx:xx, proto ICMP (type 8, code 0), 10.xxx.xxx.xxx->104.xxx.xxx.xxx, len 84
20:09:34 firewall,info malwareDNS forward: in:xxx out:pppoeDslInternet, src-mac xx:xx:xx:xx:xx:xx, proto ICMP (type 8, code 0), 10.xxx.xxx.xxx ->10.255.255.255, len 84
ps: The Python script is done in a way that it easily allows you to add also other block lists … e.g. I added the Feodo blocklist from Abuse.ch.
February 4, 2016
This the last part of the the series “tips on how to provide a secure public WiFi hotspot”. In the first two parts we concentrated on the wireless and layer 2 and 3 part, this time we take a look at the application layer stuff you should tune to provide a secure hotspot.
Captive Portal and non HTTP traffic
If you want or need to show the user a website before he is able to surf the web, you should not only think about redirecting HTTP to your landing page. You should reject (send an ICMP error) for all other TCP connection attempts. Why? Many pages are nowadays HTTPS and letting the user wait for a time-out is not nice. Sure technical minded user will not wait, but others may do. Sure this is not a security advice but an usability one. But it does work nice together with following: Don’t try to provide your own TLS certificate to redirect traffic to the captive portal. Users should not be trained to accept error messages and ignore them and it will give your hotspot an bad look security-wise.
There is just nothing you can do to redirect HTTPS URLs. Just make sure that the captive portal detection of modern operating systems work and so the user is told there is a captive portal.
HTTPS for captive portal
If you require any data from the user except accepting the terms of service your captive portal should be HTTPS. Get an official DNS name for your portal, e.g. portal.<company>.com and a valid TLS certificate. As there are multiple methods for getting free TLS certificate e.g. startssl or let’s encryt, you should get a real one. One thing that is important to whitelist for your captive portal are the OCSP and CRL URLs of your certificate, issuing CA and root CA. To check for the URLs look at the certificate details for all certificates in the chain of your captive portal. Following images show the 2 places for google.com (you need to check also the Google Internet Authority G2 and GeoTrust Gobal CA in this case.)
Why, you ask, you should whitelist these URLs? The browsers will check them before showing your captive portal site. Some/Most browsers will fail open, but some will fail close.
Limit and monitor the DNS
If the user has not past the captive portal his only way though the firewall will be the DNS server. You normally need to resolve the requests to the true IP address to guard against problems with false cached DNS entries after the user past the captive portal. As the user is able to craft the requests as he likes it is possible to send data through to a 3rd party DNS server. This setup can be used as DNS tunnel – it will be not fast but its possible to work through it. As nowadays simple howtos like following and OpenSource tools are provided, consider it easily possible for most power users – its not a expert thing any more.
So now comes the question what you can do against it. In this case you don’t need to block the covert channel of sophisticated malware but just script kiddies that want to tunnel through. Your typical user will only need A and AAAA query types. Tunneling is mostly done via TXT as it allows big packets. Following query types are common:
Content Filtering via DNS
Often you’re required to filter certain traffic but don’t want to setup and maintain a transparent proxy or with all the HTTPS it does not help that much any more. An easy way is to use the OpenDNS system, which allows to select certain categories which are then blocked on the DNS level (Query will resolve to an error page) . If you redirect all port 53 traffic to your DNS server which uses the OpenDNS ones as recursive DNS servers you should be good for most cases.
Just reject (blocking lets the client run into timeouts) TCP port 25, otherwise infected client systems will flood your bandwidth with SPAM mails. A mail agent should not send mails to the mail server via port 25 anyway.
I hope this article series helped you and leads to more secure hot spots I’m also able to enjoy. 😉