Thursday, July 30, 2015

Saving Polar Bears When Banner Grabbing

By Vincent Berg @santaragolabs

As most of us know, the Earth’s CO2 levels keep rising, which directly contributes to the melting of our pale blue dot’s icecaps. This is slowly but surely making it harder for our beloved polar bears to keep on living. So, it’s time for us information security professionals to help do our part. As we all know, every packet traveling over the Internet is processed by power hungry CPUs. By simply sending fewer packets, we can consume less electricity while still get our banner grabbing, and subsequently our work, done.

But first a little bit of history. Back in the old days, port scanners were very simple. Some of the first scanners out there were probe_tcp_ports (published in Phrack #46) and pscan.c by pluvius. The first scanner I found that actually managed to use non-blocking I/O was strobe written by Proff, more commonly known nowadays as Julian Assange, somewhere in 1995. Using non-blocking I/O obviously made it a lot faster.

In 1996, scantcp.c written by Uriel Maimon (published in Phrack #49) became one of the first scanners to use half-open/SYN scanning. This was followed by the introduction of nmap by Fyodor Lyon in The Art of Port Scanning (published in Phrack #51) in 1997.

Of course, any security person worth his salt knows nmap and is at least familiar with a good subset of the myriad of scanning techniques it implements. But, in many cases, when scanning for TCP ports we want results as quickly as possible, so we can get a list of open ports we can connect to from the source address that we’re scanning and subsequently identify the services behind those ports.

To determine if a port is open, we sent out a SYN packet and watch for one of several things to happen. Assuming there are no firewalls or routing issues, the receiving TCP/IP stack will either:
  •  Send a packet with the RST flag set, which means the port is closed and the host is not accepting connections on that port.
  • Send a packet with the SYN and ACK flags set, which means the host is accepting the connection. The Operating System under which nmap runs doesn’t know anything about the outgoing SYN packet (as it was created in raw mode), and subsequently it will send back an RST packet as a reply.

To summarize see the following image from (courtesy of the nmap book)

This is great, as we can now list the open ports, and this forms the basis of half-open/SYN scanning. However, one thing that nmap does is track the number of outstanding probes and retransmit them a number of times if no response is received in a timely fashion. This leads to a lot of complexity, and it makes scanning slower too. Besides that, standard scanning modes do not offer protection against an adversary who is feeding wrong responses down the pipe. So nmap can, under such circumstances, claim that a port is open when it is not, or vice versa.

This lead to some efforts to protect the outgoing SYN probes by cryptographically signing them. The first known public release of this was scanrand by Dan Kaminsky introduced in his collection of Paketto Kereitsu utilities. It generates and fires off packets as quickly as possible. Each SYN probe is protected by a cryptographic cookie based on an HMAC calculated over the 4-tuple identifying the connection (the source and destination IP addresses and ports) and a randomly generated secret. As a valid reply for an open port needs to be sent back with an incremented TCP ACK value, it’s easy to recalculate the original cookie and deduce if it was indeed a response to a packet sent out by the scanner. This completely eliminates the need to keep state, although a bit of packet loss can mean some probes may get lost and won’t be retransmitted, and as such not all open ports will be discovered.

So that’s all great. But what’s one of the first things we do after discovering an open port? Connect to it properly. Possibly to do a banner grab or a version scan or just to see what the heck is behind this port. Now when it comes to standard IANA port assignments, in most cases, it’s relatively clear what’s behind a port. If open, port 22 is most likely SSH, port 80 HTTP, port 143 IMAP etc. But we still want to check.

So what happens if you do an nmap version scan? Or a simple banner grab after a port scan? After receiving a SYN|ACK reply from an open port, the scanner jots down that the port is open, and then connects to it. The only way to do this is to go through libc and the kernel and do a full TCP connect() call. This will result in another SYN - SYN|ACK - ACK exchange on the wire before any data can actually be exchanged. Combining that with the original SYN - SYN|ACK - RST exchange, that’s a total of three potentially unnecessary packets being exchanged.

So how would one go about solving this? There are a few approaches. One is by patching the host kernel and enabling an API that allows us to send out raw SYN probes without keeping any state. By then adding a callback API when valid SYN|ACK packets are received, we would have a mechanism to turn these connections into valid file descriptors. But that means writing a lot of complicated kernel code.

The other approach is to use a userland TCP/IP stack. These work exactly the same as any normal TCP/IP stack, but they just run in userspace. That makes it easier to integrate them into scanners and modify them without having to deal with complicated custom kernel modules.

As I wrote several scanners over the years, I always wanted to have a good userland TCP/IP stack, but I never saw one that fit my needs or whose code quality I actually liked. And writing one myself seemed like a lot of work, so I shied away from it.

Anyhow, ever seen the movie American Beauty? Where Kevin Spacey’s wife comes home and asks him about the 1970 Pontiac Firebird out on the driveway which he bought with the money received from blackmailing his former boss? It’s such a great scene; “the car I’ve always wanted and now I have it. I rule”.

That’s sort of how I felt when I stumbled over Patrick Kelsey’s libuinet. The userland TCP/IP stack I’ve always wanted and now I have it. I rule!! It’s a port of the FreeBSD TCP/IP stack with kernel paradigms ported back on userland libraries, such as POSIX threads. It’s great, and with a bit of fiddling, I got it to work on Linux too.

That enabled me to combine the two ideas into just one port scanner; the stateless SYN scanning first introduced in scanrand and the custom TCP/IP stack. Now I can immediately resume doing a banner grab or sending a request without having to do another TCP connect() call. To prevent the hosting Linux kernel from interfering and sending a RST packet, an iptables firewall rule will be inserted. Otherwise, the userland TCP/IP stack will try to pick up the connection from the SYN|ACK but then the Linux kernel has already frontran it and will have sent the RST out. After this was figured out, tying everything else together in the tool was relatively easy, thus, polarbearscan was born.

The above approach saves us from sending a couple of packets. And thus saves CPU cycles. And so we can hopefully give the polar bears a few more years. The code for the polarbear scanner can be found here, and instructions on how to compile it and get it up and running on Linux systems are inside in the README in the distribution.

A sample run of the tool doing a standard banner grab for port 21, 22, 143 (FTP, SSH, IMAP) with a bandwidth limitation for outgoing SYN probes of just 10kbps and scanning a /20 range will yield something like this:

$ sudo ./pbscan -10k –sB –p21,22,143 x.x.x.x/20

seed: 0xb21f7f4e, iface: eth0, src: (id: 54321, ttl: 64, win: 65535)

x.x.x.6:21 -> 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
x.x.x.6:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.14:21 (t/o: 0s)
x.x.x.15:21 (t/o: 0s)
x.x.x.16:21 (t/o: 0s)
x.x.x.8:22 -> SSH-2.0-OpenSSH_5.3
x.x.x.8:21 -> 220 ProFTPD 1.3.3e Server ready.
x.x.x.10:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.10:21 -> 220 ProFTPD 1.3.5 Server ready.
x.x.x.9:22 -> SSH-2.0-OpenSSH_5.3
x.x.x.9:21 -> 220 ProFTPD 1.3.3e Server ready.
x.x.x.17:21 (t/o: 0s)
x.x.x.11:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.7:21 -> 220 Core FTP Server Version 1.2, build 369 Registered
x.x.x.11:21 -> 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
x.x.x.13:21 -> 220 ProFTPD 1.3.4d Server ready.
x.x.x.13:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.14:22 -> SSH-2.0-OpenSSH_5.1p1 Debian-6ubuntu2
x.x.x.15:22 -> SSH-2.0-OpenSSH_5.1p1 Debian-6ubuntu2
x.x.x.16:22 -> SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2
x.x.x.18:22 -> SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze5
x.x.x.19:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.19:21 -> 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
x.x.x.21:22 -> SSH-2.0-OpenSSH_5.3
x.x.x.22:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.25:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.26:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.27:22 -> SSH-2.0-OpenSSH_4.3
x.x.x.36:22 -> SSH-2.0-OpenSSH_5.3
x.x.x.38:22 -> SSH-2.0-OpenSSH_6.6p1 Ubuntu-2ubuntu1
x.x.x.40:22 -> SSH-2.0-OpenSSH_4.7p1 Debian-8ubuntu1.2
x.x.x.17:22 (t/o: 5s)
x.x.x.35:22 (t/o: 5s)
x.x.x.37:22 (t/o: 5s)
x.x.x.239:22 -> SSH-2.0-OpenSSH_5.1p1 Debian-5
x.x.x.100:22 (t/o: 5s)
x.x.x.124:22 (t/o: 6s)
x.x.x.242:22 (t/o: 5s)

The tool also has the ability to do more than a passive banner grab. It includes other scan modes in which it will try to identify TLS servers by sending it a TLS NULL probe and identify HTTP servers.

Wednesday, July 29, 2015

Black Hat and DEF CON: Hacks and Fun

The great annual experience of Black Hat and DEF CON starts in just a few days, and we here at IOActive have a lot to share. This year we have several groundbreaking hacking talks and fun activities that you won’t want to miss!

For Fun
Join IOActive for an evening of dancing
Our very own DJ Alan Alvarez is back – coming all the way from Mallorca to turn the House of Blues RED. Because no one prefunks like IOActive.
Wednesday, August 5th
House of Blues

Escape to the IOAsis – DEF CON style!
We invite you to escape the chaos and join us in our luxury suite at Bally’s for some fun and great networking.  
Friday, August 7th12–6PM
Bally’s penthouse suite
·      Unwind with a massage 
·      Enjoy spectacular food and drinks 
·      Participate in discussions on the hottest topics in security 
·      Challenge us to a game of pool! 

After a two year hiatus, we’re bringing back the party and taking it up a few notches. Join DJs Stealth Duck, Alan Alvarez, and Keith Myers as they get our booties shaking. All are welcome! This is a chance for the entire community to come together to dance, swim, laugh, relax, and generally FREAK out!
And what’s a FREAKFEST without freaks? We are welcoming the community to go beyond just dancing and get your true freak on.
Saturday, August 8th
10PM till you drop
Bally’s BLU Pool

For Hacks
Escape to the IOAsis – DEF CON style!
Join the IOActive research team for an exclusive sneak peek into the world of IOActive Labs. 
Friday, August 7th
Bally’s penthouse suite

Enjoy Lightning Talks with IOActive Researchers:
Straight from our hardware labs, our brilliant researchers will talk about their latest findings in a group of sessions we like to call IOActive Labs Presents:
·      Mike Davis & Michael Milvich: Lunch & Lab - an overview of the IOActive Hardware Lab in Seattle
Robert Erbes: Little Jenny is Export Controlled: When Knowing How to Type Turns 8th-graders into Weapons 
·      Vincent Berg: The PolarBearScan
·      Kenneth Shaw: The Grid: A Multiplayer Game of Destruction 
·      Andrew Zonenberg: The Anti Taco Device: Because Who Doesn’t Go to All This trouble? 
·      Sofiane Talmat: The Dark Side of Satellite TV Receivers 
·      Fernando Arnaboldi: Mathematical Incompetence in Programming Languages 
·      Joseph Tartaro: PS4: General State of Hacking the Console
·      Ilja Van Sprundel: An Inside Look at the NIC Minifilter

Black Hat/DEF CON

Speaker: Chris Valasek
Remote Exploitation of an Unaltered Passenger Vehicle
Black Hat: 3PM Wednesday, August 5, 2015
DEF CON: 2PM Saturday, August 8, 2015
In case you haven’t heard, Dr. Charlie Miller and I will be speaking at Black Hat and DEF CON about our remote compromise of a 2014 Jeep Cherokee ( While you may have seen media regarding the project, our presentation will examine the research at much more granular level. Additionally, we have a few small bits that haven’t been talked about yet, including some unseen video, along with a 90-page white paper that will provide you with an abundance of information regarding vehicle security assessments. I hope to see you all there!

Speaker: Colin Cassidy
Switches get Stitches
Black Hat: 3PM Wednesday, August 5, 2015
DEF CON: 4PM Saturday, August 8, 2015
Have you ever stopped to think about the network equipment between you and your target? Yeah, we did too. In this talk we will be looking at the network switches that are used in industrial environments, like substations, factories, refineries, ports, or other homes of industrial automation. In other words: DCS, PCS, ICS, and SCADA switches.
We'll be attacking the management plane of these switches because we already know that most ICS protocols lack authentication and cryptographic integrity. By compromising the switches an attacker can perform MITM attacks on a live processes.
Not only will we reveal new vulnerabilities, along with the methods and techniques for finding them, we will also share defensive techniques and mitigations that can be applied now, to protect against the average 1-3 year patching lag (or even worse, "forever-day" issues that are never going to be patched).

Speaker: Damon Small
Beyond the Scan: The Value Proposition of Vulnerability Assessment
DEF CON: 2PM Thursday, August 6, 2015
It is a privilege to have been chosen to present at DEF CON 23. My presentation, “Beyond the Scan: The Value Proposition of Vulnerability Assessment”, is not about how to scan a network; rather, it is about how to consume the data you gather effectively and how to transform it into useful information that will affect meaningful change within your organization.
As I state in my opening remarks, scanning is “Some of the least sexy capabilities in information security”. So how do you turn such a base activity into something interesting? Key points I will make include:
·      Clicking “scan” is easy. Making sense of the data is hard and requires skilled professionals. The tools you choose are important, but the people using them are critical.
·      Scanning a few, specific hosts once a year is a compliance activity and useful only within the context of the standard or regulation that requires it. I advocate for longitudinal studies where large numbers of hosts are scanned regularly over time. This reveals trends that allow the information security team to not only identify missing patches and configuration issues, but also to validate processes, strengthen asset management practices, and to support both strategic and tactical initiatives.
I illustrate these concepts using several case studies. In each, the act of assessing the network revealed information to the client that was unexpected, and valuable, “beyond the scan.”

Speaker: Fernando Arnaboldi
Abusing XSLT for Practical Attacks
Black Hat: 3:50PM Thursday, August 6, 2015
DEF CON: 2PM Saturday, August 8, 2015
XML and XML schemas (i.e. DTD) are an interesting target for attackers. They may allow an attacker to retrieve internal files and abuse applications that rely on these technologies. Along with these technologies, there is a specific language created to manipulate XML documents that has been unnoticed by attackers so far, XSLT.
XSLT is used to manipulate and transform XML documents. Since its definition, it has been implemented in a wide range of software (standalone parsers, programming language libraries, and web browsers). In this talk I will expose some security implications of using the most widely deployed version of XSLT.

Speaker: Jason Larsen
Remote Physical Damage 101 – Bread and Butter Attacks
Black Hat: 9AM Thursday, August 6, 2015

Speaker: Jason Larsen
Rocking the Pocket Book: Hacking Chemical Plant for Competition and Extortion
DEF CON:  6PM Friday, August 7, 2015

Speaker: Kenneth Shaw
The Grid: A Multiplayer Game of Destruction
DEF CON: 12PM Sunday, August 9, 2015, IoT Village, Bronze Room
Kenneth will host a table in the IoT Village at DEF CON where he will present a demo and explanation of vulnerabilities in the US electric grid.

Speaker: Sofiane Talmat
Subverting Satellite Receivers for Botnet and Profit
Black Hat: 5:30PM Wednesday, August 5, 2015
Security and the New Generation of Set Top Boxes
DEF CON: 2PM Saturday, August 8, 2015, IoT Village, Bronze Room
New satellite TV receivers are revolutionary. One of the devices used in this research is much more powerful than my graduation computer, running a Linux OS and featuring a 32-bit RISC processor @450 Mhz with 256MB RAM.
Satellite receivers are massively joining the IoT and are used to decrypt pay TV through card sharing attacks. However, they are far from being secure. In this upcoming session we will discuss their weaknesses, focusing on a specific attack that exploits both technical and design vulnerabilities, including the human factor, to build a botnet of Linux-based satellite receivers.

Speaker: Alejandro Hernandez
Brain Waves Surfing - (In)security in EEG (Electroencephalography) Technologies
DEF CON: 7-7:50PM Saturday, August 8, 2015, BioHacking Village, Bronze 4, Bally's
Electroencephalography (EEG) is a non-invasive method for recording and studying electrical activity (synapse between neurons) of the brain. It can be used to diagnose or monitor health conditions such as epilepsy, sleeping disorders, seizures, and Alzheimer disease, among other clinical uses. Brain signals are also being used for many other different research and entertainment purposes, such as neurofeedback, arts, and neurogaming.
I wish this were a talk on how to become Johnny Mnemonic, so you could store terabytes of data in your brain, but, sorry to disappoint you, I will only cover non-invasive EEG. I will cover 101 issues that we all have known since the 90s, that affect this 21st century technology.
I will give a brief introduction of Brain-Computer Interfaces and EEG in order to understand the risks involved in brain signal processing, storage, and transmission. I will cover common (in)security aspects, such as encryption and authentication as well as (in)security in design. Also, I will perform some live demos, such as the visualization of live brain activity, sniffing of brain signals over TCP/IP, as well as software bugs in well-known EEG applications when dealing with corrupted brain activity files. This talk is a first step to demonstrating that many EEG technologies are vulnerable to common network and application attacks.