ARPFreeze is a nice GUI for Windows that allows to configure static ARP entries very easily, and makes these changes persistent after reboot.
Thus does it protect the client machine against ARP flooding.
It works for both Windows Vista and prior versions (support of arp -s and netsh).
Detectpromisc is a python script based on Scapy, that allows to detect if a computer is sniffing the network.
By nature, it is quite difficult to detect if a machine is sniffing, because it operates passively, receiving all packets from the wire but, normaly, answering only to packets destinated to itself.
There are however several methods that make the detection possible.
Some are based on the latency, because in promiscuous mode a machine will take more time to answer (packets have to be processed by the kernel, not the network card only).
Another imply to generate some tricky packets, with a correct IP but a wrong MAC address. The machine should answer only if it is in spoofing mode.
It is also possible to use source-routing with a host on the path that doesn’t route. If an answer comes back anyway, the target is sniffing.
Other methods are implemented by IDS and based on the volume of DNS requests.
Most of these methods are not necessarily reliable, easy to implement. All the ones based on IP routing are quite easy to workaround by the attacker.
Detectpromisc works exclusively at the ARP level.
According to the OS, it sends out some specific ARP packets (multicast, fake broadcast…).
In normal mode, the network card will discard theses illegitimate packets : they call it the hardware filter.
In promiscuous mode, there is no hardware filter : packets reaches directly the kernel (software filter).
Of course, according to the OS, the kernel will behave differently, but some tricked ARP packets generated by Detectpromisc will cause the sniffing machine to send an answer.
It is therefore possible to differenciate a sniffing machine from a normal machine. Plus, as it is quite reliable and OS specific, it is possible to fingerprint the target.
In practice, it has worked very well so far :
% sudo ./detect.py -i eth0 -O 192.168.222.25 Scan right index finger on UPEK TouchStrip WARNING: No route found for IPv6 destination :: (no default route?) 192.168.222.25 : promiscuous mode card detected probably: Linux 2.2/2.4/2.6 % sudo ./detect.py -i eth0 -O 192.168.222.26 WARNING: No route found for IPv6 destination :: (no default route?) 192.168.222.26 : promiscuous mode card detected probably: Windows 2k/NT4
A full paper on how it works is there. Great tool, isn’t it ?
Edward Bjarte Fjellskål contacted me to let me know about a new program he, Kacper Wysocki and Jan Henning Thorsen made, called Prads.
Prads is a fingerprinting scanner, coded in Perl. I am fond of this kind of tool, so I enjoyed checking it out.
Prads operates differently from Nmap or SinFP that I already introduced on this blog. It works passively, meaning that it aims to scan systems without sending out a single packet. It does this by capturing the traffic silently though an interface in promiscuous mode.
The advantage, of course, is that it is much more stealth than a classic scanner, which leaves usually a lot of log entries in firewalls or IDS.
It works on several layers and is based on all the common protocols, that should make it efficient and fast : TCP, UDP, ICMP, ARP.
Using Prads is very simple, just look at prads –help for more info.
There is a sample output, after running it a few seconds on my network :
% sudo perl prads.pl -d eth0 --os --service Starting prads.pl... Using eth0 DBD::SQLite::db prepare failed: table asset already exists(1) at dbdimp.c line 271 at prads.pl line 320. 1243801518 [SYN ] ip: 192.168.222.23 - Linux - 2.6 (newer, 7) [S4:64:1:60:M1460,S,T,N,W7:.] distance:0 link:"ethernet/modem" 1243801518 [SYNACK ] ip: 192.168.222.254 - Linux - 2.6 (newer, 0) [5792:64:1:60:M1460,S,T,N,W0:ZA] distance:0 link:"ethernet/modem" ; 3.0.10-1.1.1 Firefox [192.168.222.23:44555] distance:1 link:SERVICE 1243801518 [SERVICE ] ip: 192.168.222.254 - Unknown HTTP - HTTP; [192.168.222.254:80] distance:1 link:SERVICE ; 3.0.10-1.1.1 Firefox [192.168.222.23:44556] distance:1 link:SERVICE ; 3.0.10-1.1.1 Firefox [192.168.222.23:44557] distance:1 link:SERVICE ; 3.0.10-1.1.1 Firefox [192.168.222.23:44558] distance:1 link:SERVICE ; 3.0.10-1.1.1 Firefox [192.168.222.23:44559] distance:1 link:SERVICE 1243801536 [SYNACK ] ip: 91.121.56.96 - Linux - 2.6 (newer, 5) [5792:64:1:60:M1380,S,T,N,W5:ZA] distance:7 link:"GPRS, T1, FreeS/WAN" 1243801536 [SERVICE ] ip: 91.121.56.96 - Generic TLS 1.0 SSL - ; [91.121.56.96:443] distance:1 link:SERVICE 1243801438 [UDP ] ip: 192.168.222.23 - @Linux - 2.6 [20:64:1:.:2:0] distance:0 link:ethernet [OLD] 1243801438 [UDP ] ip: 89.2.0.1 - @Linux - 2.6 [20:64:1:.:2:0] distance:2 link:ethernet [OLD] 1243801544 [SERVICE ] ip: 89.2.0.1 - - - DNS; - [89.2.0.1:53] distance:1 link:SERVICE 1243801549 [SYNACK ] ip: 192.168.222.1 - Cisco - 7200, Catalyst 3500, etc [4096:255:0:44:M1460:A] distance:0 link:"ethernet/modem" 1243801549 [SERVICE ] ip: 192.168.222.1 - Cisco SSH - Protocol 1.5; 1.25 [192.168.222.1:22] distance:1 link:SERVICE 1243801549 [SERVICE ] ip: 192.168.222.23 - OpenSSH - Protocol 1.5; 5.1 [192.168.222.23:42208] distance:1 link:SERVICE 1243801600 [SYN ] ip: 192.168.222.23 - Linux - 2.6 (newer, 7) [S4:64:1:60:M1460,S,T,N,W7:.] distance:0 link:"ethernet/modem" [OLD] 1243802459 [SYNACK ] ip: 192.168.222.2 - UNKNOWN - UNKNOWN [8192:128:1:60:M1460,N,W8,S,T:A] distance:0 link:"ethernet/modem" 1243802459 [SERVICE ] ip: 192.168.222.23 - Windows SMB - ; [192.168.222.23:37748] distance:1 link:SERVICE 1243802459 [SERVICE ] ip: 192.168.222.2 - Windows SMB - ; [192.168.222.2:445] distance:1 link:SERVICE 1243801596 [SYNACK ] ip: 91.121.56.96 - Linux - 2.6 (newer, 5) [5792:64:1:60:M1380,S,T,N,W5:ZA] distance:7 link:"GPRS, T1, FreeS/WAN" [OLD] 1243801596 [SERVICE ] ip: 91.121.56.96 - Generic TLS 1.0 SSL - ; [91.121.56.96:443] distance:1 link:SERVICE [OLD] 1243801367 [UDP ] ip: 192.168.222.2 - @Windows - MS [20:128:0:.:0:0] distance:0 link:ethernet [OLD]
As you can see, there is already some interesting output.
It detected quite well my Linux laptop running Firefox (UPDATE : according to the author, it is a bug as client detection has not been implemented yet) and surfing a few website, the provider’s DNS servers, another Linux machine and a Windows desktop. Concerning the last two, I guess that a more completed signature database would have allowed a more precise fingerprinting. The Linux box is a wifi Linksys router and the Windows one runs Vista.
Also, the gateway curiously did not show up itself, but the presence of a SSH connection helped to find it.
Finally, there is a little incoherence between the distance shown for the DNS server (=2, correct) and for the service (=1).
To be honnest, so far, I had never found interest in the existing passive scanners. There were POf but it is now pretty outdated and seems not to be developped anymore. Ettercap could fingerprint the system seen while sniffing (profiles), but it was definitely too limited and not really furtive. Moreover, Nmap with the right options, or SinFP itself can be quite stealth.
But now Prads has a place among the tools I use. It is efficient, straight forward and provide some useful info, beyond the OS detection : service and client info, distance, etc. It is nice because, once again, all these data are obtained withou sending out any request at all.
As it is in its early stage, it is very promising and I am looking forward to Prads and its signature database improving. Please keep up the good job !
That’s all for today. This tour was short but I will write again about this tool, as I will be using it. The next post will probably introduce the way the signature database is built and how it can be extended. So keep wired and don’t forget to check the Prads homepage.
Video of a dummy vulnerability on Windows 7 . More info there.
It is incredible that Microsoft invests so much money in its security and that there are still such a bad security design for programs that in no way should be granted any administrator access (calc.exe or notepad.exe).
Also, I can’t imagine that no one could detect it in their teams during the quality process and security audit.
What the hell are they doing ?
Not long after md5, the computation progress has made another victim.
Last week, it was made public that the SHA-1 hash function should be now considered vulnerable. The discovery bring up that the computation to create a collision hash has been dramaticaly reduced. As a consequence, the SHA-1 function can’t warranty anymore the uniquity – and so the integrity – of the hashed object.
There are a few ressources :
This is the natural evolution of cryptography. Stronger cryptography is required against stronger CPU power. In this race, it is now suggested to migrate to SHA-2 whose digest lenghts range from 224 to 512 bits (instead of 160 bits for SHA-1). And until next time, where we will be urged to migrate to SHA-3 ;)
Debian, whose infrastructure was based on SHA-1 (package management, development) is quickly migrating all its keys right now. The procedure the Debian people should follow implies a transition period, where the new key will be signed with the former key, until the latter is revoked. Thus until all peers are updated too, to avoid breaking all the signing infrastruture.
Myself, I ugraded my keys from DSA/1024 bits to RSA/4096 bits (with SHA-2 hashing), so it should be ok for a while. You will find my new key here or linked from the contact page.
MD5 was found vulnerable a few years ago. Recently, a team succeeded in producing a fake CA SSL certificate.
MD5 or SHA-1 is the algorithm used to authenticate the peer in SSL messages. If it gets compromised, and using various combined technics, it becomes possible to do a MiM attack.
But too much noise has been made about it. There is a nice reaction.
Indeed, it still requires a lot of efforts and conditions for the attack to be possible. And the CPU power is still huge : the researchers used not less than a cluster of 200 PS3 to drive the attack. Even with that hardware and engineering, it took until 3 days of intensive computation.
Not everyone can afford it, nor would have much motivation to attack a single user like this.
Security has always been a compromise between usuability and risk. Today, the risk concerning MD5 is still low enough to stop this wind of panic.
Let’s begin the migration to SHA-1 quietly.