Re[2]: Why TCP is more secure than UDP?

Hello Buz,

Thank you for your details.
What you describe looks to me like some land or smurf-attack.
Let me go on...
i) using the conf. you describe, if i understand you well, even 1
legitime ECHO will start some pending of packets.
ii) as you describe it is for me a M-I-T-M attack where you basicaly
spoof an IP

The point that you use TCP ur UDP doesnt really matter, because as i
mentioned, the only thing which makes TCP harder to break is the
pre-established connection with the seq-number.
Taking this in consideration, if Moe sniffs the traffic he can hijack
the TCP-Session or try to guess the seq-nr.
But as i mentioned, we dont spoof here TCP or UDP, we basicaly spoof
an IP and start an man in the middle (M-I-T-M) attack on the
respective protocol.

Best regards,
Adam Pal

Considering your scenario, if the router is configured
not to accept inbound traffic with rfc-1918 source-addresses everything is ok.
From that point of view it can be also a weakness of the router conf.
more than a weakness of the protocol? :)

Wednesday, July 11, 2007, 9:18:42 PM, you wrote:

<==============Original message text===============
BD> I'll try and illustrate a security difference. Lets say I have a
BD> service called "Echo" that runs on both udp port 7 and tcp port 7 on
BD> two machines on my lan (192168.1.1 or "Larry" and or
BD> "Curly".) Suppose this service just echoes back any packet I send it.
BD> Suppose my tricky friend "Moe" is across the internet at (Oh
BD> yeah - and let's also suppose these are not rfc 1918 addresses.) Moe's
BD> router and ISP are configured kinda loosely and don't really care
BD> about source addresses, just destination.

BD> If Moe uses a UDP packet with source and destination
BD>, his first packet could (if My router configs are a
BD> little loose) get that packet to Larry, the content of that packet
BD> "SLAP" will get echoed to Curly who will then SLAP Larry who will
BD> then SLAP Curly ad inifinitum. Burning network and CPU until noticed.
BD> (works well actually with port 19 and Chargen as one of the ports and
BD> 7 as the other.)

BD> If Moe uses a tcp packet with source and a destination
BD> of His packet will get to Larry and Larry will try and
BD> handshake with Curly who won't have any idea of what's going on and
BD> stop the transaction.

BD> It's easy for Moe to "spoof" either udp or tcp but the udp packet is
BD> more fun for Moe.

BD> Luck,
BD> Buz

BD> On 7/10/07, pal_adam@xxxxxxx <pal_adam@xxxxxxx> wrote:

I dont understand what you mean by spoofing, since wherever you
use UDP or TCP the underlying layer still remains IP so when you
spoof a source you spoof an IP source.
If you talk about a man-in-the-middle attack then taking a
closer look at both protocols will show that UDP doesnt establish
any connection before starting the communication.
Using TCP you`ll need to ACK incomming data using a
pre-established sequence number which makes the attack on TCP
harder but not impossible.


Adam Pal

-------- Original-Nachricht --------
Datum: 10 Jul 2007 02:11:12 -0000
Von: paavan.shah@xxxxxxxxx
An: security-basics@xxxxxxxxxxxxxxxxx
Betreff: Why TCP is more secure than UDP?

It is said that UDP is considered more vulnerable to spoofing than TCP?

Can anyone point me to any document/link which describes TCP is more
secure than UDP

Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen!
Ideal für Modem und ISDN:

<===========End of original message text===========

Attachment: smime.p7s
Description: S/MIME Cryptographic Signature

Relevant Pages

  • Re: Incoherent E-mails
    ... The Novell crap was originally run on IPX ... The term in the early-mid nineties was "packet storm". ... The original advantage of UDP was ... > 60 bytes for TCP. ...
  • Re: recvfrom() strange operation
    ... I have only one escape way for this kind of UDP operation. ... TCP receive you always send data to upper level in sequence, ... In case of UDP you do not know the packet ...
  • Re: TCP Blocking sockets
    ... the tcp buffers don't fill up etc due to slow link speeds. ... With TCP/IP the receiving system will wait for the packet to ... >arrives, ... UDP doesn't ensure you data delivery, ...
  • Re: A question regarding MTU: how it can effect TCP performance + other queries
    ... Can you check if your physical NIC has TCP large send offload enabled? ... I can't think of anything for the UDP case however, that just seems strange to me. ... Are you grouping multiple UDP packets in one TCP packet? ... encapsulated within another TCP packet when passed to physical interface, while for UDP I am sending UDP packet encapsulated within TCP packet when passed to physical interface. ...
  • Re: HTTP over both TCP and UDP
    ... but we're not talking about using UDP. ... with TCP packets. ... routers, and the server. ... you put a sequence number in the UDP packet. ...