what you don't know can hurt you
Home Files News &[SERVICES_TAB]About Contact Add New


Posted Jul 24, 2002
Authored by Robert

All versions of SSH and OpenSSH which use computability mode 1.99 are vulnerable to a mitm attack without the duplicate key warning because the attacker can force protocol version 1, so the only warning the user gets asks him if he wants to add the new key. Still suspicious, but less so.

tags | protocol
SHA-256 | 98d4d1bb0a58e04cbf0d8839a3f693e46ecfcac7a397eef7bae93eb8985ab548


Change Mirror Download

Hash: SHA1

SSH Protocol Weakness Advisory
Monday, July 22 2002
- - rtm

OK, here it is guys... I saw this today when I was looking at the newest issue of phrack (59)
and I discovered that an old little technique of SSH man in the middle attacks I had been working
on was now part of a Phrack article....
Luckily, source code hadn't been disclosed yet, and neither will mine. I just wanted to get this
issue out in the open so people could secure themselves while they can.
Remember, that the ssh daemon

So far, all vendors are vulnerable to this little trick, including commercial based SSH and OpenSSH.

You can find more details about the attack at http://www.sekurityfocus.com/phrack59/

Basically, ssh daemons advertise one of two major versions, depending on what is supported by the
software /configuration files, for SSH protocol version 1, or 2. Compatibility mode is enabled with a
version of 1.99. It is servers which advertise this compatibility mode of 1.99 which are vulnerable to
the attack. Servers in compatability mode have both protocols 1 and 2 enabled.
If the client has a key enabled for say, only SSH protocol 1 or 2, the malicious interloper, "Mallory,"
using ssh mitm arp techniques which are available in say, ettercap or dsniff, can advertise the opposite
protocol in the fake sshd version string used in the banner handshake.
If a client has only used say, SSH 1 authentication in the past, it will not contain a SSH2 key, so
no "Host Identification has changed" message will be present when the fake server advertises its public
host key. The targeted victim will only see a "KEY NOT PRESENT" prompt and will be asked if they want
to add the key.
Obviously, this removes some of the fear paranoid users would feel when facing a real mitm attack.
Remember, this is not a direct vulnerability in the SSH 1 or 2 protocols, but rather a slight trick that
can be abused.

- -------------------
Check known_hosts and known_hosts2 in your ~/.ssh directory, and check to see which keys you use for each host.
If you only use ssh1, force the ssh protocol to protocol 1, by specifying the -1 option.
Or if you use ssh2, force the ssh protocol 2 with the -2 option.
If you receive a hostkey change identification, you know something must be up!

Disable sshd? <- Isn't this always the best security approach, especially now? :)
Really, there isn't anything to do except mail users and tell them which protocol to force, and to ensure
that strict host key checking is always on!

I guess we'll have to wait for the vendors to release an inventive patch for this one...
Now, what I want to know is why somebody who works at SuSE has not been publishing these details openly!?!

A concerned citizen,
- -Robert
Version: Hush 2.1
Note: This signature can be verified at https://www.hushtools.com


Communicate in total privacy.
Get your free encrypted email at https://www.hushmail.com/?l=2

Looking for a good deal on a domain name? http://www.hush.com/partners/offers.cgi?id=domainpeople

Login or Register to add favorites

File Archive:

October 2022

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Oct 1st
    10 Files
  • 2
    Oct 2nd
    0 Files
  • 3
    Oct 3rd
    12 Files
  • 4
    Oct 4th
    15 Files
  • 5
    Oct 5th
    18 Files
  • 6
    Oct 6th
    16 Files
  • 7
    Oct 7th
    0 Files
  • 8
    Oct 8th
    0 Files
  • 9
    Oct 9th
    0 Files
  • 10
    Oct 10th
    0 Files
  • 11
    Oct 11th
    0 Files
  • 12
    Oct 12th
    0 Files
  • 13
    Oct 13th
    0 Files
  • 14
    Oct 14th
    0 Files
  • 15
    Oct 15th
    0 Files
  • 16
    Oct 16th
    0 Files
  • 17
    Oct 17th
    0 Files
  • 18
    Oct 18th
    0 Files
  • 19
    Oct 19th
    0 Files
  • 20
    Oct 20th
    0 Files
  • 21
    Oct 21st
    0 Files
  • 22
    Oct 22nd
    0 Files
  • 23
    Oct 23rd
    0 Files
  • 24
    Oct 24th
    0 Files
  • 25
    Oct 25th
    0 Files
  • 26
    Oct 26th
    0 Files
  • 27
    Oct 27th
    0 Files
  • 28
    Oct 28th
    0 Files
  • 29
    Oct 29th
    0 Files
  • 30
    Oct 30th
    0 Files
  • 31
    Oct 31st
    0 Files

Top Authors In Last 30 Days

File Tags


packet storm

© 2022 Packet Storm. All rights reserved.

Hosting By