RE: IPSec with Preshared secret warning.
- From: "Thomas W Shinder" <tshinder@xxxxxxxxxxxxxxxxxx>
- To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
- Date: Mon, 5 May 2003 19:33:52 -0500
Hi John,
Found it!
http://support.microsoft.com/?kbid=257225
How's that for good security planning on Microsoft's part?
Thanks!
Tom
Thomas W Shinder
www.isaserver.org/shinder
ISA Server and Beyond: http://tinyurl.com/1jq1
Configuring ISA Server: http://tinyurl.com/1llp
-----Original Message-----
From: Thomas W Shinder
Sent: Monday, May 05, 2003 6:51 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: IPSec with Preshared secret warning.
http://www.ISAserver.org
Hi John,
With Deb's help, I found some good info on Aggressive Mode. AFAIK, Win2k
and Win2003 use Main and Quick Modes, but I don't think they fall back
on, or support Aggressive Mode. If they do, I've never read anything
about it, or they are using different terminology.
Thanks!
Tom
Thomas W Shinder
www.isaserver.org/shinder
ISA Server and Beyond: http://tinyurl.com/1jq1
Configuring ISA Server: http://tinyurl.com/1llp
-----Original Message-----
From: Thomas W Shinder
Sent: Monday, May 05, 2003 6:35 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: IPSec with Preshared secret warning.
http://www.ISAserver.org
Hi John,
Pretty interesting stuff. But, maybe somebody smart than me can explain
what "aggressive mode" is? I notice the neologism.com site mentions that
its possible and that they did it, but didn't mention how long the key
was (probably used "mom" for the preshared key, bet it took a long time
to figure that one out)l. But seriously, I would be interesting to know
how long it would take to crack a key that was more than 8 characters,
that had both upper and lower case letters, numbers and symbols in it,
that didn't use the @ for the letter A :-)
Thanks!
Tom
Thomas W Shinder
www.isaserver.org/shinder
ISA Server and Beyond: http://tinyurl.com/1jq1
Configuring ISA Server: http://tinyurl.com/1llp
-----Original Message-----
From: John Tolmachoff (Lists) [mailto:johnlist@xxxxxxxxxxxxxxxxxxx]
Sent: Monday, May 05, 2003 5:22 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] IPSec with Preshared secret warning.
http://www.ISAserver.org
FYI, copied from the SANS Critical Vulnerability Analysis Vol 2 No 17
(3) HIGH: IPSec Aggressive Mode Preshared Secret Exposure
Affected Products:
IPSec servers that support "aggressive" mode authentication with
preshared
secrets
Description:
When operating in aggressive mode, an IPSec server provides a connecting
client with a cleartext hash value derived from the preshared secret.
Attackers can collect a copy of the hash by sniffing an attempt to
establish
a VPN tunnel (the attempt can fail). The hash can then be used in an
offline
dictionary attack to recover the preshared secret. VPN gateways that
accept
connection requests from arbitrary IP addresses are especially at risk.
Note
that some servers (e.g. Cisco routers) will automatically switch to
aggressive mode if the client requests it. This attack has been known
for
some time to security researchers but has not been widely publicized.
Proof-of- concept tools is available to retrieve the hash from a
vulnerable
server and execute the dictionary attack to recover the preshared
secret.
Council Site Actions:
Most of the reporting council sites do not use preshared secrets for
their
VPN connections and most have "Aggressive Mode" set to "false" on their
concentrators. Several of the sites do have limited uses of preshared
keys
and stated that in these cases they use strong, random secrets. Also,
some
of these sites restrict the VPN connections by IP address.
Risk: Remote attackers can recover the preshared secret and authenticate
to
the VPN gateway as a valid user.
Deployment: Widely deployed.
Many VPN products support aggressive mode by default, and are configured
to
accept connections from any IP address in order to support traveling
employees.
Ease of Exploitation: Trivial.
Tools are available to automate the hash collection and cracking
process.
The password guessing task can be split across multiple machines running
in
parallel for greater speed.
Status: Confirmed.
If preshared secrets and aggressive mode authentication must be used,
"strong" secrets that are unlikely to be cracked in a dictionary attack
should be selected and changed periodically. If possible, aggressive
mode
can be disabled in favor of main mode authentication.
References:
Paper by Michael Thurman describing the attack
http://archives.neohapsis.com/archives/bugtraq/2003-04/0274.html
Posting by Damir Rajnovic, Cisco PSIRT
http://archives.neohapsis.com/archives/bugtraq/2003-04/0285.html
Posting by Curt Sampson
http://archives.neohapsis.com/archives/bugtraq/2003-04/0322.html
IKECrack Tool
http://ikecrack.sourceforge.net/
Posting by Anton Rager, IKECrack Author
http://archives.neohapsis.com/archives/bugtraq/2003-04/0306.html
SecurityFocus BID (published October 1999)
http://www.securityfocus.com/bid/7423/info/
John Tolmachoff MCSE CSSA
Engineer/Consultant
eServices For You
www.eservicesforyou.com
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