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iDEFENSE Security Advisory 01.28.03: SSH2 Clients Insecurely Store
Passwords (AbsoluteTelnet, SecureCRT, Entunnel, SecureFx, and PuTTY)
http://www.idefense.com/advisory/01.28.03.txt
January 28, 2003

I. BACKGROUND

PuTTY is a free implementation of Telnet and SSH for Win32 platforms,
along with an xterm terminal emulator. More information is available at
http://www.chiark.greenend.org.uk/~sgtatham/putty/.

SecureCRT provides security for remote access, file transfer, and data
tunneling by combining the open Secure Shell protocol with emulation.
Entunnel provides SSH2 data tunneling (port forwarding) services when
connected to an SSH2 server. The SecureFX client application is an SFTP
and FTP over an encrypted SSH2 client. More information is available at
www.vandyke.com/products.

AbsoluteTelnet is a terminal client program developed for the Microsoft
Windows platform. AbsoluteTelnet supports multiple protocols including
Telnet, SSH1, SSH2, TAPI Dialup and direct COM. More information is
available at http://www.celestialsoftware.net/telnet/index.html.

II. DESCRIPTION

AbsoluteTelnet, SecureCRT, Entunnel, SecureFx, and PuTTY do not properly
scrub memory allowing an attacker with access to memory or a memory dump
to retrieve authentication information.

When connected via SSH2, an attacker can search memory or a memory dump
for logon credentials. Passwords transmitted by PuTTY can be found by
searching for the second occurrence of the string "password:". The user's
password is stored in plaintext shortly after this string. Passwords
transmitted by SecureCRT can be found by searching for the string
"ssh-connection". The logon and password is stored in plaintext on the
respective sides of this keyword. Passwords transmitted by AbsoluteTelnet
can be found by searching for the first occurrence of the string
"Password", that lies in a segment of read/write memory. The logon and
password is stored in plaintext on the respective sides of this keyword.

III. ANALYSIS

An attacker able to ascertain a target user's memory dump will be able to
recover passwords for remote systems. This is of special concern in shared
environments.

IV. DETECTION

iDEFENSE has verified the existence of this vulnerability in the following
versions of the above mentioned clients:

• AbsoluteTelnet: latest (2.11)
• SecureCRT: latest (4.0.2) and 3.4.6
• SecureFX : 2.1.2 and 2.0.4
• Entunnel: 1.0.2 and earlier
• PuTTY: latest (0.53b)

Earlier versions of the tested clients as well as other clients may be
vulnerable as well.

V. VENDOR RESPONSE(S)/FIX

Current development snapshots of PuTTY are believed to have this problem
fixed. Unfortunately, we are in the middle of heavy code restructuring and
not currently in a position to make a stable release, but the current
snapshots should be good enough for anyone for whom this is a problem.
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The SSH password vulnerability discovered by iDEFENSE has been found to
exist in all versions of AbsoluteTelnet prior to (and including) version
2.11.

Version 2.12, which Celestial Software will make available as a FREE
update to ALL existing users, fixes the problem by keeping password memory
"scrubbed" and free of plaintext copies of the password.

Version 2.12 is currently in beta testing pending the beta test group's
acceptance of the changes it contains.  Upon release, it will be available
for download at the Celestial Software website:

http://www.celestialsoftware.net/telnet

For a sneak peak at the 2.12 beta, go here:

http://www.celestialsoftware.net/telnet/beta_software.html

Thanks to iDEFENSE for bringing this to my attention and for allowing
adequate time to make corrections! In particular, thanks to David Endler
for staying on top of this!
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VanDyke Software recognizes the efforts of iDEFENSE in discovering this
security issue and commends iDEFENSE for the responsible manner in which
the security issue was made known so as to allow time for revisions to be
made before the information was released to the public.

The vulnerability reported by iDEFENSE exists in the following versions of
VanDyke Software client applications:

    SecureCRT: 4.0.2 and 3.4.7
    SecureFX : 2.1.2 and 2.0.4
    Entunnel: 1.0.2 and earlier

Earlier versions of these client applications are vulnerable as well.
VanDyke encourages all users whose licenses were purchased prior to June
1, 2000 to consider upgrading to the current version(s) of their licensed
applications.

Vulnerability fix downloads are available:
    SecureCRT 4.0.3 - http://www.vandyke.com/download/securecrt/index.html
    SecureCRT 3.4.8 -
http://www.vandyke.com/download/securecrt/3.4/index.html

    SecureFX 2.1.3 - http://www.vandyke.com/download/securefx/index.html
    SecureFX 2.0.5 -
http://www.vandyke.com/download/securefx/2.0/index.html

    Entunnel 1.0.3 - http://www.vandyke.com/download/entunnel/index.html
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VI. CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project
assigned the following identification numbers to these issue:

CAN-2003-0046 - AbsoluteTelnet
CAN-2003-0047 - SecureCRT
CAN-2003-0048 - PuTTY, SecureFx, and Entunnel

VII. DISCLOSURE TIMELINE

12/13/2002      Issues disclosed to iDEFENSE
01/09/2003      putty@projects.tartarus.org, Mark.Walker@vandyke.com, and 
                bpence@celestialsoftware.net notified
01/09/2003      iDEFENSE clients notified
01/09/2003      Response received from Simon Tatham [anakin@pobox.com]
01/10/2003      Response received from Celestial Software 
                [bpence@mindspring.com]  
01/10/2003      Response received from Van Dyke Software 
                [mark.walker@vandyke.com]
01/28/2003      Coordinated public disclosure

VIII. CREDIT

Knud Erik Højgaard (knud@skodliv.dk) discovered these vulnerabilities.

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