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SSH2 Clients Insecurely Store Passwords

01.28.03

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.

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 more easily.

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.

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.

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.

VENDOR RESPONSE

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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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, SecureFx, and Entunnel
CAN-2003-0048 - PuTTY

DISCLOSURE TIMELINE

12/13/2002       Issues disclosed to iDEFENSE
01/09/2003       putty@projects.tartarus.org, Mark.Walker@vandyke.com, and
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
01/10/2003       Response received from Van Dyke Software
01/28/2003       Coordinated public disclosure

CREDIT

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