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Vulnerability Note VU#419241

Multiple vendor SFTP logging format string vulnerability

Overview

A logging function used by multiple vendors' SFTP servers contains a format string vulnerability, which may allow an authorized remote attacker to execute arbitrary code or cause a denial of service.

I. Description

SFTP

SFTP (Secure FTP) is a file transfer application that uses SSH for encryption.

The problem

The logging function of several vendors' SFTP servers contains a format string vulnerability.

Vulnerable products include:

  • Reflection for Secure IT UNIX Server version 6.0
  • Reflection for Secure IT Windows Server version 6.0
  • F-Secure SSH Server for Windows version 5.x
  • F-Secure SSH Server for UNIX version 3.x through 5.x

II. Impact

A remote authenticated attacker may be able to execute arbitrary code with the privilege of the user or cause a denial of service to the SSH server.

III. Solution

Upgrade or patch


AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882.


According to the WRQ Tech note, the following workaround may prevent exploitation of the vulnerability:

    On UNIX Servers

       1. Edit the SSH server's sshd2_config file:

             1. Change the line

                subsystem-sftp internal://sftp-server

                to

                subsystem-sftp sftp-server

                Note: This change disallows the use of chroot.

             2. Comment out the SftpSyslogFacility keyword line. Note: The line should begin with two "pound" signs, as in this example:

                ## SftpSyslogFacility LOCAL7

       2. Restart the SSH server to read the changes in the configuration file.

    On Windows Servers
    The only workaround is to disable the sftp subsystem as follows:

       1. Edit the SSH server's sshd2_config file and comment out the subsystem-sftp line. Note: The line should begin with two "pound" signs, as in this example:

                ## subsystem-sftp "fsshsftpd.exe"

       2. Restart the SSH server to read the change in the configuration file.

    Systems Affected
    VendorStatusDate Updated
    BitviseNot Vulnerable17-Jan-2006
    F-Secure CorporationVulnerable15-Feb-2006
    FiSSHUnknown16-Jan-2006
    InterSoft InternationalNot Vulnerable18-Jan-2006
    lshUnknown16-Jan-2006
    MacSSHNot Vulnerable16-Jan-2006
    OpenSSHUnknown16-Jan-2006
    OSSHNot Vulnerable16-Jan-2006
    Pragma SystemsUnknown16-Jan-2006
    PuTTYNot Vulnerable16-Jan-2006
    TTSSHUnknown16-Jan-2006
    VanDyke SoftwareNot Vulnerable17-Jan-2006
    WinSCPUnknown16-Jan-2006
    WRQ, Inc.Vulnerable15-Feb-2006

    References



http://support.wrq.com/techdocs/1882.html

Credit

Thanks to WRQ for reporting this vulnerability.

This document was written by Will Dormann.

Other Information

Date Public02/13/2006
Date First Published02/13/2006 04:20:30 PM
Date Last Updated02/15/2006
CERT Advisory 
CVE-ID(s) 
NVD-ID(s) 
US-CERT Technical Alerts 
Metric3.37
Document Revision9

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