Multiple vendor SFTP logging format string vulnerability
Vulnerability Note VU#419241
Original Release Date: 2006-02-13 | Last Revised: 2006-02-15
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.
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
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.
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.
Notified: January 16, 2006 Updated: February 15, 2006
Status
Affected
Vendor Statement
Products Affected:
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
Problem Correction:
AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882 ( http://support.wrq.com/techdocs/1882.html).
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.
AttachmateWRQ also recommends that you bookmark and regularly check the Security Updates and Reflection for Secure IT web page for the latest information about updates and vulnerabilities: http://support.wrq.com/techdocs/1910.html
Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.
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
Problem Correction:
AttachmateWRQ Reflection for Secure IT and F-Secure SSH Server users should install an upgrade, as specified in WRQ Tech Note 1882 ( http://support.wrq.com/techdocs/1882.html).
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.
AttachmateWRQ also recommends that you bookmark and regularly check the Security Updates and Reflection for Secure IT web page for the latest information about updates and vulnerabilities: http://support.wrq.com/techdocs/1910.html
Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.
Notified: January 16, 2006 Updated: January 17, 2006
Status
Not Affected
Vendor Statement
Our SSH server for Windows, WinSSHD, does not share codebase with affected versions of AttachmateWRQ's server. Thus, WinSSHD is not affected by this vulnerability.
Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.
Notified: January 16, 2006 Updated: January 16, 2006
Status
Not Affected
Vendor Statement
PuTTY's SSH and SFTP implementations are not derivatives of anybody else's. In addition, the PuTTY code base does not include an SSH or SFTP server at all. We cannot be affected by this issue.
Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.
Notified: January 16, 2006 Updated: January 17, 2006
Status
Not Affected
Vendor Statement
VanDyke Software's VShell(R) Server for Windows and VShell
Server for UNIX products are not affected by the issues described in VU#419241. VShell does not share any common SFTP code with Reflection/F-Secure products.
Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.