SSH's Secure Shell for Windows 2.4 Can Be Crashed By Remote Users
SecurityTracker Alert ID: 1001087|
SecurityTracker URL: http://securitytracker.com/id/1001087
(Links to External Site)
Date: Mar 15 2001
Denial of service via network|
Fix Available: Yes Vendor Confirmed: Yes |
Version(s): 2.4 for Windows Only|
USSR Labs announced discovery of a denial of service condition in the Windows version of SSH's Secure Shell (SSHD) in which a remote user with access to the sshd port can cause the sshd process to crash.|
The server crashes due to an issue with adjacent connection handling where the sshd server is unable to handle 64 or more simulataneous connections. If this number of simultaneous connections are presented to the server, the sshd process will crash, and no connections to the sshd process will be accepted.
The problem reportedly exists in ssheloop.c where the SshEventLoop fails.
See USSR Advisory Code USSR-2001001 for more information.
A remote user with access to the sshd port can cause the sshd process to crash.|
The vendor is releasing SSH Secure Shell for Windows Server 2.5 to correct the problem.|
Vendor URL: www.ssh.com (Links to External Site)
Exception handling error|
|Underlying OS: Windows (NT), Windows (2000)|
This archive entry has one or more follow-up message(s) listed below.|
Source Message Contents
Subject: Remote DoS attack against SSH Secure Shell for Windows Servers|
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Buenos Aires, Argentina
Topic: Remote DoS attack against SSH Secure Shell for
Windows Servers Vulnerability
USSR Advisory Code: USSR-2001001
Credits: Luciano Martins <firstname.lastname@example.org>
Affects: SSH Secure Shell for Windows Server 2.4
Corrected: SSH Secure Shell for Windows Server 2.5 available
Vendors Affected: SSH Communications Security Corp
UssrLabs has recently discovered a problem with Windows versions of
The problem lies with adjacent connection handling where the sshd is
unable to handle 64 simulataneous connections. As a result the sshd
crash, and no services to the sshd will be accepted.
The problem lies in ssheloop.c where the assertion test fails.
The Event Log displays the following code after 64 connections are
FATAL ERROR: E:\src\lib\sshutil\ssheloop\win32\ssheloop.c:1597
(function name unavailable) Assertion failed:
ssh_adt_num_objects(ssh_eloop_events) < 64
No doubt, proper error handling techniques have not been implemented
the SshEventLoop which ultimately causes the crash.
This results in a Denial of Service against the service in question.
2. Vendor Status:
official fix will be available soon.
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