From pgrundl@kpmg.dk Thu Mar 21 23:16:42 2002 From: "[iso-8859-1] Peter Gründl" To: bugtraq Date: Mon, 18 Mar 2002 10:39:07 +0100 Subject: KPMG-2002005: BitVise WinSSH Denial of Service [The following text is in the "iso-8859-1" character set] [Your display is set for the "US-ASCII" character set] [Some characters may be displayed incorrectly] -------------------------------------------------------------------- -=>BitVise WinSSH Denial of Service<=- courtesy of KPMG Denmark BUG-ID: 2002005 Released: 18th Mar 2002 -------------------------------------------------------------------- Problem: ======== Using "ill-intended connection attempts", a malicious user could bring the server to a state where it would no longer accept incoming SSH connections. Vulnerable: =========== - BitVise WinSSH prior to build 2002-03-16 on Windows 2000 Server Details: ======== Due to differences in the SSHd and the underlying socket layer, it was possible to abruptly end sessions and not have those freed properly by the sshd. Each incomplete connection would use up a few memory handles and allocate nonpaged kernel memory. Windows can only handle a certain amount of kernel memory being allocated, after that point most applications begin acting peculiar. During testing we repeatedly caused the server to no longer accept connections to port 22 (connection refused). This took about 1840x254 connections, but since it's not time or bandwidth related, this attack could be carried out from a normal modem dialup, and still be succesful. The vendor has limited the amount of simultaneous unathenticated sessions and put a timeout of 60 seconds on each connection. Vendor URL: =========== You can visit the vendors webpage here: http://www.bitvise.com Vendor response: ================ The vendor was contacted on the 25th of February, 2002. On the 16th of March the vendor released the new build, that corrected the issue. On the 18th of January, 2002, it was confirmed that the patch corrected the issue mentioned in this advisory. Corrective action: ================== Upgrade to the latest build, which can be downloaded here: http://www.bitvise.com/existing-users.html Author: Peter Gründl (pgrundl@kpmg.dk) -------------------------------------------------------------------- KPMG is not responsible for the misuse of the information we provide through our security advisories. These advisories are a service to the professional security community. In no event shall KPMG be lia- ble for any consequences whatsoever arising out of or in connection with the use or spread of this information. --------------------------------------------------------------------