Remote DoS attack against SSH Secure Shell for Windows Servers Vulnerability

Type securityvulns
Reporter Securityvulns
Modified 2001-03-15T00:00:00



                               U.S.S.R labs
                         Buenos Aires, Argentina

Topic: Remote DoS attack against SSH Secure Shell for Windows Servers Vulnerability USSR Advisory Code: USSR-2001001 Announced: 2001-03-16 Credits: Luciano Martins <> Affects: SSH Secure Shell for Windows Server 2.4 Corrected: SSH Secure Shell for Windows Server 2.5 available soon Vendors Affected: SSH Communications Security Corp

  1. Discussion

UssrLabs has recently discovered a problem with Windows versions of sshd. The problem lies with adjacent connection handling where the sshd is unable to handle 64 simulataneous connections. As a result the sshd will 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 spawned:

FATAL ERROR: E:\src\lib\sshutil\ssheloop\win32\ssheloop.c:1597 SshEventLoop (function name unavailable) Assertion failed: ssh_adt_num_objects(ssh_eloop_events) < 64

No doubt, proper error handling techniques have not been implemented for the SshEventLoop which ultimately causes the crash.

This results in a Denial of Service against the service in question.

  1. Vendor Status: Informed, Contacted.

  2. Fix: official fix will be available soon.

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