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Home » Hacking News » Remote DoS attack against SSH Secure Shell

Remote DoS attack against SSH Secure Shell

by phiber on March 16th, 2001 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:srclibsshutilssheloopwin32ssheloop.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.





Vendor Status:
Informed, Contacted.



Fix:
official fix will be available soon.





This vulnerability was discovered by USSR Labs.


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