Aaron,
 
Based on the information you have provided, its hard to tell which specific
plugin might be causing a CPU spike on the router.
 
Few questions :
 
- Is SSH enabled on the router?. If so, which version.
- Is "Do not log in with user accounts not specified in the policy" in
Global variable settings disabled for the scan?
- During the scan, could you tell by looking at the pcaps which ports Nessus
is connecting to and what specific requests it is sending to the router
which causes a noticeable CPU spike?
 
One way to identify the plugin causing a CPU spike, would be to enable "Log
details of the scan on the server" and set "Number of checks in parallel" to
1, this will ensure plugins are run sequentially. Once you have this setup,
tail -f nessusd.messages and monitor the router for any CPU spikes.  
 
- Mehul



  _____  

From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Aaron Weissenfluh
Sent: Tuesday, July 15, 2008 3:31 PM
To: [email protected]
Subject: Cisco tty CPU Spike


All,
I've run into an issue where I've seen the cpu utilization spike
specifically relating to the TTY Daemon on a router when scanned by Nessus.
The cpu will initially spike up to 15% then spike up to 40% and will stay
there following a simple "safe-checks" scan.  The cpu will not drop until I
disconnect the tty com.  I have configured nessus to tcp scan ports 1-65535
and I've got all the default plugins enabled but with safe checks on and
really nothing that different from a default scan enabled.  Not that it's
causing a huge issue - just working to figure out what specific plugin is
causing the actual problem.  Anyone seen anything like this before?

Here's the specific information about the router and scanner if that helps:
Cisco 2821 Router
Version 12.4 (13r) T Release fc1

sh proc cpu sort (output):
CPU utilization for five seconds: 38%/0%; one minute: 41%; five minutes: 42%

 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process 
  70   8731285401349143954        647 38.23% 41.10% 42.18%   1 TTY Daemon

  38    15980516 136215965        117  0.08%  0.07%  0.08%   0 TTY
Background   

Nessus 3.2.1 on SuSE, plugins updated daily.

Thanks,
A


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