SCAN/SCAN_SSH_Brute_Force:
alert tcp $EXTERNAL_NET any -> $HOME_NET 22 (msg: "BLEEDING-EDGE
Potential SSH Scan"; flags: S; flowbits: set,ssh.brute.attempt;
threshold: type threshold, track by_src, count 5, seconds 120;
classtype: suspicious-login; sid: 2001219; rev:10; )
We've tweaked this one to be near perfect. We are setting the
ssh.brute.attempt, but the other sigs that used to use it were removed.
So we could take that out, but it'll surely be useful somewhere down the
line.
This is in the SCAN ruleset on bleeding.
Let us know how the threshold in this one affects your net, being larger
than average.
Matt
Paul Schmehl wrote:
Does anyone have one?
I put together a very simple one to catch *outgoing* evil, but I'm
wondering if anyone has packet captures that would help with content
definitions.
Here's the rule I wrote:
# New rule for catching ssh brute-force attacks
alert tcp $HOME_NET any -> any 22 (msg:"SSH Brute-Force attack";
threshold: type both, track by_src, count 2000, seconds 60;
classtype:trojan-activity; sid:1000281; rev:2;)
It's catching some legitimate sessions, so I'l probably need to raise
the threshold more, but I'm wondering if there's a packet capture that
has something unique the rule could trigger on.
Paul Schmehl (pauls@utdallas.edu)
Adjunct Information Security Officer
University of Texas at Dallas
AVIEN Founding Member
http://www.utdallas.edu/ir/security/
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