Snort mailing list archives
re: spp_stream4: TTL EVASION (reassemble) detection
From: Kevin Peuhkurinen <kevinp () routergod com>
Date: Fri, 20 Sep 2002 13:18:45 -0400
If you add "ttl_limit 0" to the end of your stream4 entry in snort.conf, it should silence those alerts.
The problem here is that when stream4 gets the first packet of a TCP connection, it captures the initial TTL value. Then, for every packet in that conversation where the TTL value is off by ttl_limit (which defaults to 5), it produces this alert. This is supposed to default TTL based evasion techniques. So, let us say that you have a persistent TCP connection and at some point a router goes down and the traffic starts going a different way with an extra 5 hops... this means that every single packet after this point is going to generate this alert.
Changing the ttl_limit to 0 will tell stream4 to not bother checking for ttl changes.
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Current thread:
- RE: spp_stream4: TTL EVASION (reassemble) detection McCammon, Keith (Sep 20)
- Re: spp_stream4: TTL EVASION (reassemble) detection Pedro Tedeschi (Sep 20)
- <Possible follow-ups>
- re: spp_stream4: TTL EVASION (reassemble) detection Kevin Peuhkurinen (Sep 20)