Bugtraq mailing list archives
Re: TCP SYN probe detection tool available
From: brian () saturn net (Brian Mitchell)
Date: Thu, 16 May 1996 12:49:50 -0400
On Thu, 16 May 1996, Henri Karrenbeld wrote:
I am afraid I do not read other security lists besides this one (I glance at Linux-alert and Linux-security occasionally when linux.dev.* mentions something)And of course stuff like cert-advisory, but in none of these have I seen what actually can be done with SYN packets... Could someone explain this?
Services can be probed for. Let's take 2 short examples: Attacker sends a syn packet to port 23 (telnet) There is no server on that port, so the server sends back a rst|syn sequence (acknowledging the syn, and tearing down the connection). In this case, nothing was listening, no logs will generally be generated. Now, an attacker does the same thing, but to say port 25 (smtp) There is a server on this port, the server sends back a ack|syn sequence The bad guy now knows there is something on the port, but because the three way handshake has not been completed it is not logged, the bad guy can then send a rst tearing down the connection, since he has the information he is after. I think some time ago a detailed post was made to this list describing the various ways a stealth scanner could be implemented, although i'm not 100% sure. Brian Mitchell brian () saturn net World Wide Web http://www.saturn.net/~brian "I never give them hell. I just tell the truth and they think it's hell" - H. Truman
Current thread:
- Re: SunOS 4.1.4 fingerd, (continued)
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- Re: SunOS 4.1.4 fingerd Craig Raskin (May 17)
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- CERT Vendor-Initiated Bulletin VB-96.06 - FreeBSD CERT Bulletin (May 20)
- Re: SunOS 4.1.4 fingerd invalid opcode (May 16)
- Re: TCP SYN probe detection tool available Henri Karrenbeld (May 16)
- Re: TCP SYN probe detection tool available Brian Mitchell (May 16)
- Re: TCP SYN probe detection tool available Mike Neuman (May 16)
- Re: TCP SYN probe detection tool available Darren Reed (May 26)
- Re: TCP SYN probe detection tool available JaDe (May 16)