Stealth Scans

This topic contains 6 replies, has 5 voices, and was last updated by  mrvore 6 years, 8 months ago.

  • Author
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  • #8307
     imij0607 
    Participant

    This might be the right place to ask this question…if not please let me know and I’ll redirect. 

    I’m wondering what kind of scan (hping, nmap, etc) would make it look like the firewall blocked traffic, but the host actually replied to the ping?…meaning the traffic was not dropped by firewall.

  • #52322
     dynamik 
    Participant

    I don’t think there’s a straight-forward answer to that. If that condition is possible anywhere, it’s going to depend greatly on the make and version of the firewall. You’d have to find some sort of glitch regarding checksums, payload contents, fragment reassembly, etc. Varying the ICMP type may be useful as well (i.e. timestamp instead of echo).

    Research network fuzzing, and then compare what gets through with what’s in the drop log.

  • #52323
     imij0607 
    Participant

    right – i definitely need to get a sniffer on that segment…it could be false positive via mis-config of appliances…

  • #52324
     rattis 
    Participant

    A ping will go through, if you’re not blocking ICMP.

  • #52325
     imij0607 
    Participant

    right – ping would go through but this is port 80 HTTP traffic…that much i know…
    technically the firewall is blocking port 80 inbound and outbound…soooo….
    lol =)

  • #52326
     dark_knight_baby 
    Participant

    hmmm stealth scans? why not muddying the waters of their log files? like use the Decoy functionality in nmap with matching spoofing of MAC and slowing down your timing….assuming you got target IPs you can do a ZOMBIE technique with Decoy….it will surely slowdown the guys who will try to trace the attack…

    just my 2 cents

  • #52327
     mrvore 
    Participant

    SYN Stealth Scan [-sS] in Nmap

    To initiate a TCP connection, the initiating system sends a SYN packet to
    the destination, which will respond with a SYN of its own, and an ACK, acknowledging
    the receipt of the first packet (these are combined into a single SYN/ACK
    packet). The first system then sends an ACK packet to acknowledge receipt of
    the SYN/ACK, and data transfer can then begin.
    SYN or Stealth scanning makes use of this procedure by sending a SYN packet
    and looking at the response. If SYN/ACK is sent back, the port is open and the
    remote end is trying to open a TCP connection. The scanner then sends an RSTto tear down the connection before it can be established fully; often preventing
    the connection attempt appearing in application logs. If the port is closed, an
    RST will be sent. If it is filtered, the SYN packet will have been dropped and
    no response will be sent. In this way, Nmap can detect three port states – open,
    closed and filtered. Filtered ports may require further probing since they could
    be subject to firewall rules which render them open to some IPs or conditions,
    and closed to others.
    Modern firewalls and Intrusion Detection Systems can detect SYN scans, but
    in combination with other features of Nmap, it is possible to create a virtually
    undetectable SYN scan by altering timing and other options.

    I hope this may shed some light on what you are looking for.

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