snmpsize.py

#!/usr/bin/env python

#
# A rudimentary snmpwalk-like with scapy. Useful to choose a good
# OID to use during a SNMP reflected amplification DDos attack
#
# Usage: ./snmpsize.py 1.2.3.4 public 1.3.6.1.2.1 v1
#
# http://www.nothink.org
#

import signal,sys

# Change log level to suppress annoying IPv6 error
import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)

# Import scapy
try:
    from scapy.all import *
except:
    print "install scapy"
    print "http://www.secdev.org/projects/scapy/"

# Turn down the verbosity of scapy
conf.verb = 0

def signal_handler(signum,frame):
    global interrupted
    interrupted = True

def sendRequest(target,community,oid_prefix,version):

    nextoid = oid_prefix

    # best choices!
    best_oid = ''
    best_size = 0

    while True:

        p = IP(dst=target)/UDP(sport=161,dport=161)/SNMP(version=version,community=community,PDU=SNMPnext(varbindlist=[SNMPvarbind(oid=ASN1_OID(nextoid))]))

        #p.show()
        r = sr1(p)

        if r:
            # size
            rle = r.len

            # next oid
            oid = r[SNMPvarbind].oid.val

            if oid.startswith(oid_prefix):
                print oid + "\t" + str(rle) + " bytes"

                if int(rle) > best_size:
                    best_size = int(rle)
                    best_oid = oid

            else:
                print "\n\nbest choices: %s %s bytes\n" % (best_oid,str(best_size))
                break

            nextoid = oid

if __name__ == "__main__":

    if len(sys.argv) <= 4:
        print "Usage %s 1.2.3.4 public 1.3.6.1.2.1 v1" % sys.argv[0]
        sys.exit(1)

    try:
        sendRequest(sys.argv[1],sys.argv[2],sys.argv[3],sys.argv[4])

    except KeyboardInterrupt:
        print "Exit..."
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