SNMP DDoS: the vulnerability you might not know you have

Blake Dunlap ikiris at
Wed Jul 31 14:57:32 UTC 2013

This looks like more a security issue with the devices, not border security

If you're seeing replies of that size, it means the devices themselves are
set up to allow public queries of their information (not secured by even
keys), which no one should be comfortable with. People should never be
leaving the public access snmp strings on devices even if they are
internal. Edge blocking just masks the real issue.


On Tue, Jul 30, 2013 at 11:25 PM, bottiger <bottiger10 at> wrote:

> Before you skim past this email because you already read the Prolexic
> report on it or some other article on the internet, there are 2
> disturbing properties that I haven't found anywhere else online.
> 1) After sending abuse emails to many networks, we received many angry
> replies that they monitored their traffic for days without seeing
> anything (even as we were being attacked) and that their IPs were
> spoofed and would block us for spamming them.
> What we discovered was that their firewalls/routers/gateways coming
> from vendors like Cisco and SonicWall apparently didn't record SNMP
> traffic going in or out of themselves. We confirmed this multiple
> times by running a query to an IP that was claimed to be clean and
> watching the response come 10-60 seconds later because the device was
> being so heavily abused.
> 2) SNMP reflection offers the largest amplification factor by far,
> even surpassing DNS, Chargen, or NTP by a wide margin. I have tested a
> 68 byte query and received responses of up to 30,000 to 60,000 bytes.
> The trick is to use GetBulkRequest to start enumerating from the first
> OID and setting max repetitions to a large number. This is contrary to
> the other articles online which suggest a much smaller amplification
> factor with other queries.
> This protocol is also prevalent in many devices ranging from routers
> to printers.
> To solve this problem you should block SNMP traffic coming from
> outside your network and whitelist outside IPs that require it.

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