Purpose of spoofed packets ???

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1

We recently got an abuse report of an IP address in our net range. However, that IP address isn't in use in our networks and the covering network is null routed, so no return traffic is possible. We have external BGP monitoring, so unless something very tricky is going on, we don't have part of our prefix hijacked.

I assume the source address was spoofed, but this leads to my question. Since the person that submitted the report didn't mention a high packet rate (it was on ssh port 22), it doesn't look like some sort of SYN attack, but any OS fingerprinting or doorknob twisting wouldn't be useful from the attacker if the traffic doesn't return to them, so what gives?

BTW, we are in the ARIN region, the report came out of the RIPE region.

2

Highly-distributed, pseudo-randomly spoofed SYN-flood happened to momentarily use one of your addresses as a source. pps/source will be relatively low, whilst aggregate at the target will be relatively high.

Another very real possibility is that the person or thing which sent you the abuse email doesn't know what he's/it's talking about.

;>

3

Interesting... we had exactly the same an hour ago. That IP was definitely nullrouted for >1 week...

Matthew Huff:

4

Is it possible that they are getting return traffic and it's just a localized activity? The attacker could announce that prefix directly to the target network in an IXP peering session (maybe with no-export) so that it wouldn't set off your bgpmon. I guess that would make more sense if they were doing email spamming instead of ssh though.

-Laszlo

5

Another very real possibility is that the person or thing which sent
you
the abuse email doesn't know what he's/it's talking about.

Was my first thought, but wanted to run this by everyone in case I was
missing something obvious.

6

Either the reporter doesn't know what they're talking about (common enough) or someone is scanning for open ssh ports, hiding their real IP address by burying it in a host of faked source addresses. That's a standard option on some of the stealthier port scanners, IIRC.

Cheers,
  Steve

7

Nmap has an option to "hide" your real IP among either a provides or IP
list of IP addresses.

" D *<**decoy1**>*[,*<**decoy2**>*][,ME][,...] (Cloak a scan with decoys)

Causes a decoy scan to be performed, which makes it appear to the remote
host that the host(s) you specify as decoys are scanning the target network
too. Thus their IDS might report 5–10 port scans from unique IP addresses,
but they won't know which IP was scanning them and which were innocent
decoys. While this can be defeated through router path tracing,
response-dropping, and other active mechanisms, it is generally an
effective technique for hiding your IP address."

http://nmap.org/book/man-bypass-firewalls-ids.html

We recently got an abuse report of an IP address in our net range.

However, that IP address isn't in use in our networks and the covering
network is null routed, so no return traffic is possible. We have external
BGP monitoring, so unless something very tricky is going on, we don't have
part of our prefix hijacked.

I assume the source address was spoofed, but this leads to my question.

Since the person that submitted the report didn't mention a high packet
rate (it was on ssh port 22), it doesn't look like some sort of SYN attack,
but any OS fingerprinting or doorknob twisting wouldn't be useful from the
attacker if the traffic doesn't return to them, so what gives?

BTW, we are in the ARIN region, the report came out of the RIPE region.

Either the reporter doesn't know what they're talking about (common enough)
or someone is scanning for open ssh ports, hiding their real IP address by
burying it in a host of faked source addresses. That's a standard option on
some of the stealthier port scanners, IIRC.

Cheers,
  Steve

8

Nmap has an option to "hide" your real IP among either a provides or IP
list of IP addresses.

" D *<**decoy1**>*[,*<**decoy2**>*][,ME][,...] (Cloak a scan with decoys)

Causes a decoy scan to be performed, which makes it appear to the remote
host that the host(s) you specify as decoys are scanning the target
network
too. Thus their IDS might report 5­10 port scans from unique IP addresses,
but they won't know which IP was scanning them and which were innocent
decoys. While this can be defeated through router path tracing,
response-dropping, and other active mechanisms, it is generally an
effective technique for hiding your IP address."

Firewall/IDS Evasion and Spoofing | Nmap Network Scanning

Thanks. I thought it was something obvious that I was missing. This makes
sense.

9

One more outré purpose for spoofing SIPs is to have you blacklist/nullroute someone, effectively enlisting you to cause a DOS.

--p