On 9/27/20 4:59 PM, Pablo Neira Ayuso wrote:
On Sun, Sep 27, 2020 at 11:42:08AM -0400, sean darcy wrote:
On 9/27/20 10:03 AM, Pablo Neira Ayuso wrote:
On Sun, Sep 27, 2020 at 03:54:47PM +0200, Pablo Neira Ayuso wrote:
On Sat, Sep 26, 2020 at 03:10:24PM -0400, sean darcy wrote:
nftables-0.9.6
I'm running a VOIP server. There are lots of script kiddies who will bang
away with 10/sec SIP INVITES or REGISTERS .
In iptables you can match on the string:
-A SIP -i eth0 -p udp -m udp --dport 5060 -m string --string "INVITE"
--algo bm --from 23 --to 28 -m comment --comment "Catch SIP INVITEs" -j
SIPINVITE
-A SIP -i eth0 -p udp -m udp --dport 5060 -m string --string "REGISTER"
--algo bm --from 23 --to 30 -m comment --comment "Catch SIP REGISTERs" -j
SIPREGISTER
I'm looking at RAW to do the same:
nft add rule x y udp dport 5060 @th,64,48 0x494e56495445 counter
@th => transport header
64 => from bit number 64 (8 bytes after the UDP header)
48 => extract 48 bits (6 bytes for INVITE)
@th,offset,length
where offset and length are expressed in bits.
Thanks for the response.
I corrected it , but it didn't work:
nft list chain filter raw
table ip filter {
chain raw {
type filter hook prerouting priority raw; policy accept;
udp dport 5060 @th,184,48 80600803923013 counter packets 0 bytes 0
udp dport 5060 @th,184,64 5928222864759342418 counter packets 0 bytes 0
This should be:
@th,64,48 0x494e56495445 counter
you specify offset to 184, that does not look fine.
If you want to match INVITE right after the UDP header, in the initial
6 bytes of the payload, then offset is 64 bits give that UDP header is
8 bytes (64 bits).
Note that @th specifies that the offset is relative to the transport
header offset. Similarly, @nh specifies the offset relative to the
network header.
I tried it here with nc -u and sending the string INVITE and it works
fine.
It's working. Thanks for all the quick and responsive help.
For those who find this exchange, and are as clueless as I am about bit
counting network packets, and the differences between link layer,
network header, and transport header:
table ip filter {
chain raw {
type filter hook prerouting priority raw; policy accept;
udp dport 5060 @th,64,48 80600803923013 counter packets 221 bytes 162020
udp dport 5060 @th,64,64 5928222864759342418 counter packets 67 bytes
39671
udp dport 5060 @ll,336,48 80600803923013 counter packets 221 bytes 162020
udp dport 5060 @ll,336,64 5928222864759342418 counter packets 67 bytes
39671
udp dport 5060 @nh,224,48 80600803923013 counter packets 221 bytes
162020 drop
udp dport 5060 @nh,224,64 5928222864759342418 counter packets 67 bytes
39671 drop
}
}
I repeat my suggestion that "nft list" show the pattern to be matched in
hex, as it is in the command.
sean
