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
}
}
I've gotten over 100 INVITEs or REGISTERs .
Also nft changes the hex to decimal. Here's the input:
# INVITE ascii = 0x494e56495445 hex , 48 (6 * 8 ) bits long
# REGISTER ascii = 52 45 47 49 53 54 45 52 , 64 ( 8 * 8 ) bits long
chain raw {
type filter hook prerouting priority raw; policy accept;
udp dport 5060 @th,184,48 0x494e56495445 counter
packets 0 bytes 0
udp dport 5060 @th,184,64 0x5245474953544552 counter
}
I'd suggest nft should leave it in hex.
Here's the tcpdump output
0x0000: 001f 1249 0acc 5254 00e7 8e30 0800 45a0 ...I..RT...0..E.
0x0010: 03e1 0000 4000 4011 01dd 511d d3c4 d461 ....@.@...Q....a
0x0020: 3b4c 13c4 13c4 03cd 386e 494e 5649 5445 ;L......8nINVITE
INVITE starts at bit 337 (128 * 2 ) + ( 5 * 16 ) +1, but this is zero
based, so use 336, correct?
As I read your response, it's not the offset from the beginning, but
after the UDP header,
so 336 - 120 , or 216. (BTW, I always thought the UDP header was 160 bits.)
udp dport 5060 @th,216,48 0x494e56495445 counter
Sorry for being so long-winded. I appreciate your help in sorting this out.
sean
