Suricata is a network Intrusion Detection System, Intrusion Prevention System and Network Security Monitoring engine developed by the OISF and the Suricata community.
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Eric Leblond 5f224f87d1 reject: update computation of seq and ack
We have follow TCP RFC (http://tools.ietf.org/html/rfc793#section-3.4).
There is two cases depending on wether the original packet contains a
ACK.
If packet has no ACK, the RST seq number is 0 and the ACK is built the
standard way.
If packet has a ACK, the seq of the RST packet is equal to the ACK of
incoming packet and the ACK is build using packet sequence number and
size of the data.

Regarding standard Ack number, it is computed using seq number of captured
packet added to packet length. Finally 1 is added so we respect the
RFC:
    If the ACK control bit is set this field contains the value of the
    next sequence number the sender of the segment is expecting to
    receive.  Once a connection is established this is always sent.

With this patch we have some correct results. With the following rule:
    reject ssh any any -> 192.168.56.3 any (msg:"no SSH  way"; sid:3; rev:1;)
ssh connection to 192.168.56.3 is correctly resetted on client side.

But this is not perfect. If we have the following rule:
    reject tcp any any -> 192.168.56.3 22 (msg:"no way"; sid:2; rev:1;)
then the connection is not resetted on a standard ethernet network. But
if we introduce 20ms delay on packets, then it is correctly resetted.
This is explained when looking at the network trace. The reset is sent
as answer to the SYN packet and it is emitted after the SYN ACK from
server because the exchange is really fast. So this is discarded by the
client OS which has already seen a ACK for the same sequence number.

This should fix #895.
12 years ago
benches
contrib
doc
m4
qa coccinelle: implement parallel check 12 years ago
rules Add decoder event rule for tls event "invalid_ssl_record", which will now be available "app-layer-event:tls.invalid_ssl_record". 12 years ago
scripts
src reject: update computation of seq and ack 12 years ago
.gitignore
COPYING
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Makefile.am Use wget or curl to download ruleset. 12 years ago
Makefile.cvs
acsite.m4
autogen.sh
classification.config
config.rpath
configure.ac pcre: check for pcre_free_study, fall back to pcre_free if it unavailable 12 years ago
doxygen.cfg
mkinstalldirs
reference.config
suricata.yaml.in reject: use host-mode to set interface 12 years ago
threshold.config