An issue was discovered in Suricata 5.0.0. It is possible to
bypass/evade any tcp based signature by overlapping a TCP segment with a
fake FIN packet. The fake FIN packet is injected just before the PUSH
ACK packet we want to bypass. The PUSH ACK packet (containing the data)
will be ignored by Suricata because it overlaps the FIN packet (the
sequence and ack number are identical in the two packets). The client
will ignore the fake FIN packet because the ACK flag is not set. Both
linux and windows clients are ignoring the injected packet.
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
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