Debian 8: DLA-2087-1 Critical: Suricata TCP Evasion Issues

CVE-2019-18625

It was possible to bypass/evade any tcp based signature by faking a
closed TCP session using an evil server. After the TCP SYN packet, it
was possible to inject a RST ACK and a FIN ACK packet with a bad TCP
Timestamp option. The client would have ignored the RST ACK and the
FIN ACK packets because of the bad TCP Timestamp option.

CVE-2019-18792

It was possible to bypass/evade any tcp based signature by
overlapping a TCP segment with a fake FIN packet. The fake FIN packet
had to be injected just before the PUSH ACK packet we wanted to
bypass. The PUSH ACK packet (containing the data) would have been
ignored by Suricata because it would have overlapped the FIN packet
(the sequence and ack number are identical in the two packets). The
client would have ignored the fake FIN packet because the ACK flag
would not have been set.

For Debian 8 "Jessie", these problems have been fixed in version
2.0.7-2+deb8u5.