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+++ This bug was initially created as a clone of Bug #1791677 +++

Description of problem:

Upstream libslirp has disabled emulation of the tcp programs like ftp/IRC etc. in user-mode SLiRP networking since v4.1.0.

 ->  https://gitlab.freedesktop.org/slirp/libslirp/commit/07c2a44b67e219ac14207f7a1b33704e1312cf91

   emu: disable by default

tcp_emu() is known to have caused several CVEs, and not useful today in most cases.

https://nvd.nist.gov/vuln/detail/CVE-2019-6778
https://nvd.nist.gov/vuln/detail/CVE-2019-9824

The feature can be still enabled by setting SlirpConfig.enable_emu to
true.

* Please include this patch in the qemu-kvm package versions of RHEL too.

* It'll probably be better to disable user-mode SLiRP networking itself in qemu-kvm.

  ie. compile qemu-kvm package with '--disable-slirp' configure option.

Has successful reproduced it with qemu-kvm-1.5.3-173.el7 and Verified it with fix version qemu-kvm-1.5.3-174.el7. 

Steps:
1. boot up guest with "/usr/libexec/qemu-kvm -enable-kvm -nographic -m 2048 -net user,hostfwd=tcp::2222-:22 -net nic /root/rhel78-64-virtio.qcow2"
2. nc -l 127.0.0.1 113 on host
3. run on guest
nc -C 10.0.2.2 113 
1234    ,   4321 

Results:

With qemu-kvm-1.5.3-173.el7:

# nc -l 127.0.0.1 113
1234,4321

With qemu-kvm-1.5.3-174.el7:
# nc -l 127.0.0.1 113
1234    ,   4321

Base on above, set it to VERIFIED. Thanks all

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Low: qemu-kvm security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2020:3906