Thanks.  I'll give that a try.

On 1/30/20 1:49 PM, Jack Craig wrote:
wireshark -> tcpdump on dst=port# src = all
??


On Thu, Jan 30, 2020 at 1:13 PM Michael Eager <ea...@eagercon.com <mailto:ea...@eagercon.com>> wrote:

    When I look at /var/log/secure or run journalctl on my workstation, I
    see failed SSH login attempts from a variety of IP addresses.  The
    attempts are every 3-12 minutes.

    /etc/ssh/sshd_config contains:
    PasswordAuthentication no

    The workstation is on a LAN behind an EdgeRouter firewall.  No Internet-
    accessible ports are forwarded to the workstation.  The LAN has a
    variety of servers, NAS boxes, WiFi access points, WiFi-connected
    laptops, etc.

    A typical /var/log/secure entry looks like this:
    Jan 30 12:43:50 redwood sshd[21228]: Invalid user jackiehulu from
    124.204.36.138 port 37394
    Jan 30 12:43:51 redwood sshd[21228]: Received disconnect from
    124.204.36.138 port 37394:11: Bye Bye [preauth]
    Jan 30 12:43:51 redwood sshd[21228]: Disconnected from invalid user
    jackiehulu 124.204.36.138 port 37394 [preauth]

    The corresponding journalctl is:
    Jan 30 12:43:51 redwood.eagercon.com <http://redwood.eagercon.com>
    audit[21228]: USER_ERR pid=21228
    uid=0 auid=4294967295 ses=4294967295
    subj=system_u:system_r:sshd_t:s0-s0:c0.c1023 msg='op=PAM:bad_ident
    grantors=? acct="?" exe="/usr/sbin/sshd" hostname=124.204.36.138
    addr=124.204.36.138 terminal=ssh res=failed'

    I'm assuming that something on the network has been compromised,
    allowing SSH login attempts on the LAN.  Other than turning off
    each server/AP/laptop/etc, one at a time, to find when the accesses
    stop, is there any way to find out where the SSH attempt is coming from?

    -- Mike Eager
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--
Michael Eager    ea...@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306
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