[Bug 1176046] Re: isc-dhcp dhclient listens on extra random ports

[Eric Desrochers]

Sound similar to debian bug : https://bugs.debian.org/cgi-
bin/bugreport.cgi?bug=712503

The situation doesn't occur on Xenial (16.04 LTS), but present in Trusty
(14.04) as a fix has been first introduce in Ubuntu with version : isc-
dhcp (4.3.3-2)

Trusty : 
#netstat -tulp | grep -i dhclient
udp        0      0 *:bootpc                *:*                                 23402/dhclient  
udp        0      0 *:bootpc                *:*                                 1589/dhclient   
udp        0      0 *:33749                 *:*                                 1589/dhclient   
udp        0      0 *:11662                 *:*                                 23402/dhclient  
udp6       0      0 [::]:7082               [::]:*                              1589/dhclient   
udp6       0      0 [::]:12668              [::]:*                              23402/dhclient  


Xenial:
# netstat -tulp | grep -i dhclient
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
udp        0      0 *:bootpc                *:*                                 142/dhclient    


# changelog
isc-dhcp (4.3.3-2) unstable; urgency=medium
...
 ===> * Disable NSUPDATE (closes: #712503). <==
...

** Bug watch added: Debian Bug tracker #712503
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=712503

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https://bugs.launchpad.net/bugs/1176046

Title:
  isc-dhcp dhclient listens on extra random ports

Status in isc-dhcp package in Ubuntu:
  Triaged

Bug description:
  Ubuntu 13.04 Server 64-bit.  Fresh install.  Only one network adapter.

  dhclient process is listening on two randomly chosen udp ports in
  addition to the usual port 68.  This appears to be a bug in the
  discovery code for probing information on interfaces in the system.

  Initial research of the code also suggested omapi, but adding omapi
  port 9999 to /etc/dhcp/dhclient.conf only opened a forth port with the
  two random udp ports still enabled.

  Version of included distro dhclient was 4.2.4.  I also tested with the
  latest isc-dhclient-4.2.5-P1 and got the same results.

  Debian has the same bug:
  http://forums.debian.net/viewtopic.php?f=10&t=95273&p=495605#p495605

  One impact of these random ports is that security hardening becomes
  more difficult.  The purpose of these random ports and security
  implications are unknown.

  
  Example netstat -lnp  output:

  udp        0      0 0.0.0.0:21117           0.0.0.0:*                           2659/dhclient   
  udp        0      0 0.0.0.0:68              0.0.0.0:*                           2659/dhclient   
  udp6       0      0 :::45664                :::*                                2659/dhclient

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