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Cause: dhclient opened additional random port for listening
Consequence: Security applications reported issue.
Fix: Port are opened only if the DDNS functionality is used by dhclient.
Result: No additional port opened in case if DNS update is not in use.
Description of problem:
DHClient creates an additional listening port in addition to UDP 68 which seems to be a random registered port value.
How reproducible:
Install dhclient, start the service and perform a netstat -l -u -p and check each of the ports opened by dhclient.
Actual results:
In this example Opening 60964 port unnecessary :
# netstat -panl |grep dhcl
udp 0 0 0.0.0.0:60964 0.0.0.0:* 7594/dhclient
udp 0 0 0.0.0.0:68 0.0.0.0:* 7594/dhclient
Expected results:
It should open only 68 port :
udp 0 0 0.0.0.0:68 0.0.0.0:* 7594/dhclient
Additional info:
Additional Info:
https://bugzilla.redhat.com/show_bug.cgi?id=962950http://forums.debian.net/viewtopic.php?f=10&t=95273http://forums.debian.net/viewtopic.php?f=10&t=95273&p=495605#p495605
As described in bug #962950, comment #5 it's libdns (bind package) what opens these ports and that the only workaround I'm aware of is building dhcpd/dhclient without DDNS support which is most likely not what we want. I can reassign this to bind to further investigate whether it'd be possible to not open these ports in libdns during initialization.
Created attachment 1269039[details]
spawn dns ports on demand later
Simple fix delaying creation of those ports. I did not check for possible race conditions much, but it seems to fix the issue.
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, 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/RHBA-2018:0658