** Description changed: [Impact] In trusty, there is only 1 version of dhclient, including #define NSUPDATE, which introduce DDNS functionnality. The DDNS functionnality, generate 2 random extra ports between 1024-65535. Impact reported by users : "One impact of these random ports is that security hardening becomes more difficult. The purpose of these random ports and security implications are unknown." "We have software that was using one of the lower udp ports but it happened to collide with dhclient which seems to allocate 2 random ports." - There is a randomization mechanism in libdns that prevent dhclient to take the sysctl values into account (net.ipv4.ip_local_port_range & net.ipv4.ip_local_reserved_ports) to workaround this, and after discussion isc-dhcp upstream doesn't want to rely on kernel for randomization. - - There is no realtime configuration to disable the feature or workaround this. The only possible way is at compile time. + There is a randomization mechanism in libdns that prevent dhclient to + take the sysctl values into account (net.ipv4.ip_local_port_range & + net.ipv4.ip_local_reserved_ports) to workaround this, and after + discussion isc-dhcp upstream doesn't want to rely on kernel for + randomization. + + There is no realtime configuration to disable the feature or workaround + this. The only possible way is at compile time. I also talk with upstream maintainers, and there is no way they will accept to reduce the range (1024-65535) for security reason. Reducing the port range may facilitate the spoofing. Xenial has separated dhclient in two packages : isc-dhcp-client pkg : dhclient with DDNS functionality disabled (no random extra ports) isc-dhcp-client-ddns : dhclient with DDNS functionality enabled (with random extra ports) The goal here is to reproduce the same situation in Trusty, for this bug to be less painful for at least users that doesn't require DDNS functionnality. [Test Case] Run a Trusty image with following package : isc-dhcp-client isc-dhcp-common ``` dhclient 1110 root 6u IPv4 11535 0t0 UDP *:bootpc dhclient 1110 root 20u IPv4 11516 0t0 UDP *:64589 # <----------- extra random port dhclient 1110 root 21u IPv6 11517 0t0 UDP *:7749 # <----------- extra random port ``` + [Regression Potential] - [Regression Potential] + I did the split such that Trusty users will automatically get "isc-dhcp- + client-ddns" installed but users bothered by this bug will have the + option to switch to "isc-dhcp-client-noddns". - * none expected - - I did the split such that users will automatically get isc-dhcp-client-ddns installed but users bothered by this bug then will have the option to switch to the one without it by uninstalling (isc-dhcp-client-ddns), - so existing Trusty users can continue to use this DDNS functionality after the SRU without any necessary intervention. + Existing Trusty users can continue to use this DDNS functionality after + the SRU without any necessary intervention. With isc-dhcp-client-ddns : dhclient 1110 root 6u IPv4 11535 0t0 UDP *:bootpc dhclient 1110 root 20u IPv4 11516 0t0 UDP *:64589 # <----------- extra random port dhclient 1110 root 21u IPv6 11517 0t0 UDP *:7749 # <----------- extra random port Without isc-dhcp-client-ddns : dhclient 1110 root 6u IPv4 11535 0t0 UDP *:bootpc Note that this is how Xenial does it. + Caribou and I, slashd, have also tested a couple of release upgrade from Trusty to Xenial with both scenarios : + 1 - Trusty upgrade to Xenial with "isc-dhcp-client-ddns" + 2- Trusty upgrade to Xenial with "isc-dhcp-client-noddns" + + and both scenarios worked as expected for caribou and I. (See comment + #42) + [Other Info] - - * See : https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1176046/comments/19 to look at my discussion with rbasak on if that approach would be acceptable for SRU. + + * See : https://bugs.launchpad.net/ubuntu/+source/isc- + dhcp/+bug/1176046/comments/19 to look at my discussion with rbasak on if + that approach would be acceptable for SRU. [Original 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
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1176046 Title: isc-dhcp dhclient listens on extra random ports To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1176046/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
