Package: kea-ctrl-agent Version: 2.2.0-5 Severity: normal Tags: security X-Debbugs-Cc: andreas.hasen...@canonical.com, par...@debian.org, Debian Security Team <t...@security.debian.org>
Forwarded from: https://bugs.launchpad.net/ubuntu/+source/isc-kea/+bug/2007312 Originally reported by: Andreas Hasenack <andreas.hasen...@canonical.com> WIP fix: https://code.launchpad.net/~ahasenack/ubuntu/+source/isc-kea/+git/isc-kea/+merge/439352 Follows copypaste of the original bug as reported by Andreas. --- The kea-ctrl-agent package, when installed, starts a daemon (kea-ctrl-agent) that by default listens on 127.0.0.1:8000. It responds to commands like "shutdown", "config-get", and many others[1][2]. What's problematic is that these commands are accepted without authentication. Anyone on the localhost system can: a) shutdown a kea daemon: ubuntu@j-kea:~$ pidof kea-dhcp4 2884 ubuntu@j-kea:~$ curl -X POST -H "Content-Type: application/json" -d '{ "command": "shutdown", "service": [ "dhcp4" ] }' http://localhost:8000/ [ { "result": 0, "text": "Shutting down." } ]ubuntu@j-kea:~$ ubuntu@j-kea:~$ pidof kea-dhcp4 ubuntu@j-kea:~$ b) read the config file (in this example, I made the config file 0640 root:_kea so the ubuntu user cannot read it): ubuntu@andreas-isc-kea-server:~$ cat /etc/kea/kea-dhcp4.conf cat: /etc/kea/kea-dhcp4.conf: Permission denied ubuntu@andreas-isc-kea-server:~$ curl -X POST -H "Content-Type: application/json" -d '{ "command": "config-get", "service": [ "dhcp4" ] }' http://localhost:8000/| grep secret % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 4049 100 3998 100 51 134k 1751 --:--:-- --:--:-- --:--:-- 136k [ { "arguments": { "Dhcp4": { "authoritative": false, "boot-file-name": "", "calculate-tee-times": false, "config-control": { "config-databases": [ { "name": "kea", "password": "keasecret", .... The same could be done via the unix sockets, but the permissions there are not world writable, so this is avoided: $ ls -la /tmp/kea*socket srwxr-xr-x 1 _kea _kea 0 Feb 14 19:13 /tmp/kea-ddns-ctrl-socket srwxr-xr-x 1 _kea _kea 0 Feb 14 19:14 /tmp/kea4-ctrl-socket srwxr-xr-x 1 _kea _kea 0 Feb 14 19:13 /tmp/kea6-ctrl-socket One course of action is to disable listening on 127.0.0.1:8000 via the config file: /etc/kea/kea-ctrl-agent.conf: "Control-agent": { "http-host": "127.0.0.1", // If enabling HA and multi-threading, the 8000 port is used by the HA // hook library http listener. When using HA hook library with // multi-threading to function, make sure the port used by dedicated // listener is different (e.g. 8001) than the one used by CA. Note // the commands should still be sent via CA. The dedicated listener // is specifically for HA updates only. "http-port": 8000, (...) Or maybe setup authentication with a user created in postinst for this purpose, with a random password. The documentation[3], in the end of section 7.2, lists a mechanism to include username and password from an external file, so we don't have to adjust the permissions of kea-ctrl.agent.conf because of this. Finally, there is also a question about what to do on upgrades from systems that have this unprotected open port. 1. https://kea.readthedocs.io/en/kea-2.2.0/arm/ctrl-channel.html#commands-supported-by-both-the-dhcpv4-and-dhcpv6-servers 2. https://kea.readthedocs.io/en/kea-2.2.0/arm/ctrl-channel.html#commands-supported-by-the-d2-server 3. https://kea.readthedocs.io/en/kea-2.2.0/arm/agent.html#configuration
