El 19/02/2019 a las 4:16, Russ Allbery escribió: > Unfortunately, I took a closer look, and it turns out that this command > was never safe. It also allows arbitrary code excution on the server > side if the client can write to $HOME. This is because: > > --config=FILE > This specifies an alternate config file than the default. This > is only relevant when --daemon is specified. The default is > /etc/rsyncd.conf unless the daemon is running over a remote > shell program and the remote user is not the super-user; in that > case the default is rsyncd.conf in the current directory > (typically $HOME). > > That behavior of loading rsyncd.conf from the current directory was the > piece I had missed before.
Well, in my case I had the following setting in rsyncd.conf: path = /backup/synology where path points to a different directory which is NOT $home nor doesn't permit to reach $home. So you cannot overwrite /home/synology/rsyncd.conf. Well... provided that "path" config is not affected by path traversal ("../../home/synology"). At least, what I understand from rsyncd.conf manual is that it shouldn't be possible: **path** This parameter specifies the directory in the daemon's filesystem to make available in this module. You must specify this parameter for each module in |rsyncd.conf|. At the same time, my /etc/rssh.conf has: user=synology:022:100000: # rsync, with no chroot So rssh shouldn't permit to use scp or other methods in order to overwrite rsyncd.conf. My setup seems safe (am I missing something?). > Presumably, this is exactly the behavior that Synology relies on, but this > means that if the client can write to this configuration file, it can just > include a pre-xfer exec setting in that rsyncd.conf file and run commands > on the server side. Not in my setup. > So, unfortunately we won't be able to fix Synology in a stable update, > since it was relying on insecure behavior. I'll continue with an update > to fix the libssh2 regression. I don't know how many people is using rssh (I guess not that many), but if we limit its use more, it will probably die (it will probably die in either case :-)). Cheers, -Román