Hi Jochen, Jochen Bern wrote on Thu, Sep 09, 2021 at 08:28:27PM +0200: > What you could ask for *here* is that OpenSSH stops supporting SendEnv / > AcceptEnv altogether - but I have a hunch that you'll need a much more > convincing case to get *that* thermonuclear solution. I realize you may not be serious about this - but just in case someone thinks you are: that is hardly a solution, and much less a "thermonuclear" one, because some operating systems and operating system distributions have been known at various times in the past for patching features back in after said features had been removed from upstream software for security reasons. Besides, passing environment variables may occasionally be a useful feature in unusual situations for very experienced users who know what they are doing, especially in configuration stanzas where both the client host and the server host are tightly defined. Needless to say, passing LC_* is usually *not* useful because defining it statically on both sides is usually simpler and more robust. But *other* variables may be worth passing in special configurations. Passing variables by default, even for users who may have no idea what is happening and what the security implications are, and *for all hosts*, certainly doesn't look like a particularly smart idea to me personally. As i said earlier, OpenSSH already makes a pretty strong statement by not only documenting that this feature is off by default (except for TERM) but also by not even listing it in the "ssh_config" and "sshd_config" example configuration files, which list various other options that users are more likely to need knowing about. I believe i said this before, but it seems people missed it: What is discussed here has security implications. Specifically, if the shell on the server uses a locale that does not match the mode the client terminal or terminal emulator is using, the client is susceptible to terminal state corruption attacks that can be triggered by remote unprivileged users, for example by creating files with crafted, malicious file names in /tmp/ and hoping the user logging in remotely will issue a command like "ls /tmp/". Depending on the client terminal configuration, such attacks can leverage a wide variety of terminal features - for example, freezing the client terminal (DOS attack) is often trivial, usually in multiple different ways, but more elaborate attacks like simulating or falsifying output or in the worst case, injecting bogus, hostile keystrokes into the client terminal might sometimes also be possible. Neither passing nor not passing these variables does anything to improve security. You are passing *the wrong data*. What matters is the mode the client terminal is running in. That is not the same as the locale(1) set in the shell running inside that terminal. On top of that, as you observed, passing that irrelevant locale to the server by no means assures that the remote host will accept it and/or even supports it. Again, i don't think a technical solution exists. What matters is educating users (1) what terminal modes are and why they matter and (2) that using SSH safely requires considering the terminal mode on the client side, and the locale on the remote side, before connecting. I very much doubt that trying to invent some kind of magical setting will help with that - quite apart from the fact that magic doesn't work in the first place. Yours, Ingo _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
