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OpenSSH: client bug CVE-2016-0777

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Re: OpenSSH: client bug CVE-2016-0777

#71
post #60
post #48

Earlier quoted context omitted.

https://github.com/openssh/openssh-portable/blob/e6c85f8889c... Here you go

Actually, I quickly generated a list of undocumented config options: http://sprunge.us/QDSE Edit: Fixed version http://sprunge.us/LVYB

I believe "kerberosauthentication" and "rhostsauthentication" are documented as well. I'd check the "official" OpenBSD man page instead of whatever you have on your system. Regardless, thanks.

Re: OpenSSH: client bug CVE-2016-0777

#72
post #59
post #57

Earlier quoted context omitted.

It's from the linked page.

Indeed. The page gives bad advise. If your config has `Host` blocks, like often in people's personal configs, or if you have a `Match` block, the new directive only applies to the last of those blocks in the config file.

Sufficient to place it at the top of ~/.ssh/config? Or does it also need a block header of its own, like:

    Host *
    UseRoaming no

Re: OpenSSH: client bug CVE-2016-0777

#73

Does it strike anyone else as bizarre / poor form for an experimental feature to be enabled by default in OpenSSH, which is normally very conservative with option defaults?

It just sounds like a big code-base fuckup. They more or less admit it: "Server side was disabled/gutted for years already, but this aspect was surprisingly forgotten." Sounds like this was put in at one time, forgotten about, and the code lingered for a long time until someone pointed it out. SSH as a protocol is pretty crazy. Everyone loves it, but its a lot of things in one, which ironically goes against the unix…

Pretty sure this is OpenSSH only. PuTTY and SecureCRT, at least, are reported not to be affected.

Re: OpenSSH: client bug CVE-2016-0777

#74

Does it strike anyone else as bizarre / poor form for an experimental feature to be enabled by default in OpenSSH, which is normally very conservative with option defaults?

It just sounds like a big code-base fuckup. They more or less admit it: "Server side was disabled/gutted for years already, but this aspect was surprisingly forgotten." Sounds like this was put in at one time, forgotten about, and the code lingered for a long time until someone pointed it out. SSH as a protocol is pretty crazy. Everyone loves it, but its a lot of things in one, which ironically goes against the unix…

Given that this exploit happens during capability negotiation (or whatever SSH calls that part of the protocol), it also cannot be mitigated via pledge[2], which is where OpenBSD has been focusing a lot of attention. This is an unusual stumble for the OpenBSD team. Client-side privsep support, if such a thing existed, might mitigate attacks like this. As it stands protecting against exploits of this type wasn't even on the hardening roadmap.

http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/...

Re: OpenSSH: client bug CVE-2016-0777

#75
post #60

Earlier quoted context omitted.

Actually, I quickly generated a list of undocumented config options: http://sprunge.us/QDSE Edit: Fixed version http://sprunge.us/LVYB

I believe "kerberosauthentication" and "rhostsauthentication" are documented as well. I'd check the "official" OpenBSD man page instead of whatever you have on your system. Regardless, thanks.

Neither of those are mentioned on the latest manpage from git.

Re: OpenSSH: client bug CVE-2016-0777

#76

Earlier quoted context omitted.

Is there any way to update openssh on my side, without waiting to apple ? Is this enough ? https://mochtu.de/2015/01/07/updating-openssh-on-mac-os-x-10...

Even easier, just place this text: UseRoaming no on its own line in your ~/.ssh/config file. If you don't have such a file, create it and put this line into it. Doing that will only protect you in that OS X user account, but I bet you only ever use one account on your Mac to SSH anyway.

I updated /private/etc/ssh_config on OS X (system-wide vs. user-specific).

Re: OpenSSH: client bug CVE-2016-0777

#77
post #60

Earlier quoted context omitted.

Actually, I quickly generated a list of undocumented config options: http://sprunge.us/QDSE Edit: Fixed version http://sprunge.us/LVYB

I believe "kerberosauthentication" and "rhostsauthentication" are documented as well. I'd check the "official" OpenBSD man page instead of whatever you have on your system. Regardless, thanks.

In the latest OpenSSH-portable source, those are considered "unsupported" and "deprecated," respectively (which means they're ignored, essentially). See https://gist.github.com/AGWA/e92d4f5343be1f7a941d#file-undoc... as well as the source https://github.com/openssh/openssh-portable/blob/e6c85f8889c...

Re: OpenSSH: client bug CVE-2016-0777

#80
post #47

What was this experimental / undocumented roaming feature even suppose to do?

Complete guess: handle changes of ip address on the client side.

Allow a mobile user to reconnect to a disconnected session without (user) re-authentication.
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