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Re: openssh: privilege separation no longer supported on Cygwin?




On 29/05/2017 11:48, Houder wrote:
On 2017-05-29 10:39, Marco Atzeri wrote:
On 29/05/2017 07:23, Houder wrote:

[snip]
... because, that is, I think, what I am seeing:

 - the userid of child sshd is still 'cyg_server' ...
 - and I get an elevated shell when I login ...

Not what I expected ...

Gr. Henri


Hi Houder,
please read the last Announcement

https://sourceware.org/ml/cygwin-announce/2017-03/msg00028.html

[snip]
It seems you misunderstood the communication:
- the possibility to NOT use "privilege separation" is deprecated
- "privilege separation" will became mandatory

Hi Marco,

Sorry for the misunderstanding. Yes, to my knowledge, PS, privilege
separation, is now mandatory (using a new mechanism under Linux [1]).

[1] sandboxing?

Because of PS, I expect to see an UNprivileged sshd process talking
to the user process (where the ssh command has been executed).

But above all, I expect an UNelevated shell when I login in ...

However, what I get after login (after providing my credentials) is
an ELEVATED shell (yes, Administrators is part of the group set).

Is your user a member of Administrators ?


Now I wonder if this happens because I do NOT observe PS.

Look below, please ... After executing the ssh command, ssh asks for
my credentials ... in stead of providing my credentials, I execute
the ps command in a second terminal. To my surprise, the grandchild
of the listener is executed using "cyg_server" and not "sshd" ...

Currently, I am looking at:

    https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-setuid-overview

Regards,
Henri


on my system as reported by lusrmgr.msc
cyg_server is a privileged user member of Administrators
sshd is a normal user as expected reading ssh-host-config.

The cyg_server account can setuid to other users
otherwise you can not change user id:

$ pstree -u
?─┬─cygrunsrv(cyg_server)───sshd───sshd───bash(marco)───pstree
  ├─mintty(marco)───bash───ssh
  └─mintty(marco)───bash

Regards
Marco






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