Following issue "Compilation error when disabling pubkey authentication (DROPBEAR_SVR_PUBKEY_AUTH)" from davidbernard04, code is modified to take in account that requesting information from method "ses.authstate.pubkey_info" isn't possible since the method is disabled when DROPBEAR_SVR_PUBKEY_OPTIONS_BUILT value is 0.
When dropbear is used in a very restricted environment (such as in a
initrd), the default user shell is often also very restricted
and doesn't take care of setting the PATH so the user ends up
with the PATH set by dropbear. Unfortunately, dropbear always
sets "/usr/bin:/bin" as default PATH even for the root user
which should have /usr/sbin and /sbin too.
For a concrete instance of this problem, see the "Remote Unlocking"
section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/
It speaks of a bug in the initramfs script because it's written "blkid"
instead of "/sbin/blkid"... this is just because the scripts from the
initramfs do not expect to have a PATH without the sbin directories and
because dropbear is not setting the PATH appropriately for the root user.
I'm thus suggesting to use the attached patch to fix this misbehaviour (I
did not test it, but it's easy enough). It might seem anecdotic but
multiple Kali users have been bitten by this.
From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403
Why:
Running dropbear as a user (rootless) is aided if
files and programs can be saved/removed without
needing sudo.
What:
Use the same convention as DROPBEAR_DEFAULT_CLI_AUTHKEY;
if not starting with '/', then is relative to hedge's /home/hedge:
*_PRIV_FILENAME
DROPBEAR_PIDFILE
SFTPSERVER_PATH
default_options.h commentary added.
Changes kept to a minimum, so log entry in svr_kex.c#163
is refactored.
From:
Generated hostkey is <path> ... <finger-print>
to:
Generated hostkey path is <path>
Generated hostkey fingerprint is <fp>
Otherwise the unexpanded path was reported.
Patch modified by Matt Johnston
Signed-off-by: Begley Brothers Inc <begleybrothers@gmail.com>
This allows ASLR to re-randomize the address
space for every connection, preventing some
vulnerabilities from being exploitable by
repeated probing.
Overhead (memory and time) is yet to be confirmed.
At present this is only enabled on Linux. Other BSD platforms
with fexecve() would probably also work though have not been tested.
Lower class levels are less well defined, and non-interactive
SSH can carry various different types of applications.
This change also sets lowdelay class (AF21) earlier in an an outbound
dbclient session
This handles the case where a svrchansess has separate FDs
for nopty, but a single FD for pty mode.
The use of sepfds was also previously incorrect for X11 and
agent forwarding
For the sake of review, this commit alters only the code; the affiliated
comments within the source files also need to be updated, but doing so
now would obscure the operational changes that have been made here.
* All on/off options have been switched to the numeric `#if' variant;
that is the only way to make this `default_options.h.in' thing work
in a reasonable manner.
* There is now some very minor compile-time checking of the user's
choice of options.
* NO_FAST_EXPTMOD doesn't seem to be used, so it has been removed.
* ENABLE_USER_ALGO_LIST was supposed to be renamed DROPBEAR_USER_ALGO_LIST,
and this commit completes that work.
* DROPBEAR_FUZZ seems to be a relatively new, as-yet undocumented option,
which was added by the following commit:
commit 6e0b539e9c
Author: Matt Johnston <matt@ucc.asn.au>
Date: Tue May 23 22:29:21 2017 +0800
split out checkpubkey_line() separately
It has now been added to `sysoptions.h' and defined as `0' by default.
* The configuration option `DROPBEAR_PASSWORD_ENV' is no longer listed in
`default_options.h.in'; it is no longer meant to be set by the user, and
is instead left to be defined in `sysoptions.h' (where it was already being
defined) as merely the name of the environment variable in question:
DROPBEAR_PASSWORD
To enable or disable use of that environment variable, the user must now
toggle `DROPBEAR_USE_DROPBEAR_PASSWORD'.
* The sFTP support is now toggled by setting `DROPBEAR_SFTPSERVER', and the
path of the sFTP server program is set independently through the usual
SFTPSERVER_PATH.
This change adds a -c option to dropbear, to force the session to use a
specific command, in a similar fashion to OpenSSH's ForceCommand
configuration option.
This is useful to provide a simple fixed service over ssh, without
requiring an authorized key file for the per-key forced_command option.
This setting takes precedence over the channel session's provided
command, and the per-key forced_command setting.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
(possibly via authorized_keys(5) restrictions), even when a
pseudo-terminal has been allocated for the session. In other words,
only display the MOTD when the server starts the user's default shell.
if (connecting || ptys || x11) tos = LOWDELAY;
else if (tcp_forwards) tos = 0;
else tos = BULK;
TCP forwards could be either lowdelay or bulk, hence the default priority.
