SOCKS proxy & PAM configuration exposure Post: 302986627

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Top Forums UNIX for Advanced & Expert Users SOCKS proxy & PAM configuration exposure Post 302986627 by rbatte1 on Monday 28th of November 2016 12:02:49 PM

11-28-2016

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SOCKS proxy & PAM configuration exposure

I've got a problem with a proxy configuration. We have an LDAP group that lists all users who are authorised to use the proxy to FTP (usually Filezilla) out to the world, and by implication those not in the group should be denied. My users are delighted that this has been enabled and those that wish to get out can do so, however we're not stopping anyone not in the group (and therefore not authorised)

We found this out because I'm not authorised but whilst troubleshooting for a user I connected out no problem. That ended up being a user password problem, so they failed the LDAP check and so PAM prevented the connection.

I haven't got a test server so I will have to get a slot outside business hours (which will be a nightmare in itself) to try out my thoughts but I wanted to sanity check it first. The server is running CentOS The proxy server is SOCKS in /usr/sbin/ss5 and running as the root user.

My suspicion is about the PAM file, /etc/pam.d/ss5 and the way it has been set up. We have this:-

Code:

#%PAM-1.0
auth       include      system-auth
account    required     pam_nologin.so
auth       required     pam_wheel.so use_uid group=SocksUsers
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    required     pam_loginuid.so

My theory is that the line defining the allowed group also includes the use_uid option and given that the ss5 daemon is running as the super-user everyone is automatically authenticated. There is a proxy authentication required, but messages is /var/log/secure give me this when I authenticate to the proxy correctly and give invalid credentials to an internet-based FTP site:-

Code:

Nov 28 15:03:14 gateway-b ss5: pam_unix(ss5:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=  user=donald.trump
Nov 28 15:03:14 gateway-b ss5: pam_winbind(ss5:auth): getting password (0x00000008)
Nov 28 15:03:14 gateway-b ss5: pam_winbind(ss5:auth): pam_get_item returned a password
Nov 28 15:03:14 gateway-b ss5: pam_winbind(ss5:auth): user 'donald.trump' granted access

Yes, some Windoze joker created me a test account with that name. Sorry about that. No political persuasion inferred, naturally - I'm British after all.

Before I try to get a slot, does anyone want to contradict my theory? I'd be grateful for avoiding unnecessary effort if I've gone off on the wrong track.

Many thanks, in advance,
Robin

rbatte1

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LEARN ABOUT DEBIAN

pam_ldap

pam_ldap(8)						      System Manager's Manual						       pam_ldap(8)

NAME

       pam_ldap - PAM module for LDAP-based authentication

SYNOPSIS

       pam_ldap.so [...]

DESCRIPTION

       This is a PAM module that uses an LDAP server to verify user access rights and credentials.

OPTIONS

       use_first_pass
	      Specifies that the PAM module should use the first password provided in the authentication stack and not prompt the user for a pass-
	      word.

       try_first_pass
	      Specifies that the PAM module should use the first password provided in the authentication stack and if that fails prompt  the  user
	      for a password.

       nullok Specifying this option allows users to log in with a blank password.  Normally logins without a password are denied.

       ignore_unknown_user
	      Specifies  that  the  PAM module should return PAM_IGNORE for users that are not present in the LDAP directory.  This causes the PAM
	      framework to ignore this module.

       ignore_authinfo_unavail
	      Specifies that the PAM module should return PAM_IGNORE if it cannot contact the LDAP server.  This causes the PAM framework  to  ig-
	      nore this module.

       no_warn
	      Specifies that warning messages should not be propagated to the PAM application.

       use_authtok
	      This  causes the PAM module to use the earlier provided password when changing the password. The module will not prompt the user for
	      a new password (it is analogous to use_first_pass).

       debug  This option causes the PAM module to log debugging information to syslog(3).

       minimum_uid=UID
	      This option causes the PAM module to ignore the user if the user id is lower than the specified value. This can be  used	to  bypass
	      LDAP checks for system users (e.g. by setting it to 1000).

MODULE SERVICES PROVIDED

       All services are provided by this module but currently sessions changes are not implemented in the nslcd daemon.

FILES

       /etc/pam.conf
	      the main PAM configuration file

       /etc/nslcd.conf
	      The configuration file for the nslcd daemon (see nslcd.conf(5))

SEE ALSO

       pam.conf(5), nslcd(8), nslcd.conf(5)

AUTHOR

       This manual was written by Arthur de Jong <arthur@arthurdejong.org>.

Version 0.8.10							     Jun 2012							       pam_ldap(8)