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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fingerprint-auth-ac

SYSTEM-AUTH-AC(5)						File Formats Manual						 SYSTEM-AUTH-AC(5)

NAME

       system-auth-ac,	password-auth-ac,  smartcard-auth-ac, fingerprint-auth-ac, postlogin-ac - Common configuration files for PAMified services
       written by authconfig(8)

SYNOPSIS

       /etc/pam.d/system-auth-ac

DESCRIPTION

       The purpose of this configuration file is to provide common configuration file  for  all  applications  and  service  daemons  calling  PAM
       library.

       The system-auth configuration file is included from all individual service configuration files with the help of the include directive. When
       authconfig(8) writes the system PAM configuration file it replaces the default system-auth file with a symlink pointing	to  system-auth-ac
       and writes the configuration to this file. The symlink is not changed on subsequent configuration changes even if it points elsewhere. This
       allows system administrators to override the configuration written by authconfig.

       The  authconfig	now  writes  the  authentication  modules  also  into  additional  PAM	configuration  files  /etc/pam.d/password-auth-ac,
       /etc/pam.d/smartcard-auth-ac, and /etc/pam.d/fingerprint-auth-ac.  These configuration files contain only modules which perform authentica-
       tion with the respective kinds of authentication tokens.  For example /etc/pam.d/smartcard-auth[-ac] will not contain pam_unix and pam_ldap
       modules and /etc/pam.d/password-auth[-ac] will not contain pam_pkcs11 and pam_fprintd modules.

       The  file  /etc/pam.d/postlogin-ac  contains  common services to be invoked after login. An example can be a module that encrypts an user's
       filesystem or user's keyring and is decrypted by his password.

       The PAM configuration files of services which are accessed by remote connections such as sshd or ftpd now include the  /etc/pam.d/password-
       auth configuration file instead of /etc/pam.d/system-auth.

EXAMPLE

       Configure  system  to  use  pam_tally2  for  configuration  of maximum number of failed logins. Also call pam_access to verify if access is
       allowed.

       Make system-auth symlink point to system-auth-local which contains:

       auth	       requisite       pam_access.so
       auth	       requisite       pam_tally2.so deny=3 lock_time=30 
					     unlock_time=3600
       auth	       include	       system-auth-ac
       account	       required        pam_tally2.so
       account	       include	       system-auth-ac
       password        include	       system-auth-ac
       session	       include	       system-auth-ac

BUGS

       None known.

SEE ALSO

       authconfig(8), authconfig-gtk(8), pam(8), system-auth(5)

Red Hat, Inc.							   2010 March 31						 SYSTEM-AUTH-AC(5)