SEC Consult Vulnerability Lab Security Advisory < 20231205-0 >
=======================================================================
               title: Argument injection leading to unauthenticated RCE and
                      authentication bypass
             product: Atos Unify OpenScape Session Border Controller (SBC)
                      Atos Unify OpenScape Branch
                      Atos Unify OpenScape BCF
  vulnerable version: OpenScape SBC before V10 R3.4.0
                      OpenScape Branch before V10 R3.4.0
                      OpenScape BCF V10 before V10 R10.12.00 and V10 R11.05.02
       fixed version: OpenScape SBC V10 R3.4.0 or higher
                      OpenScape Branch V10 R3.4.0 or higher
                      OpenScape BCF V10 R10.12.00 or higher, V10 R11.05.02
          CVE number: CVE-2023-6269
              impact: Critical
            homepage: https://unify.com/
               found: 2023-09-01
                  by: Armin Weihbold (Office Linz)
                      SEC Consult Vulnerability Lab

                      An integrated part of SEC Consult, an Eviden business
                      Europe | Asia

                      https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------
"Unify is is the Atos brand for communication and collaboration solutions
Unify is the newest member of the Atos family, combining Atos’ knowledge and
reputation in the IT services market with Unify’s expertise in unified
communications and collaboration to provide customers with seamless services
solutions for their entire digital portfolio. Within Atos, Unify continues to
deliver a unique integrated proposition for unified communications and real
time capabilities."

Source: https://unify.com/en/expert/unify


Business recommendation:
------------------------
SEC Consult recommends users of this solution to immediately install the latest
patch from the vendor.

Furthermore, an in-depth security analysis performed by security professionals
is highly advised, as the software may be affected from other security issues.


Vulnerability overview/description:
-----------------------------------
1) Argument injection leading to unauthenticated RCE and authentication bypass (CVE-2023-6269)
The administrative web interface insufficiently escapes supplied login
credentials before passing them to a user management application, leading to
an unauthenticated attacker being able to gain root access to the appliance
via SSH.

Another possibility to exploit this vulnerability is to append a special
argument during logon to completely bypass the authentication of the web interface.
A previously unauthenticated attacker can logon as administrator without any
known credentials.


Proof of concept:
-----------------
1) Argument injection leading to unauthenticated RCE and authentication bypass (CVE-2023-6269)
Example 1) Gaining unauthenticated SSH root access

The file receiving data from the login page is `auth.php`, here the
user-provided credentials are passed on to the function
`PasswordMgr::authPassword` after some checks on the supplied username.

```php
// /srv/www/htdocs/auth.php
// [...]
     $ret=false;
     $real_user='';
     $error = '';
     $local_user=strip_tags($_POST['username']);
// [...]
     if( !sessionLimitReached() )
     {
         // Authenticate user/password...
         $privilege = PasswordMgr::getUserPrivilege($local_user);
         if (($local_user == 'assistant') || ($local_user == 'cdr') || (!PasswordMgr::isUserEnabled($local_user))){
             $ret = false;
         }
         else {
             switch ($privilege) {
                 case 'admin':
                     $ret = PasswordMgr::authPassword($_POST["username"], $_POST["password"], $error, $real_user, $local_user, FALSE);
                     break;
                 // [...]
             }
         }
         // [...]
     }
// [...]

```

The function `PasswordMgr::authPassword` in `core/PasswordMgr.php` is just a
wrapper around `call_osbpasswd` in the same file.


```php
// /srv/www/htdocs/core/PasswordMgr.php

public static function authPassword($username, $password, &$error, &$real_user, &$local_user, $local = FALSE)
{
     $error='';
     if ( PasswordMgr::call_osbpasswd("auth", $username, $password, $error, $real_user, $local_user, $local ) )
     {
         $error='Current Password does not match user';
         return false;
     }
     return true;
}
```

The function `call_osbpasswd` is responsible for anything related to user
management, it does this by constructing shell arguments and supplying them to
the executable `/osb/bin/osbpasswd` which is executed with root privileges via
`cfgUtilExecSudo`. This executable handles the actual authentication, creation
of users, and other tasks.
In the case of authentication the arguments are written to a temporary file
and read from there.
Before that the supplied password is escaped using `escapeshellcmd` instead of
`escapeshellarg`. This means that space characters (hex 0x20) in the password
are left intact allowing for argument injection.

```php
// /srv/www/htdocs/core/PasswordMgr.php

public static function call_osbpasswd( $method, $username, $password, &$output, &$real_user, &$local_user, $local, $extraArg = '' )
{
     // [...]
     $curruser = 'GUI';
     // [...]

     $params = "$method";
     if ($local)          $params .= ' --local';
     if ($username != '') $params .= " --user $username";
     if ($curruser != '') $params .= " --curruser $curruser";
     if ($extraArg != '') $params .= "$extraArg";

     $file = '';
     // [...]
     else {
         $params .= " --password ";
         $fakePar = $params."xxxxxx";
         $params .= escapeshellcmd($password);
         $params .= "\n";
         $file = tempnam('/osb/var/tmp','osbpasswd.'.md5($params).'.');
         /*E.g.: /opt/openbranch/var/tmp/osbpasswd.f9e2a9fcf29c6275830257316d560e27.CG4IcQ */
         cfgUtilEcho( $params, $file );
         $command = "/osb/bin/osbpasswd ".$fakePar." --file ".$file;
     }

     $outArray = array();
     $ret = cfgUtilExecSudo($command, $outArray, FALSE, TRUE);
     // [...]
     return $ret;
}
```

The function that is responsible for parsing command line arguments
in the called application `/osb/bin/osbpasswd` iterates over arguments and
sets global variables based on them. This is done in a loop and no check is
done if that argument was already set. This means an attacker can override all
parameters by specifying them again.

```C
int parse_arguments(int argc, char **argv, int n)
{
   // [...]
   while ( n < argc && argv[n] ) {
     // [...]
     else if ( !strcmp("--user", argv[n]) ) {
         if ( ++n < argc )
            arg_user = argv[n];
     }
     else if ( !strcmp("--shell", argv[n]) ) {
         if ( ++n < argc )
             arg_shell = argv[n];
     }
     // [...]
     else if ( !strcmp("auth", argv[n]) ) {
         arg_command_name = argv[n];
         arg_command_number = 1;
     }
     else if ( !strcmp("add", argv[n]) ) {
         arg_command_name = argv[n];
         arg_command_number = 6;
     }
     // [...]
     ++n;
   }
   return 0LL;
}
```

The combination of faulty escaping of the supplied password and overly
permissive parsing of arguments in the called binary leads to an attacker being
able to request arbitrary operations from the `/osb/bin/osbpasswd` binary with
arbitrary arguments. An attacker could for example create a new user with SSH
access and change the password of the root user leading to a complete
compromise of the system.

To demonstrate the vulnerability, it is sufficient to [...]

[ Proof of concept removed ]

- this creates a new user with SSH access, the second one [...]

[ Proof of concept removed ]

which changes the password of the root user. The attacker can then login [...]
to gain root access.



Example 2) Bypassing the web interface logon as administrator
As described in example 1, the same vulnerability can also be exploited to
bypass the logon for the web interface and immediately gain access as
administrator because the arguments for the command-line tool are passed and
evaluated.

By supplying the [...] following [...] string [...], it is possible to logon
without known credentials:

[ Proof of concept removed ]

[...]
Afterwards the attacker is logged on as administrator (or any other supplied
user account).


Vulnerable / tested versions:
-----------------------------
The following version has been tested which was the latest version available
at the time of the test:

* Atos Unify OpenScape Session Border Controler (SBC) Firmware Version V10 R3.3.0

According to vendor, versions before V10 R3.3.0 are affected as well.

The vendor confirmed that the following products are vulnerable:
* Atos Unify OpenScape SBC V10 before V10 R3.4.0
* Atos Unify OpenScape Branch V10 before V10 R3.4.0
* Atos Unify OpenScape BCF V10 before V10R10.12.00 and V10R11.05.02


Vendor contact timeline:
------------------------
2023-09-13: Contacting vendor through email obso@atos.net; sending
             encrypted advisory (S/MIME)
2023-09-25: Call with vendor, patch has already been developed, available
             internally for testing & QA since 22nd.
2023-09-26: Preliminary vendor security advisory available, giving feedback
             regarding recommendations. Vendor informs customers in advance
             (TLP:AMBER), patch planned for 2023-09-27.
2023-10-04: Vendor security advisory public release (TLP:WHITE).
2023-10-06: Asking regarding next steps for affected product Atos Unify
             OpenScape BCF.
2023-10-10: Vendor confirms that OpenScape BCF is affected as well and added
             it to their advisory.
2023-11-27: Reserving CVE-2023-6269 and sending it to vendor, defining
             release date of 5th December.
2023-12-05: Coordinated release of security advisory.


Solution:
---------
The vendor provides a patch for the affected products:
* Atos Unify OpenScape Session Border Controller Firmware Version V10 >=R3.4.0
* Atos Unify OpenScape Branch version V10 >=R3.4.0
* Atos Unify OpenScape BCF version V10 >=V10R10.12.00 and V10R11.05.02

The patches can be obtained for registered customers through the vendor's
download server:
https://sws.unify.com/SWSIntranet/SWSIntra.aspx or via
https://unify.com/en/partner/partnerportal
https://unify.com/en/support/kunden-support-portal

Furthermore, the vendor has also released a security advisory which is
available here:
https://networks.unify.com/security/advisories/OBSO-2310-01.pdf


Workaround:
-----------
In addition to deploying the patch, limit access to the administrative
web application and SSH ports to authorized personnel on the network level.


Advisory URL:
-------------
https://sec-consult.com/vulnerability-lab/


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab
An integrated part of SEC Consult, an Eviden business
Europe | Asia

About SEC Consult Vulnerability Lab
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Eviden business. It ensures the continued knowledge gain of SEC Consult in the
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SEC Consult Vulnerability Lab supports high-quality penetration testing and
the evaluation of new offensive and defensive technologies for our customers.
Hence our customers obtain the most current information about vulnerabilities
and valid recommendation about the risk profile of new technologies.

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EOF A. Weihbold / @2023