Nexans FTTO GigaSwitch Outdated Components / Hardcoded Backdoor Vulnerability

=======================================================================
               title: Hardcoded Backdoor User and Outdated Software Components
             product: Nexans FTTO GigaSwitch industrial/office switches HW version 5
  vulnerable version: See "Vulnerable / tested versions"
       fixed version: V6.02N, V7.02
          CVE number: CVE-2022-32985
              impact: High
            homepage: https://www.nexans.com/
               found: 2020-05-25
                  by: T. Weber (Office Vienna)
                      SEC Consult Vulnerability Lab

                      An integrated part of SEC Consult, an Atos company
                      Europe | Asia | North America

                      https://www.sec-consult.com

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

Vendor description:
-------------------
"As a global player in the cable industry, Nexans is behind the scenes
delivering the innovative services and resilient products that carry thousands
of watts of energy and terabytes of data per second around the world. Millions
of homes, cities, businesses are powered every day by Nexans’ high-quality
sustainable cabling solutions. We help our customers meet the challenges they
face in the fields of energy infrastructure, energy resources, transport,
buildings, telecom and data, providing them with solutions and services for the
most complex cable applications in the most demanding environments."

Source: https://www.nexans.com/company/What-we-do.html


Business recommendation:
------------------------
The vendor provides a patch which should be installed immediately.

SEC Consult recommends to perform a thorough security review of these
products conducted by security professionals to identify and resolve all
security issues.


Vulnerability overview/description:
-----------------------------------
1) Outdated Vulnerable Software Components
A static scan with the IoT Inspector (ONEKEY) revealed outdated software packages that
are used in the devices' firmware. Four of them were verified by using the
MEDUSA scalable firmware runtime.


2) Hardcoded Backdoor User (CVE-2022-32985)
A hardcoded root user was found in "/etc/passwd". In combination with the
invoked dropbear SSH daemon in the libnx_apl.so library, it can be used on port
50201 and 50200 to login on a system shell.


Proof of concept:
-----------------
1) Outdated Vulnerable Software Components
Based on an automated scan with the IoT Inspector (ONEKEY) the following third party
software packages were found to be outdated:

Firmware version 6.02L:
BusyBox       1.20.2
Dropbear SSH  2012.55
GNU glibc     2.17
lighttpd      1.4.48
OpenSSL       1.0.2h

The following CVEs were verified with MEDUSA scalable firmware emulation:

* CVE-2015-9261 (Unzip)
The crafted ZIP archive "x_6170921383890712452.bin" was taken from:
https://www.openwall.com/lists/oss-security/2015/10/25/3
Execution inside the firmware emulation:

bash-4.2# unzip x_6170921383890712452.bin
Archive:  x_6170921383890712452.bin
   inflating: ]3j½r«IK-%Ix
do_page_fault(): sending SIGSEGV to unzip for invalid read access from 735ededc
epc = 0044bb28 in busybox[400000+99000]
ra  = 0044b968 in busybox[400000+99000]
Segmentation fault


* CVE-2015-0235 (gethostbyname "GHOST" buffer overflow)

PoC code was taken from:
https://gist.github.com/dweinstein/66e6a088191ac0e8105c


* CVE-2015-7547 (getaddrinfo buffer overflow)

PoC code was taken from:
https://github.com/fjserna/CVE-2015-7547

-bash-4.4# python /medusa_exploits/cve-2015-7547-poc.py &
[1] 259
-bash-4.4# chroot /medusa_rootfs/ bin/bash
bash-4.2# cd /medusa_exploits/
bash-4.2# ./cve-2015-7547_glibc_getaddrinfo
[UDP] Total Data len recv 36
[UDP] Total Data len recv 36
Connected with 127.0.0.1:34356
[TCP] Total Data len recv 76
[TCP] Request1 len recv 36
[TCP] Request2 len recv 36
Segmentation fault


* CVE-2017-16544 (shell autocompletion vulnerability)

A file with the name "\ectest\n\e]55;test.txt\a" was created to trigger the
vulnerability.
-------------------------------------------------------------------------------
# ls "pressing <TAB>"
test
]55;test.txt
#
-------------------------------------------------------------------------------


2) Hardcoded Backdoor User (CVE-2022-32985)
The hardcoded system user, reachable via the dropbear SSH daemon was found due
to multiple indications on the system. The undocumented root user itself was
contained in the "passwd" file:

Content of the file "/etc/passwd".
-------------------------------------------------------------------------------
root:oFQzvQf5qrI56:0:0:root:/home/root:/bin/sh
[...]
-------------------------------------------------------------------------------

A suspicious port for the SSH daemon was chosen in the config file of dropbear:

Content of the file "/etc/init.d/dropbear":
-------------------------------------------------------------------------------
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/sbin/dropbear
NAME=dropbear
DESC="Dropbear SSH server"
PIDFILE=/var/run/dropbear.pid

DROPBEAR_PORT="50200 -p 50201"
[...]
-------------------------------------------------------------------------------

This is invoked from "/usr/lib/libnx_apl.so.0.0.0", which can be seen in the
following pseudo-code:
-------------------------------------------------------------------------------
void dropbear_server_init(char param_1)

{
   __pid_t __pid;
   char *pcVar1;
   int aiStack16 [2];

   __pid = fork();
   if (__pid == 0) {
     __pid = fork();
     if (__pid != 0) {
                     /* WARNING: Subroutine does not return */
       exit(0);
     }
     if (param_1 == '\0') {
       pcVar1 = "/etc/init.d/dropbear stop";
     }
     else {
       pcVar1 = "/etc/init.d/dropbear start";                               <---
     }
     execl("/bin/sh","sh",&DAT_2cd91564,pcVar1,0);
   }
   else {
     waitpid(__pid,aiStack16,0);
   }
   return;
}
-------------------------------------------------------------------------------


This function is called if a specific command is issued in the CLI interface:
-------------------------------------------------------------------------------
[...]
   iVar6 = telnet_cmp_command((char *)(param_3 + 0xf2),"ssh",2);
   if (iVar6 != 0) {
     if (param_2 < 4) {
       netbuf_fwd_sprintf(param_1,"\r\n%%Error: Parameter missing\r\n");
       iVar6 = shared_mem_get_addr(&var_shm);
       iVar7 = shared_mem_get_addr(&var_shm);
       uVar8 = shared_mem_read_u8(&var_shm,iVar7 + 0x161a);
       shared_mem_write_u8(&var_shm,iVar6 + 0x161a,uVar8 & 0xff | 0x10);
       return;
     }
     iVar6 = telnet_cmp_command((char *)(param_3 + 0x16b),"start",1);
     if (iVar6 != 0) {
       dropbear_server_init('\x01');                                        <---
       netbuf_fwd_sprintf(param_1,"Starting dropbear...\r\n");
       return;
     }
     iVar6 = telnet_cmp_command((char *)(param_3 + 0x16b),"stop",1);
     if (iVar6 != 0) {
       dropbear_server_init('\0');                                          <---
       netbuf_fwd_sprintf(param_1,"Stopping dropbear...\r\n");
       return;
     }
     netbuf_fwd_sprintf(param_1,"Uknown dropbear command...\r\n");
     return;
[...]
-------------------------------------------------------------------------------
The mentioned library is used in the CLI program that is running on the device.


Vulnerable / tested versions:
-----------------------------
The following firmware versions have been tested:

* Nexans FTTO GigaSwitch HW Version 5 (all industrial/office switches) / Firmware 6.02L
* Nexans FTTO GigaSwitch HW Version 5 (all industrial/office switches) / Firmware 5.04M


Vendor contact timeline:
------------------------
2020-05-28: Contacting the vendor's PSIRT under the following link:
             http://www.nexans-ans.de/support/index.php?u=security_portal_sendmail
      No answer.
2020-06-08: Contacting vendor again via [email protected] Extended
             deadline by 11 days.
2020-06-16: Telephone call with Nexans representative. Security advisory was
             received. It will be reviewed to confirm the found issues.
2020-06-26: Telephone call with Nexans representative. Nexans is working on the
             reported issues and will remove the dropbear daemon as first
             measure.
2020-08-04: Vendor stated that a fix for the outdated software components will
             be available in November.
2020-11-12: Asked for status update.
2020-11-16: Contact stated, that firmware test will need more time. Updates are
             estimated to be ready in Q1 of 2020.
2020-11-20: Vendor confirmed Q1 as estimated disclosure date.
2021-01-21: Asked for status update; Vendor stated that the release with all
             fixes is aimed to be published end of Q1.
2021-03-09: Asked for status update.
2021-03-17: Vendor stated that the firmware is in testing stage. The fixed
             firmware will be released in May.
2021-06-10: Asked for status update.
2021-06-14: Vendor stated that the firmware is not ready due to COVID19 and
             homeschooling. The fixed firmware will be released end of August.
2021-08-31: Asked for status update.
2021-09-07: Vendor stated that the fixed firmware will be ready end of 2021.
2022-05-23: Informed vendor that the advisory will be released mid of June 2022.
2022-05-24: Firmware V7.02 is available for download which fixes most outdated
             components issues.
2022-06-15: Release of security advisory.


Solution:
---------
The vendor provides an updated firmware here:
https://www.nexans-ans.de/support/firmware/

Firmware version V6.02N has the backdoor removed and was already published a while ago.
Version V7.02 also has the backdoor removed and most of the outdated software issues.