SEC Consult Vulnerability Lab Security Advisory < 20220615-0 > ======================================================================= title: Hardcoded Backdoor User and Outdated Software Components product: Nexans FTTO GigaSwitch industrial/office switches HW version 5 vulnerable version: See "Vulnerable / tested versions" fixed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 Vulnerability overview/description: ----------------------------------- 1) Outdated Vulnerable Software Components A static scan with the IoT Inspector (ONEKEY) revealed outdated software packages that are used in the devices' firmware.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 Proof of concept: ----------------- 1) Outdated Vulnerable Software Components Based on an automated scan with the IoT Inspector (ONEKEY) the following third party software packages were found to be outdated: Firmware version 6.02L: BusyBox 1.20.2 Dropbear SSH 2012.55 GNU glibc 2.17 lighttpd 1.4.48 OpenSSL 1.0.2h The following CVEs were verified with MEDUSA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 support.ans@nexans.com. 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. Workaround: ----------- None Advisory URL: ------------- https://sec-consult.com/vulnerability-lab/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC Consult Vulnerability Lab SEC Consult, an Atos company Europe | Asia | North America About SEC Consult Vulnerability Lab The SEC Consult Vulnerability Lab is an integrated part of SEC Consult, an Atos company. It ensures the continued knowledge gain of SEC Consult in the field of network and application security to stay ahead of the attacker. The 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. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? Send us your application https://sec-consult.com/career/ Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices https://sec-consult.com/contact/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: security-research at sec-consult dot com Web: https://www.sec-consult.com Blog: http://blog.sec-consult.com Twitter: https://twitter.com/sec_consult EOF T. Weber / @2022