Multiple critical vulnerabilities in snom IP phones

SEC Consult Vulnerability Lab Security Advisory < 20150113-0 >


title: Multiple critical vulnerabilities

product: snom IP phones

vulnerable version: all firmware versions <, all firmware branches

of all snom desktop IP phones (3xx, 7xx, 8xx, etc)

are affected

fixed version: (for all desktop phones)

impact: critical


found: 2014-10-24

by: Johannes Greil, Stefan Viehböck

SEC Consult Vulnerability Lab


Vendor description:


"snom technology AG develops and manufacturers Voice-over-IP (VoIP) telephones

based on open standard for enterprise communications.


The devices are suitable for use in all business environments ranging from

home offices to small- and medium-sized enterprises and large corporations.

snom also works directly with carriers, Internet Service Providers, and OEM

customers. The company is globally present through branch offices and a

partner network."



"snom phones (hardware and software) are developed in Germany and strictly

adhere to all applicable security standards (TLS and SRTP). In contrast to

many of our competitors, snom as a German manufacturer is required to abide by

the strict German data protection regulations and laws. This is of

considerable importance for the prevention of phone-tapping."



Business recommendation:


A short security crash test resulted in multiple critical security

vulnerabilities within all desktop IP phones of snom and all firmware


There exist highly critical attack vectors as the IP phones can be completely

compromised (root) by an external attacker. It is possible to e.g.

* add a backdoor to the system which will even survive a factory reset!

* remotely activate the built-in microphone in order to surveil the room where

the phone is located,

* tap into phone calls made or received by the compromised phone (e.g. by

installing a sniffer on the phone),

* redirect phone numbers to premium rate numbers which may result in high


* use the phone as a jump-host into the internal network and attack other


It is highly recommended by SEC Consult not to use this product until a

thorough security review of the firmware has been performed by security

professionals and all identified issues have been resolved.


Vulnerability overview/description:


1) Multiple cross site scripting vulnerabilities


The device's web interface suffers from multiple reflected & stored cross site

scripting vulnerabilities, which may allow an attacker to gain unauthorized

access to the admin interface and further compromise the phone.


2) Path traversal filter bypass


The firmware has a rudimentary filter against path traversal attacks within

URL parameters. E.g. "../" characters within a parameter value will be

filtered. This can be easily bypassed and potentially exploited for further

attacks on the system (e.g. XML minibrowser or action URL features).


3) Directory traversal & privilege escalation


It is possible to directly access the file system via path/directory traversal

attacks within the URL. In order to exploit it, a certain file extension has

to be added and cut off via a null byte which must not be transmitted in URL

encoded form.

Attackers are then able to easily gain access to sensitive files such as the

snom phone configuration file which includes all passwords in cleartext, even

for the admin user account (admin mode) which should not be accessible to a

low privileged user.


4) Command execution via VPN profiles


The phone's firmware supports OpenVPN profiles and the configuration can be

uploaded via a tarball from a remote webserver. Admin access in the web GUI is

needed which can be gained by exploiting other vulnerabilities, such as 3) and


By combining more identified vulnerabilities, even a remote attacker would be

able to compromise the internal phone, e.g. add a XSS payload via CSRF in

order to gain access to the admin mode password, then install the malicious

OpenVPN profile.

The attacker can prepare a malicious OpenVPN configuration file with shell

commands in order to execute arbitrary commands on the IP phone with highest

access rights on the operating system (root).

There exist highly critical attack vectors after gaining root access to the


* add a backdoor to the system which will even survive a factory reset!

* remotely activate the built-in microphone in order to surveil the room where

the phone is located,

* tap into phone calls made or received by the compromised phone,

* use the phone as a jump-host into the internal network and attack other


* etc.

This can also be exploited via TR069 or auto provisioning by a man-in-the-middle

attacker! This can be achieved via the attacks described in 8).


5) Authentication bypass & privilege escalation


Unprivileged users (non-admin accounts) have the ability to change the

settings for functions keys or action URLs on the phone. Attackers are able to

exploit those features in order to gain administrative access rights on the

web GUI and then exploit further vulnerabilities again, e.g. 4).

The webserver does not check for any user credentials when accessed via

localhost. By reconfiguring a function key or action URL to submit a request

to localhost, it is possible to alter any configuration setting, e.g.

overwrite the current admin-mode password and therefore gain admin access


This vulnerability is also automatically exploitable via CSRF, local access to

the phone (e.g. for pressing a function key) is _not_ required!

Further short tests have shown, that an attacker could also use the request

for altering the settings by directly accessing the IP address over the

network. The bypass via localhost was not necessary. This can be achieved by

sending the same malicious request multiple times.


6) Cross-site request forgery issues


Attackers are able to remotely change settings, e.g. the admin mode password,

on the device via CSRF attacks. Furthermore, it is possible to initiate

arbitrary phone calls, e.g. to premium rate numbers, via CSRF!

Short tests have shown that the anti-CSRF feature "use_hidden_tags" was not

effective in the tested firmware version.


7) Remote firmware update by unprivileged users


Unprivileged users are able to perform a firmware update via the web GUI.

This is also exploitable for a remote attacker using CSRF! A local attacker

could otherwise just simply boot the phone.

An attacker would potentially be able to downgrade to a certain older

firmware, in order to make older security bugs for exploitation available

again. The phone presents the unprivileged user an error message, that admin

access is required. But the phone will automatically perform the firmware

update anyways!


8) Plaintext provisioning through snom servers & weak device identifier


Every IP phone contacts the provisioning server of snom at

"" (IP: for an initial setup phase or

after a factory reset in order to retrieve the auto-provisioning URL for the

TR069 server of the ISP. This connection is not secured and uses plaintext

HTTP communication.

Man-in-the-middle attackers (e.g. TAO/QUANTUM attacks, DNS or BGP hijacking,

etc.) can manipulate those requests, use their own TR069 server and install a

backdoor on the phone (e.g. see 4) and afterwards provide the real TR069 URL

for the ISP. The backdoor will survive the new settings/resets or firmware

updates and be available to the attacker.


Furthermore, the phone identifies itself only via the last three bytes of the

MAC address, which can easily be brute-forced. An attacker would be able to

retrieve all TR069 URLs of the ISPs and he could then potentially further

attack those systems.


Proof of concept:


Detailed proof of concept information has been removed from this advisory.

This section will hence only give an overview regarding the vulnerabilities.

1) Multiple cross site scripting vulnerabilities


The following payload can be used within the [removed] parameter in order

to permanently store JavaScript within [removed]. This is also possible by

importing [removed] contents via CSV files:

[payload removed]

The following URL automatically adds a new entry to the phonebook which

contains JS code. This is also exploitable via CSRF to automatically insert

malicious code without user interaction:

[URL removed]


The following URL is also exploitable because the webserver does not

filter error messages. Browsers that do not url-encode the input are affected

(e.g. older IE versions such as v6):

[URL removed]


2) Path traversal filter bypass


In order to bypass the "../" filter, the following can be used as an example:

[payload removed]

The string [removed] at the end is necessary, otherwise the basename will be

duplicated by the system.


3) Directory traversal & privilege escalation


The following URL can be used to gain access to the file /etc/passwd by

combining a real null byte (not URL encoded %00), e.g. by using burp proxy hex

mode, with certain appended file extensions:

[URL removed]

The following URL allows an attacker access to SIP credentials, admin mode

password and other configuration settings in plaintext of the snom config.xml


[URL removed]


4) Command execution via VPN profiles


The following OpenVPN profile can be used in order to open a reverse shell to

the attacker's system. The attacker will gain the highest access rights on the

phone (root):

    dev tun
    proto tcp
    script-security 2
    remote $someArbitraryOpenVPNIP 443
    cipher AES-128-CBC
    auth SHA1
    tls-verify [payload removed]
    resolv-retry infinite
    verb 3

In order to exploit it, any publicly available OpenVPN server can be misused

with any credentials, as the payload is already executed during the initial

TLS setup phase.

It is easily possible to install a backdoor on the phone because the flash

storage is writable. SEC Consult tested this by altering the init script

"[removed]" and added a SSH daemon (as an example, any command can be

run) which will be started on each boot. The init script does not get

overwritten even after a factory reset, hence the backdoor can still be

accessed afterwards.


Attackers with root access can now completely compromise the phone, e.g. alter

the configuration in order to enable call redirection to premium rate numbers,

access the microphone, install a sniffer in order to record incoming/outgoing

phone calls, or attack other internal systems, etc.


5) Authentication bypass & privilege escalation


By using the following URL to localhost as a so-called "action URL" associated

to a function key on the device, it is possible to gain administrative access

rights because the admin-mode password will be set to an attacker-controlled


[URL removed]

This also works when "restrict_uri_queries" and "use_hidden_tags" are set to

"on", sometimes the function key has to be pressed multiple times then.

See vulnerability 6) for infos on how to "press" the function key remotely via


By requesting the following URL with the direct IP address (not localhost)

repeatedly, it was also possible to gain access to admin mode:

[URL removed]


6) Cross-site request forgery issues


The following URL can be used for CSRF attacks in order to initiate phone

calls to arbitrary numbers (e.g. premium rate):

[URL removed]


The following URL will change the function key setting in order to change the

admin mode password (see 5) via CSRF:

a) URL for setting the function key value:

[URL removed]

b) URL for saving the function key modifications:

[URL removed]

c) URL for automatically executing the command of the function key "P1":

[URL removed]


By exploiting other issues in combination with CSRF, such as XSS and the

OpenVPN command execution flaw, it is possible to remotely compromise the

phone via CSRF.


7) Remote firmware update by unprivileged users


The following URL can be used in order to load another firmware onto the

device. The device will immediately switch to the firmware download mode even

when accessed as unprivileged user, although the phone prints an error message

that admin-mode access is required:

[URL removed]


8) Plaintext provisioning through snom servers & weak device identifier


No proof of concept necessary, wireshark shows plaintext communication.


Vulnerable / tested versions:


The IP phone snom 710 has been tested during a short security evaluation crash

test with firmware version pre-installed.

Snom confirmed that _all_ older firmware versions are affected by the documented

security vulnerabilities except the current new release!

Although snom IP phone 710 has been tested, also _all_ other snom desktop IP phone

products (e.g. 3xx, 7xx, 8xx, etc) are affected!


Vendor contact timeline:


2014-10-31: Contacting vendor through, requesting security

contact, attaching responsible disclosure policy & encryption keys

2014-11-04: No answer, contacting, &, attaching responsible disclosure policy &

encryption keys

2014-11-06: Calling German office, trying to reach a security contact, no

useful information received

Contacting other direct contacts of snom via Sales

2014-11-07: Receiving contact for security communication via Sales, exchanging

encryption keys and sending encrypted security advisory to given


2014-11-18: Requesting status update - vulnerabilities have been forwarded to

developers and are being processed

2014-11-28: Telco with new technical snom contact

2014-12-08 - 2014-12-11: Answering questions of snom regarding some

vulnerabilities, postponing advisory release deadline to 13th

January 2015, more time needed

2014-12-30: Requesting status update

2015-01-05: Last fixes are already in progress, scheduled for 13th January,

receiving document containing detailed information regarding the


2015-01-07: Asking which firmware versions and products are affected

2015-01-08: Calling snom, verifying affected products

2015-01-08: Sending adjusted advisory to snom

2015-01-08: Informing and CERT-Bund Germany (BSI) about pending release

2015-01-13: Coordinated release of security advisory




The vendor provides a new firmware version v8.7.5.15 and urges all users to

_immediately_ upgrade to this version!

Vendor security note & firmware download:

Older firmware branches will not be patched and the upgrade to this new

version is therefore absolutely necessary for all users!


According to the vendor, the OpenVPN binary will be removed from the firmware

per default and can be loaded as a small firmware update afterwards if

necessary (see vendor security note above). Users of the OpenVPN feature will

get a warning as they will be affected by the identified vulnerability again

after enabling the feature.




No workaround available. The vendor urges all customers to immediately upgrade

the firmware of all snom IP phones.


Advisory URL:




SEC Consult Vulnerability Lab

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Phone: +43 1 8903043 0

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EOF J. Greil / @2015