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Zoom X4/X5 ADSL Modem and Router -Unauthenticated Remote Root Command Execution

Vulnerable Products -

Zoom X4 ADSL Modem and Router running Nucleus/4.3
UPnP/1.0Virata-EmWeb/R6_2_0 Server All GS Firmware versions
Zoom X5 ADSL Modem and Router running Nucleus/4.3
UPnP/1.0Virata-EmWeb/R6_2_0 Server All GS Firmware versions

Note: A similar vulnerability was reported several years ago on the
Zoom X3 ADSL Modem using a SOAP API call. Many of these
vulnerabilities affect X3 in the same manner, without needing to use a


When UPnP services and WAN http administrative access are enabled,
authorization and credential challenges can be bypassed by directly
accessing root privileged abilities via a web browser URL.

All aspects of the modem/router can be changed, altered and controlled
by an attacker, including gaining access to and changing the PPPoe/PPP
ISP credentials.


Timeline with Vendor-
Have had no response from Zoom Telephonics since first reporting the
problem on June 28. Subsequent emails have been sent with no response.

Root Cause Observed-
-As in most IGD UPnP routers and modems, where root vulnerabilities
are prevalent, these modems contain the same privileged tunnel between
either side of the router to be traversed without authentication.  The
code and layout of the device plays a large role as well.

Code/Script Vulnerabilities-

-Form tags and actions ids usually hidden are easily seen from the
html source, no sanitization of client side input is occurring and
root overrides such as 'Zadv=1' can be invoked by any user.

-No cookie authentication is done once several of the first bypass is
executed, allowing for "Cookie: sessionId=invalid" to pass admin commands.

-The SQL injection UNION SELECT 1,2,3,4,5,6,7-- added to the end of
any URL page calling a table value, such as /MainPage?id=25, will
bring up the system status page, with each interface visible and

Patches or Fixes-
At this time, there are no known patches or fixes.

Vulnerability proofs and examples-
All administrative items can be accessed through these two URLs

--Menu Banner

-Advanced Options Menu

Example commands that can be executed remotely through a web browser
URL, or a modified HTTP GET/POST requests-

-Change Password for admin Account

On Firmware 2.5 or lower

On Firmware 3.0-

-Clear Logs

-Remote Reboot to Default Factory Settings-
Warning - For all intents and purposes, this action will almost always
result in a long term Denial of Service attack.

-Create New Admin or Intermediate Account-
On Firmware 2.5 or lower

On Firmware 3.0-

Mitigation and Workarounds-
Adv.Options --> UPnP --> --> Disable UPnP --> Write Settings to Flash --> Reboot
Adv.Options --> Firewall Configuration --> Enable 'Attack Protection'
'DOS Proctection''Black List'--> Write Settings to Flash
Adv.Options --> Management Control --> Disable WAN Management from all
fields -->  Write Settings to Flash
Always change the default Username and Password, though this will
nothelp mitigate this vulnerability