The below 3 issues have been tested and verified working on the following
Canon Printer models (May affect more, but this is all I was able to test
against):
MG3100, MG5300, MG6100, MP495, MX340, MX870, MX890, MX920

#1 (CVE-2013-4613): Canon printers do not require a password for the
administrative interfaces by default. Unauthorized users on the network may
configure the printer. If the printer is exposed to the public internet,
anonymous users may make configuration changes as well. This should be
corrected by requiring a password, even if only a default, but should
recommend users to change it upon initial setup of the device.

#2 (CVE-2013-4614): The administrative interface on these printers allow a
user to enter a WEP/WPA/WPA2 pre-shared key. Once a key is entered, when a
user browses the configuration page again, they can view the current
password in clear-text. Once a password is configured, it should not allow
the user to read it again. If the user wants to change the password, they
should be required to enter a new one, which then overwrites the old one.

#3 (CVE-2013-4615): There is a denial of service condition in the
administrative interface on the devices. Using specially crafted HTTP
requests, it is possible to cause the device to no longer respond. This
requires the device to be turned off, and then back on again, to which the
printer will display a message about not being properly turned off, on the
display (if model has a display).

I have disclosed all 3 of these issues to Canon, and unfortunately they do
not feel it is necessary to fix them (In all fairness, they're not super
high severity). More details, along with PoC and Metasploit modules are
available here: *
http://www.mattandreko.com/2013/06/canon-y-u-no-security.html*

Timeline:
May 27, 2013: Initial Email to vendor's support
May 28, 2013: Vendor support emailed for additional details
May 28, 2013: Sent a proof-of-concept exploit for the DoS vulnerability to
vendor
May 30, 2013: Vendor escalated issue internally
June 4, 2013: Vendor notification that issue has been escalated to
manufacturer
June 14, 2013: Vendor notification that they will not fix issues
June 18, 2013: Public Disclosure