Check_MK Werk 0766: Changed transid implemtation to work as CSRF protection (Fixes CVE-2014-2330)

Lars Michelsen lm at mathias-kettner.de
Fri Aug 1 11:00:42 CEST 2014


ID:          0766
Title:       Changed transid implemtation to work as CSRF protection (Fixes CVE-2014-2330)
Component:   Multisite
Level:       3
Class:       Security Fix
Version:     1.2.5i2

This change fixes possible attacks against Check_MK Multisite users. In previous
versions a possible attacker could try to make the browsers of authenticated users
open URLs of the Check_MK Multisite GUI to execute actions e.g. within WATO without
knowledge of the attacked user.

To make such an attack possible, there are several things needed: The user must be
authenticated with multisite and have enough permission within multisite to execute
the actions the attacker wants to use, the attacker needs to know the exact URL to the
Multisite GUI. Then the attacker needs to make the user either click on a manipulated
link or open a manipulated webpage which makes the browser of the user, where the user
is authenticated with multisite, open the URL the attacker wants to make it open.

The multisite GUI makes use of transids (transaction ids) when processing form
submissions or actions. The transids were mainly used to prevent double execution
of actions when reloading the page which performed the action in the browser.
Now we changed internal handling of the transid to make it also prevent CSRF attacks.
The transid is now some kind of shared secret between the webserver and the browser
of the user. This ensures a form submission is intended by a previously requested page.

This change impicates an incompatible change: In case you use a script which opens
multisite pages to perform an action, e.g. set a downtime and use this with a regular
user account which authenticates by username/password, the script won't work anymore
after this change.
The way to go is to adapt the script and change the user to authenticate with an
automation secret instead of a password. For this kind of authentication, you will
need to user other URL parameters (_username=... and _secret=...).



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