On June 17, 2015 a few vulnerabilities were discovered in Drupal core that affect versions 6.x and 7.x The vulnerabilities discovered are Impersonation, Open Redirect, and Information Disclosure. The information below was provided by the Drupal Security Advisories page.
Impersonation (OpenID module – Drupal 6 and 7 – Critical)
A vulnerability was found in the OpenID module that allows a malicious user to log in as other users on the site, including administrators, and hijack their accounts.
This vulnerability is mitigated by the fact that the victim must have an account with an associated OpenID identity from a particular set of OpenID providers (including, but not limited to, Verisign, LiveJournal, or StackExchange).
Open redirect (Field UI module – Drupal 7 – Less critical)
The Field UI module uses a “destinations” query string parameter in URLs to redirect users to new destinations after completing an action on a few administration pages. Under certain circumstances, malicious users can use this parameter to construct a URL that will trick users into being redirected to a 3rd party website, thereby exposing the users to potential social engineering attacks.
This vulnerability is mitigated by the fact that only sites with the Field UI module enabled are affected.
Drupal 6 core is not affected, but see the similar advisory for the Drupal 6 contributed CCK module: SA-CONTRIB-2015-126
Open redirect (Overlay module – Drupal 7 – Less critical)
This vulnerability is mitigated by the fact that it can only be used against site users who have the “Access the administrative overlay” permission, and that the Overlay module must be enabled.
Information disclosure (Render cache system – Drupal 7 – Less critical)
On sites utilizing Drupal 7’s render cache system to cache content on the site by user role, private content viewed by user 1 may be included in the cache and exposed to non-privileged users.
This vulnerability is mitigated by the fact that render caching is not used in Drupal 7 core itself (it requires custom code or the contributed Render Cache module to enable) and that it only affects sites that have user 1 browsing the live site. Exposure is also limited if an administrative role has been assigned to the user 1 account (which is done, for example, by the Standard install profile that ships with Drupal core).
The solution is simple as the Drupal team has implemented a new patch for each version. Simply upgrade to the latest subversion for each major version. If you are on Drupal 6, upgrade to 6.36 and if you are on version 7 upgrade to 7.38.