Advisory ID: DUO-PSA-2014-003
Publication Date: 2014-01-27
Status: Confirmed, Fixed
Document Revision: 2
Duo Security has identified an issue in which it is possible to bypass second factor authentication of Remote Desktop Protocol (RDP) integrations which are GINA-based (e.g. those installed on Windows XP/Server 2003).
The RDP integration works to add two-factor authentication to Windows logins, both Remote Desktop and (optionally) the local console. When the user has provided valid credentials (username and password), the integration presents a second-factor authentication dialog. Under normal operation, when the second-factor authentication is successful, the user is logged on.
However, under certain circumstances (e.g. race conditions involving the user pressing "Ctrl-Alt-Delete" to interrupt a transitory dialog), the GINA framework would return an undocumented error, which was treated as a successful authentication.
Additionally, it was also identified that under these conditions, a thread used by the Duo integration would enter an undefined state. This could potentially lead to a crash in the Winlogon process, resulting in a Denial of Service (“blue screen”) of the host.
A user with valid primary authentication credentials (username and password) may be able to bypass the second factor of authentication.
There is currently no workaround available for this issue.
Duo Security is currently working on an update to these integrations at the end of March 2014 that will cover these new transport mechanisms, to ensure two-factor authentication is enforced on all logins.
Vulnerability Class: Authentication Bypass Issue (CWE-592), Unchecked Error Condition (CWE-391)
Remotely Exploitable: Yes
Authentication Required: Yes/Partial (first factor required; second factor bypassed)
CVSSv2 Overall Score: 7.2
CVSSv2 Group Scores: Base: 4.9, Temporal: 4.7, Environmental: 7.2
CVSSv2 Vector: AV:N/AC:M/Au:S/C:P/I:P/A:N/E:H/RL:W/RC:C/CDP:LM/TD:ND/CR:H/IR:H/AR:ND
Feedback regarding this issue should be sent to firstname.lastname@example.org and reference "DUO-PSA-2014-003" in the subject.