Microsoft Office 365 Outlook - CS Redirect Vulnerability

Type vulnerlab
Reporter Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (
Modified 2013-05-26T00:00:00


                                            Document Title:
Microsoft Office 365 Outlook - CS Redirect Vulnerability

References (Source):

Microsoft Security Response Center (MSRC) ID: 14091
Microsoft Security Response Center (MSRC) MANAGER: JT

Release Date:

Vulnerability Laboratory ID (VL-ID):

Common Vulnerability Scoring System:

Product & Service Introduction:
Office 365 primarily denotes a set of subscription based software services that require monthly or periodic payment 
of fees to Microsoft Corporation. By contrast, Office 20XX generally refers to a suite of desktop applications that 
alone by themselves are not subscription based and do not carry monthly fees.

Although Office 365 also often refers to cloud-based services rather than desktop applications, certain Office 365 
subscription plans include a subscription to Office 20XX desktop applications in addition to cloud-based services. 
The subscription to Office 20XX desktop applications, by virtue of the subscription, makes the subscription part of 
an Office 365 offering.

Office 365 was initially announced in the autumn of 2010, and was made available to the public on June 28, 2011. 
The initial subscription plans included a Professional plan (for organizations of 25 and smaller) and an Enterprise 
plan (for organizations with more individuals). Microsoft also offers a Dedicated and ITAR subscription model for 
large companies. The Office 365 Dedicated offering isolates servers to be used for only a single customer while 
ITAR (AKA Federal) offers a higher level of security (individual background checks and extremely-limited access to 
sensitive parts of the system by knowledge workers) that complies with the ITAR standard.

Depending on the subscription plan, Office 365 can include a subscription to Office 20XX desktop applications, in 
addition to hosted versions of Microsoft`s Server products (including Exchange Server, SharePoint Server, and Lync Server) 
that are delivered and accessed over the Internet, in effect, the next version of Business Productivity Online Suite (BPOS).
In December 2011, Microsoft launched Trust Center and announced that Office 365 now complies with EU privacy regulations.

(Copy of the Homepage:

Abstract Advisory Information:
The Vulnerability Laboratory Research Team discovered a redirect vulnerability in the Microsoft (cloud-based) Office 365 & bound Outlook Application.

Vulnerability Disclosure Timeline:
2013-02-03:	Researcher Notification & Coordination
2013-02-06:	Vendor Notification
2013-02-07:	Vendor Response/Feedback
2013-05-22:	Vendor Fix/Patch
2013-05-24:	Public Disclosure

Discovery Status:

Affected Product(s):
Microsoft Corp.
Product: Office 365 (cloud-based)

Exploitation Technique:

Severity Level:

Technical Details & Description:
An unauthorized client side redirect web vulnerability is detected in the official Microsoft (cloud-based) Office 365 Applicaiton 
and the bound Outlook service application. The vulnerability allows remote attackers to force unauthorized client side request to external targets.

The vulnerability is located in the `redir.aspx` file when processing to request the bound vulnerable `URL` application. Remote attackers can form 
own malicious links with client side requests to redirect a victim to an external website or malware. The vulnerability can be exploited with a 
required not expired cloud application session of office 365 and low or medium user interaction. An application user account is not required for 
successful exploitation.

Successful exploitation of the vulnerability result in client side external redirects, unauthorized local url loads & client side external malware loads.

Vulnerable Section(s):
                                [+] Microsoft Corp - Office 365 (cloud-based) Application - Outlook Application

Vulnerable File(s):
                                [+] redir.aspx

Vulnerable Parameter(s):
                                [+] URL

Affected Service(s):
                                [+] Office 365 - Cloud

Affected bound Service(s):
                                [+] Outlook (Web)

Proof of Concept (PoC):
The client side redirect vulnerability via url parameter can be exploited by remote attackers without privileged application user account and 
with low or medium required user interaction. For demonstration or reproduce ...


Manipulated (Example):[PATH]/[FILE].[ASPX]?[PARAM]=[EXTERNAL REDIRECT]


Solution - Fix & Patch:
The vulnerability can be patched by implementation of a whitelisting when processing to request the urls of the office 365 cloud service.
Bind the session token when processing to request via GET to the redir function to disallow external (client-side) redirects.

Security Risk:
The security risk of the minor priority (client side) redirect vulnerability is estimated as low.

Credits & Authors:
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (

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