Security Advisory
Microsoft Security Advisory 2524375
Fraudulent Digital Certificates Could Allow Spoofing
Published: March 23, 2011 | Updated: July 06, 2011
Version: 5.0
General Information
Executive Summary
Microsoft is aware of nine fraudulent digital certificates issued by Comodo, a certification authority present in the Trusted Root Certification Authorities Store, on all supported releases of Microsoft Windows, Windows Mobile 6.x, Windows Phone 7, Microsoft Kin, and Zune HD devices. Comodo advised Microsoft on March 16, 2011 that nine certificates had been signed on behalf of a third party without sufficiently validating its identity. These certificates may be used to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against all Web browser users including users of Internet Explorer.
These certificates affect the following Web properties:
- login.live.com
- mail.google.com
- www.google.com
- login.yahoo.com (3 certificates)
- login.skype.com
- addons.mozilla.org
- "Global Trustee"
Comodo has revoked these certificates, and they are listed in Comodo’s current Certificate Revocation List (CRL). In addition, browsers which have enabled the Online Certificate Status Protocol (OCSP) will interactively validate these certificates and block them from being used.
An update to help address this issue is available for all supported releases of Windows, Windows Mobile 6.x devices, and Zune HD devices. As of May 3, 2011, the update is also beginning to be delivered to Windows Phone 7 customers. For more information about this update, see Microsoft Knowledge Base Article 2524375.
For supported releases of Microsoft Windows, typically no action is required of customers to install this update, because the majority of customers have automatic updating enabled and this update will be downloaded and installed automatically. For more information, including how to manually install this update and how to install the update on Windows Mobile 6.x, Windows Phone 7, and Zune HD devices, see the Suggested Actions section of this advisory.
Advisory Details
Issue References
For more information about this issue, see the following references:
| References | Identification |
|---|---|
| Microsoft Knowledge Base Article | 2524375 |
Affected Software and Devices
This advisory discusses the following software and devices.
| Affected Software |
|---|
| Windows XP Service Pack 3 |
| Windows XP Professional x64 Edition Service Pack 2 |
| Windows Server 2003 Service Pack 2 |
| Windows Server 2003 x64 Edition Service Pack 2 |
| Windows Server 2003 with SP2 for Itanium-based Systems |
| Windows Vista Service Pack 1 and Windows Vista Service Pack 2 |
| Windows Vista x64 Edition Service Pack 1 and Windows Vista x64 Edition Service Pack 2 |
| Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2* |
| Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2* |
| Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2 |
| Windows 7 for 32-bit Systems and Windows 7 for 32-bit Systems Service Pack 1 |
| Windows 7 for x64-based Systems and Windows 7 for x64-based Systems Service Pack 1 |
| Windows Server 2008 R2 for x64-based Systems and Windows Server 2008 R2 for x64-based Systems Service Pack 1* |
| Windows Server 2008 R2 for Itanium-based Systems and Windows Server 2008 R2 for Itanium-based Systems Service Pack 1 |
| Affected Devices |
| Windows Mobile 6.x |
| Windows Phone 7 |
| Microsoft Kin |
| Zune HD 16GB, Zune HD 32GB, and Zune HD 64GB |
*Server Core installation affected. This update applies, with the same severity rating, to supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, whether or not installed using the Server Core installation option. For more information on this installation option, see the TechNet articles, Managing a Server Core Installation and Servicing a Server Core Installation. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008 and Windows Server 2008 R2; see Compare Server Core Installation Options.
| Non-Affected Devices |
|---|
| Zune 4GB, Zune 8GB, Zune 16GB, Zune 30GB, Zune 80GB, and Zune 120GB |
Frequently Asked Questions
Why was this advisory revised July 6, 2011?
Microsoft revised this advisory to announce the release of the update to address the SSL security issue for Zune HD devices. To install the update, Zune HD customers must connect their device to a computer and use the Zune PC client to complete the update process. For more information and instructions, see Microsoft Knowledge Base Article 2524375.
The update for Microsoft Kin is unavailable at this time. Microsoft will issue an update for this device when testing is complete, to ensure a high degree of quality for its release.
Why were Zune 4GB, Zune 8GB, Zune 16GB, Zune 30GB, Zune 80GB, and Zune 120GB devices removed from the Affected Software and Devices table?
After careful review of the attack vector, Microsoft has determined that the chance of exploiting this issue on these Zune devices is extremely low due to the fact that these devices do not have a Web browser. As a result, Zune 4GB, Zune 8GB, Zune 16GB, Zune 30GB, Zune 80GB, and Zune 120GB will not receive an update and were moved to the Non-Affected Devices table.
Why was this advisory revised May 10, 2011?
Microsoft revised this advisory to announce the release of an update for Windows Mobile 6.x devices. The update is available for download on the Microsoft Download Center. For more information, see Microsoft Knowledge Base Article 2524375.
The updates for Microsoft Kin and Zune devices are unavailable at this time. Microsoft will issue updates for these devices when testing is complete, to ensure a high degree of quality for their release.
Why was this advisory revised May 3, 2011?
Microsoft revised this advisory to announce the release of an update for Windows Phone 7 devices. At the time of release, the update is not available for all Windows Phone 7 customers; instead, customers will receive an on-device notification once the update is available for their phone. To learn more or to install the update, Windows Phone 7 customers will have to connect their phone to a computer and use the Zune PC client or Windows Phone 7 Connector (for Mac) to complete the update process. For more information, see Microsoft Knowledge Base Article 2524375.
The updates for Windows Mobile 6.x, Microsoft Kin, and Zune devices are unavailable at this time. Microsoft will issue updates for these devices when testing is complete, to ensure a high degree of quality for their release.
Why was this advisory revised April 19, 2011?
Microsoft revised this advisory to add Windows Mobile 6.x, Windows Phone 7, Microsoft Kin, and Zune devices to affected software and devices. Microsoft is aware that the local untrusted certificate store on these devices needs to be updated to include the nine fraudulent digital certificates.
The updates for Windows Mobile 6.x, Windows Phone 7, Microsoft Kin, and Zune devices are unavailable at this time. Microsoft will issue updates for these devices when testing is complete, to ensure a high degree of quality for their release.
What is cryptography?
Cryptography is the science of securing information by converting it between its normal, readable state (called plaintext) and one in which the data is obscured (known as ciphertext).
In all forms of cryptography, a value known as a key is used in conjunction with a procedure called a crypto algorithm to transform plaintext data into ciphertext. In the most familiar type of cryptography, secret-key cryptography, the ciphertext is transformed back into plaintext using the same key. However, in a second type of cryptography, public-key cryptography, a different key is used to transform the ciphertext back into plaintext.
What is a digital certificate?
In public-key cryptography, one of the keys, known as the private key, must be kept secret. The other key, known as the public key, is intended to be shared with the world. However, there must be a way for the owner of the key to tell the world who the key belongs to. Digital certificates provide a way to do this. A digital certificate is a tamperproof piece of data that packages a public key together with information about it - who owns it, what it can be used for, when it expires, and so forth.
What are certificates used for?
Certificates are used primarily to verify the identity of a person or device, authenticate a service, or encrypt files. Normally you won’t have to think about certificates at all. You might, however, see a message telling you that a certificate is expired or invalid. In those cases you should follow the instructions in the message.
What is a certification authority (CA)?
Certification authorities are the organizations that issue certificates. They establish and verify the authenticity of public keys that belong to people or other certification authorities, and they verify the identity of a person or organization that asks for a certificate.
What caused the issue?
Comodo, a major certification authority, has informed Microsoft that several digital certificates have been issued without sufficiently validating their identity. These certificates could be used to spoof the identity of services, tricking users into trusting them.
Note Comodo has revoked these certificates, and they are listed in Comodo’s current Certificate Revocation List (CRL).
What might an attacker use the vulnerability to do?
An attacker could use these certificates to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against all Web browser users including users of Internet Explorer.
What is a man-in-the-middle attack?
A man-in-the-middle attack occurs when an attacker reroutes communication between two users through the attacker’s computer without the knowledge of the two communicating users. Each user in the communication unknowingly sends traffic to and receives traffic from the attacker, all the while thinking they are communicating only with the intended user.
What is the procedure for revoking a certificate?
There is a standard procedure that should allow Comodo to prevent these certificates from being accepted if they are used. Every certificate issuer periodically generates a CRL, which lists all the certificates that should be considered invalid. Every certificate should provide a piece of data called the CRL Distribution Point (CDP) that indicates the location where the CRL can be obtained.
An alternative way for Web browsers to validate the identity of a digital certificate is by using the Online Certificate Status Protocol (OCSP). OCSP allows interactive validation of a certificate by connecting to an OCSP responder, hosted by the Certificate Authority (CA) which signed the digital certificate. Every certificate should provide a pointer to the OCSP responder location through the Authority Information Access (AIA) extension in the certificate. In addition, OCSP stapling allows the Web server itself to provide an OCSP validation response to the client.
OCSP validation is enabled by default on Internet Explorer 7 and later versions of Internet Explorer on supported editions of Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2. On these operating systems, if the OCSP validation check fails, the browser will validate the certificate by contacting the CRL Location.
For more information on certificate revocation checking, see the TechNet article, Certificate Revocation and Status Checking.
What is a Certificate Revocation List (CRL)?
CRL is a digitally signed list, issued by a CA, that contains a list of certificates issued by the CA and subsequently revoked by the CA. For each individual revoked certificate, the listing includes the serial number of the certificate, the date that the certificate was revoked, and the revocation reason. Applications can perform CRL checking to determine a presented certificate’s revocation status.
What is CRL Distribution Point (CDP)?
CDP is a certificate extension that indicates where the certificate revocation list for a CA can be retrieved. It can contain none, one, or many HTTP, file, or LDAP URLs.
What is Online Certificate Status Protocol (OCSP)?
OCSP is a protocol that allows real-time validation of a certificate’s status. Typically, an OCSP responder replies with the revocation status based on the CRL retrieved from the CA.
What is Microsoft doing to help with resolving this issue?
Although this issue does not result from an issue in any Microsoft product, we have nevertheless developed an update that will help to protect customers by ensuring that these nine fraudulent certificates are always treated as untrusted.
If there is no issue in Microsoft software, why is Microsoft releasing an update?
Even when CRL and OCSP validation is enabled, validation techniques are not sufficiently robust to guarantee that users are protected against malicious use of these certificates. When the CRL location and OCSP responder can be reached, validation checks are highly reliable and effective.
However, when certificate revocation checks fail due to network and connectivity issues, browsers and other client applications, including Internet Explorer, may ignore these errors and consider the certificate trustworthy due to the lack of proof otherwise. In these scenarios, customers may still be affected.
**What does the update do? ** The update for supported releases of Microsoft Windows addresses the issue by placing the nine fraudulent certificates into the local untrusted certificate store of Microsoft Windows. The updates for Windows Mobile 6.x, Windows Phone 7, and Zune HD devices address the issue by placing the nine fraudulent certificates into the local untrusted certificate store on the device. The update for Microsoft Kin is unavailable at this time.
How do I know if I’ve encountered an invalid certificate error?
When Internet Explorer encounters an invalid certificate, users are presented with a Web page that says, "There is a problem with this website’s security certificate." Users are encouraged to close the Web page and navigate away from the site when this warning message appears.
Users are only presented this message when the certificate is determined to be invalid, for instance when the user has Certificate Revocation List (CRL) or Online Certificate Status Protocol (OCSP) validation enabled. OCSP validation is enabled by default on Internet Explorer 7 and later versions of Internet Explorer on supported editions of Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.
After applying the update, how can I verify the certificates in the Untrusted Certificates folder?
For information on how to view certificates, see the MSDN article How to: View Certificates with the MMC Snap-in.
In the Certificates MMC snap-in, verify that the following certificates have been added to the Untrusted Certificates folder:
| Certificate | Issued by | Serial Number |
|---|---|---|
| addons.mozilla.org | UTN-USERFirst-Hardware | 00 92 39 d5 34 8f 40 d1 69 5a 74 54 70 e1 f2 3f 43 |
| “Global Trustee” | UTN-USERFirst-Hardware | 00 d8 f3 5f 4e b7 87 2b 2d ab 06 92 e3 15 38 2f b0 |
| login.live.com | UTN-USERFirst-Hardware | 00 b0 b7 13 3e d0 96 f9 b5 6f ae 91 c8 74 bd 3a c0 |
| login.skype.com | UTN-USERFirst-Hardware | 00 e9 02 8b 95 78 e4 15 dc 1a 71 0a 2b 88 15 44 47 |
| login.yahoo.com | UTN-USERFirst-Hardware | 00 d7 55 8f da f5 f1 10 5b b2 13 28 2b 70 77 29 a3 |
| login.yahoo.com | UTN-USERFirst-Hardware | 39 2a 43 4f 0e 07 df 1f 8a a3 05 de 34 e0 c2 29 |
| login.yahoo.com | UTN-USERFirst-Hardware | 3e 75 ce d4 6b 69 30 21 21 88 30 ae 86 a8 2a 71 |
| mail.google.com | UTN-USERFirst-Hardware | 04 7e cb e9 fc a5 5f 7b d0 9e ae 36 e1 0c ae 1e |
| www.google.com | UTN-USERFirst-Hardware | 00 f5 c8 6a f3 61 62 f1 3a 64 f5 4f 6d c9 58 7c 06 |
Suggested Actions
Install the update
An update is available to help address this issue.
For supported releases of Microsoft Windows
The majority of customers have automatic updating enabled and will not need to take any action because this update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.
For administrators and enterprise installations, or end users who want to install this update manually, Microsoft recommends that customers apply the update immediately using update management software, or by checking for updates using the Microsoft Update service.
The update is also available from the Microsoft Download Center; see Microsoft Knowledge Base Article 2524375 for download links.
For Windows Phone 7 devices
At the time of release, the update is not available for all Windows Phone 7 customers; instead, customers will receive an on-device notification once the update is available for their phone. To learn more or to install the update, Windows Phone 7 customers will have to connect their phone to a computer and use the Zune PC client or Windows Phone 7 Connector (for Mac) to complete the update process. For more information about the update, see Microsoft Knowledge Base Article 2524375.
To update the Zune PC client, customers can configure automatic updating to check online for updates from Microsoft Update by using the Microsoft Update service. Customers who have automatic updating enabled and configured to check online for updates from Microsoft Update typically will not need to take any action to update their Zune software because this update will be downloaded and installed automatically.
For Windows Mobile 6.x devices
The update is available for download from the Microsoft Download Center. For more information about the update and download links, see Microsoft Knowledge Base Article 2524375.
For Zune HD devices
The update is available through the Zune PC client. The update is applied when the Zune HD device is connected to the updated Zune software. For more information about the update, see Microsoft Knowledge Base Article 2524375.
To update the Zune PC client, customers can configure automatic updating to check online for updates from Microsoft Update by using the Microsoft Update service. Customers who have automatic updating enabled and configured to check online for updates from Microsoft Update typically will not need to take any action to update their Zune software because this update will be downloaded and installed automatically.
Additional Suggested Actions
Review the Microsoft Knowledge Base Article that is associated with this advisory
For more information about this issue, see Microsoft Knowledge Base Article 2524375.
Protect your PC
We continue to encourage customers to follow our Protect Your Computer guidance of enabling a firewall, getting software updates and installing antivirus software. Customers can learn more about these steps by visiting Protect Your Computer.
For more information about staying safe on the Internet, visit Microsoft Security Central.
Keep Microsoft Software Updated
Users running Microsoft software should apply the latest Microsoft security updates to help make sure that their computers are as protected as possible. If you are not sure whether your software is up to date, visit Microsoft Update, scan your computer for available updates, and install any high-priority updates that are offered to you. If you have automatic updating enabled and configured to provide updates for Microsoft products, the updates are delivered to you when they are released, but you should verify that they are installed.
Other Information
Microsoft Active Protections Program (MAPP)
To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please visit the active protections Web sites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.
Feedback
- You can provide feedback by completing the Microsoft Help and Support form, Customer Service Contact Us.
Support
- Customers in the United States and Canada can receive technical support from Security Support. For more information about available support options, see Microsoft Help and Support.
- International customers can receive support from their local Microsoft subsidiaries. For more information about how to contact Microsoft for international support issues, visit International Support.
- Microsoft TechNet Security provides additional information about security in Microsoft products.
Disclaimer
The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
Revisions
- V1.0 (March 23, 2011): Advisory published.
- V2.0 (April 19, 2011): Added Windows Mobile 6.x, Windows Phone 7, Microsoft Kin, and Zune devices to affected software and devices.
- V3.0 (May 3, 2011): Announced the release of an update for Windows Phone 7 devices. The update is not available to all customers at the time of release; see the advisory FAQ for more information.
- V4.0 (May 10, 2011): Announced the release of an update for Windows Mobile 6.x devices.
- V5.0 (July 6, 2011): Announced the release of an update for Zune HD devices and moved Zune devices to the Non-Affected Devices table.
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