Microsoft Security Advisory 3123040
Inadvertently Disclosed Digital Certificate Could Allow Spoofing
Published: December 8, 2015
Microsoft is aware of an SSL/TLS digital certificate for *.xboxlive.com for which the private keys were inadvertently disclosed. The certificate could be used in attempts to perform man-in-the-middle attacks. It cannot be used to issue other certificates, impersonate other domains, or sign code. This issue affects all supported releases of Microsoft Windows. Microsoft is not currently aware of attacks related to this issue.
To help protect customers from potentially fraudulent use of the SSL/TLS digital certificate, the certificate has been deemed no longer valid and Microsoft is updating the Certificate Trust list (CTL) for all supported releases of Microsoft Windows to remove the trust of the certificate. For more information about the certificate, see the Frequently Asked Questions section of this advisory.
Recommendation. An automatic updater of certificate trust lists is included in supported editions of Windows 8, Windows 8.1, Windows RT, Windows RT 8.1, Windows Server 2012, Windows Server 2012 R2, Windows 10, and Windows 10 Version 1511, and for devices running Windows Phone 8, Windows Phone 8.1, and Windows 10 Mobile. For these operating systems and devices, customers do not need to take any action as these systems and devices will be automatically protected.
For systems running Windows Vista, Windows 7, Windows Server 2008, or Windows Server 2008 R2 that are using the automatic updater of certificate trust lists (see Microsoft Knowledge Base Article 2677070 for details), customers do not need to take any action as these systems will be automatically protected.
This advisory discusses the following software.
|Windows Vista Service Pack 2|
|Windows Vista x64 Edition Service Pack 2|
|Windows Server 2008 for 32-bit Systems Service Pack 2|
|Windows Server 2008 for x64-based Systems Service Pack 2|
|Windows Server 2008 for Itanium-based Systems Service Pack 2|
|Windows 7 for 32-bit Systems Service Pack 1|
|Windows 7 for x64-based Systems Service Pack 1|
|Windows Server 2008 R2 for x64-based Systems Service Pack 1|
|Windows Server 2008 R2 for Itanium-based Systems Service Pack 1|
|Windows 8 for 32-bit Systems|
|Windows 8 for x64-based Systems|
|Windows 8.1 for 32-bit Systems|
|Windows 8.1 for x64-based Systems|
|Windows RT 8.1|
|Windows Server 2012|
|Windows Server 2012 R2|
|Windows 10 Version 1511|
|Server Core installation option|
|Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation)|
|Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation)|
|Windows Server 2008 R2 for x64-based Systems (Server Core installation)|
|Windows Server 2012 (Server Core installation)|
|Windows Server 2012 R2 (Server Core installation)|
|Windows Phone 8|
|Windows Phone 8.1|
|Windows 10 Mobile|
What is the scope of the advisory?
The purpose of this advisory is to notify customers that the private keys for an SSL/TLS digital certificate for *xboxlive.com have been inadvertently disclosed. The SSL/TLS certificate could be used to perform man-in-the-middle attacks against Xbox Live customers.
What caused the issue?
The issue was caused by the inadvertent disclosure of private key information for a cryptographic certificate for *.xboxlive.com.
Does this update address any other digital certificates?
Yes, in addition to addressing the certificate described in this advisory, this update is cumulative and includes digital certificates described in previous advisories:
- Microsoft Security Advisory 2982792
- Microsoft Security Advisory 2916652
- Microsoft Security Advisory 2798897
- Microsoft Security Advisory 2728973
- Microsoft Security Advisory 2718704
- Microsoft Security Advisory 2641690
- Microsoft Security Advisory 2607712
- Microsoft Security Advisory 2524375
- Microsoft Security Advisory 3046310
- Microsoft Security Advisory 3119884
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 is a Certificate Trust List (CTL)?
A trust must exist between the recipient of a signed message and the signer of the message. One method of establishing this trust is through a certificate, an electronic document verifying that entities or persons are who they claim to be. A certificate is issued to an entity by a third party that is trusted by both of the other parties. So, each recipient of a signed message decides if the issuer of the signer's certificate is trustworthy. CryptoAPI has implemented a methodology to allow application developers to create applications that automatically verify certificates against a predefined list of trusted certificates or roots. This list of trusted entities (called subjects) is called a certificate trust list (CTL). For more information, please see the MSDN article, Certificate Trust Verification.
What might an attacker do with these certificates?
An attacker could use these certificates to perform man-in-the-middle attacks against *.xboxlive.com properties.
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 Microsoft doing to help with resolving this issue?
Although this issue does not result from an issue in any Microsoft product, we are nevertheless updating the CTL and providing an update to help protect customers. Microsoft will continue to investigate this issue and may make future changes to the CTL or release a future update to help protect customers.
After applying the update, how can I verify the certificates in the Microsoft Untrusted Certificates Store?
For Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2 systems that are using the automatic updater of certificate trust lists (see Microsoft Knowledge Base Article 2677070 for details), and for Windows 8, Windows 8.1, Windows RT, Windows RT 8.1, Windows Server 2012, Windows Server 2012 R2, Windows 10, and Windows 10 Version 1511 systems, you can check the Application log in the Event Viewer for an entry with the following values:
- Source: CAPI2
- Level: Information
- Event ID: 4112
- Description: Successful auto update of disallowed certificate list with effective date: Tuesday, December 1, 2015 (or later).
For systems not using the automatic updater of certificate trust lists, in the Certificates MMC snap-in, verify that the following certificate has been added to the Untrusted Certificates folder:
|xboxlive.com||Microsoft IT SSL SHA2||8b 2e 65 a5 da 17 fc cc bc de 7e f8 7b 0c 0e d5 d0 70 1f 9f|
- You can provide feedback by completing the Microsoft Help and Support form, Customer Service Contact Us.
- Customers in the United States and Canada can receive technical support from Security Support. For more information, see Microsoft Help and Support.
- International customers can receive support from their local Microsoft subsidiaries. For more information, see International Support.
- Microsoft TechNet Security provides additional information about security in Microsoft products.
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.
- V1.0 (December 8, 2015): Advisory published.
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