Microsoft has issued an advisory to notify customers that the private keys for an SSL/TLS digital certificate for *xboxlive.com have been disclosed.

According to a security advisory published by Microsoft, the company is propagating a new certificate for the *.xboxlive.com domain because it has “inadvertently disclosed” the certificate’s contents.

Microsoft confirmed the accidental disclosure of the digital certificate private keys for the above domain, a circumstance that opens customers to man-in-the-middle attacks, although the certificate “cannot be used to issue other certificates, impersonate other domains, or sign code”.

The Xboxlive certificate is included in all supported releases of Microsoft Windows.

“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. ” reads the Microsoft advisory.

Microsoft confirmed that revocation of the Xboxlive SSL server certificates should propagate to everybody automatically, however. The company hasn’t provided additional information on how many people may have seen the certificate, but it is unlike that the accidental disclosure has been exploited in attacks in the wild.

Users of Windows have nothing to do, meanwhile users of Vista, Windows 7, Windows Server 2008 or Windows Server 2008 R2 will need to enable the automatic certificate updater.

Users not covered by the automatic update should add the compromised certificate to the list of untrusted certificates by using the Certificates MMC snap-in.

After applying the update, how can users 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, users 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:

Certificate	Issued by	Thumbprint
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

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Pierluigi Paganini

(Security Affairs – Xboxlive certificate, PKI)

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