Microsoft updated the Certificate Trust List in Windows to revoke trust for a certificate authority operated by the Indian government after it improperly issued at least 45 SSL certificates for domains owned by Google and Yahoo.
"These SSL certificates could be used to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against web properties," Microsoft said Thursday in a security advisory.
The security incident came into the public spotlight Tuesday when security engineers from Google revealed that on July 2 they identified several certificates for Google domains that had been issued without authorization by the National Informatics Centre (NIC), a branch of the Indian Ministry of Communications and Information Technology.
As part of its mandate to develop and host official government websites, the NIC operated a digital certificate authority (CA) that was subordinated to the Controller of Certifying Authorities (CCA), the Indian government's primary CA.
India's CCA is included in Microsoft's Trusted Root Certification Authorities Store, which means that any SSL (secure sockets layer) certificates issued by itself or its subordinates -- like the NIC -- are trusted by default by many Windows programs, including the Google Chrome and Internet Explorer Web browsers.
An investigation by India's CCA concluded that the NIC's digital certificate issuance process was compromised, resulting in four SSL certificates being improperly issued for Google and Yahoo domains, Google reported Wednesday. However, the company is aware of more than four rogue certificates signed by the NIC, suggesting that the true scope of the breach is unknown.
India CCA and the NIC did not respond to requests sent Thursday for more information about the security breach, but Microsoft's advisory sheds a bit more light on what happened.
According to the company, the NIC improperly issued a subordinate CA certificate and that certificate was then misused to issue SSL certificates for multiple Google and Yahoo sites.
It's not clear to whom and under what circumstances the NIC issued the powerful subordinate CA certificate. Microsoft warns that "the subordinate CA certificate may also have been used to issue certificates for other, currently unknown sites," exposing their users to possible attacks.
The Microsoft update blacklists the NIC's CA certificates, essentially revoking trust in all SSL certificates the NIC has ever issued, including legitimate ones used on some Indian government websites.
The Certificate Trust List (CTL) will be updated automatically on systems running Windows 8, Windows 8.1, Windows RT, Windows RT 8.1, Windows Server 2012 and Windows Server 2012 R2, as well as on devices running Windows Phone 8 or Windows Phone 8.1.
Systems running Windows Vista, Windows 7, Windows Server 2008 or Windows Server 2008 R2 need to have installed an older update called KB2677070 in order to receive automatic updates for revoked certificates.
There is currently no CTL update available for Windows Server 2003 that resolves this issue, but Microsoft plans to release one at a later time.