Microsoft acts to block bogus crypto certificates

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Microsoft acts to block bogus crypto certificates

Warwick Ashford

Microsoft has issued a security advisory about improperly issued SSL-encryption certificates, which could be used in attempts to spoof content, perform phishing attacks or perform man-in-the-middle attacks.

The fraudulent certificates were issued by the National Informatics Centre (NIC) of India, an intermediate certificate authority that is trusted and overseen by India's Controller of Certifying Authorities (CCA).

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The CCA, in turn, is trusted by the Microsoft Root Store, a library that Internet Explorer and many other Windows apps rely on to process the SSL certificates that banks, email providers and other online services use to encrypt traffic and prove their authenticity.

Microsoft said the issue affects all supported releases of Microsoft Windows, but said the company was not currently aware of attacks related to this issue.

The subordinate CA was misused to issue SSL certificates for multiple sites, including Google and Yahoo web properties.

The CCA has reportedly confirmed the bogus certificates were the result of a compromise of NIC's certificate issuance process.

“These SSL certificates could be used to spoof content, perform phishing attacks, or perform man-in-the-middle attacks against web properties,” Microsoft said.

The subordinate CAs may also have been used to issue certificates for other, currently unknown sites, which could be subject to similar attacks, it added.

Windows appears to be the only operating system that will trust the fraudulent certificates, meaning apps running on Mac OS X, Linux, and other platforms are not at risk, according to ars technica.

On Windows, the Firefox browser and the Thunderbird email client were not affected because they rely on a root store that is independent of the Microsoft operating system.

In response to the threat, Microsoft has updated the Certificate Trust list (CTL) for all supported releases of Microsoft Windows to remove the trust of certificates that are causing this issue.

“We have been working diligently on the mis-issued third-party certificates and have untrusted the related Subordinate Certification Authority certificates to ensure our customers remain protected,” said a Microsoft statement emailed to Computer Weekly.

An automatic updater of revoked certificates is included in supported editions of Windows 8, Windows 8.1, Windows RT, Windows RT 8.1, Windows Server 2012, and Windows Server 2012 R2, and for devices running Windows Phone 8 or Windows Phone 8.1.

For these operating systems or devices, Microsoft said users do not need to take any action because the CTL will be updated automatically.

Systems are also protected if they run Windows Vista, Windows 7, Windows Server 2008 or copies of Windows Server 2008 R2 that are using the automatic updater of revoked certificates.

But for systems running Windows Vista, Windows 7, Windows Server 2008 or copies of Windows Server 2008 R2 that do not have the automatic updater of revoked certificates installed, this update is not available.

To receive the update, users must install the automatic updater of revoked certificates.

Users in disconnected environments who are running Windows Vista, Windows 7, Windows 8, Windows Server 2008, Windows Server 2008 R2, or Windows Server 2012 can install update 2813430 to receive this update.

“At this time, no update is available for customers running Windows Server 2003. Microsoft will update this advisory at such time as an update becomes available for Windows Server 2003 customers,” the security advisory said.

Additional protection is offered by the Enhanced Mitigation Experience Toolkit (EMET) 4.1, and newer versions, said Dustin Childs, group manager, response communications at Microsoft.

“EMET will help mitigate man-in-the-middle attacks by detecting untrusted or improperly issued SSL certificates through the Certificate Trust feature,” he wrote in a blog post.

Security researchers said the fake certificates underscores the key risks of using public key infrastructure (PKI) to ensure the authenticity of a remote party.

“The system we use for securing websites is based on the network of trusted certificate authorities and subordinate authorities,” said Craig Young, security researcher at Tripwire.

“When any one of these authorities is controlled by someone with malicious intentions it is possible to impersonate services such as websites, email and file transfer. The malicious possibilities are limitless,” he said.

According to Young, the problem is compounded by the fact computers and SSL systems are designed to trust a long list of authorities.

“We have seen certificate authorities get compromised and used to sign counterfeit certificates several times in the recent past. This is why SSL implementations should always use revocation lists,” he said.

One of the best ways to protect users from this type of threat, said Young, is through the use of pinned certificates.  

This is a deployment in which software is designed to require specific certificates instead of allowing any certificate signed by a 'trusted' authority.

“This practice is used in the Gmail app for Android, for example, but unfortunately this approach does not scale for general web browsing,” said Young.

“To protect themselves from these kinds of incidents users may want to remove trust for regional certificate authorities that aren’t needed in the user's locale,” he said.


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