Microsoft blacklists all DigiNotar certificates

Microsoft counters active attacks by banning the certificate authority and the fraudulent digital certificates

Microsoft on Tuesday blacklisted all DigiNotar certificates after seeing active attacks from at least one fraudulent digital certificate issued by DigiNotar. The company has released updates for all versions of Windows with the new blacklisted data.

DigiNotar is a certification authority that is a member of the Trusted Root Certification Authorities Store. Last week, Dutch authorities and others revealed that hackers had perpetrated a massive theft of more than 500 SSL certificates in July, including several that could attempt to impersonate Microsoft's update services.

BACKGROUND: Comodo hacker claims credit for DigiNotar attack

"Based on our investigation, we've deemed all DigiNotar certificates to be untrustworthy and have moved them to the Untrusted Certificate Store," wrote Dave Forstrom, director of trustworthy computing, on the Microsoft Security Response Center blog. "Additionally, we have extended our support with this update so all customers using Windows XP, Windows Server 2003, and all Windows supported third-party applications are protected."

With 500 spoofed certificates "pwn'd" by the bad guys, Microsoft wasn't the only vendor affected. Last week the TOR Project site, also affected, released a list of all the affected websites in a blog post, and all of the CAs it found to be hosting the hacked certificates. DigiNotar released fake certificates that affected websites and services from Google, Skype, the CIA, Yahoo, Twitter, TOR, Facebook, WordPress, Windows Live, Mozilla and a number of others.

Microsoft, Google and Mozilla all acted quickly to revoke the spoofed certificates so their browsers would reject them. On Sunday, Microsoft assured its customers that the spoofed Microsoft Update certificates could not be used to install malware through Windows Update.

"Attackers are not able to leverage a fraudulent Windows Update certificate to install malware via the Windows Update servers," said Jonathan Ness, an engineer with the Microsoft Security Response Center (MSRC), in a Sunday blog post. "The Windows Update client will only install binary payloads signed by the actual Microsoft root certificate, which is issued and secured by Microsoft."

Seven of the 531 fraudulent certificates were for Microsoft-related domains including update.microsoft.com and windowsupdate.com, while another six were for *.microsoft.com, and another 17 were for live.com, Microsoft's Windows Live social network and collaboration site.

Microsoft recommends that enterprise users not using Microsoft's automatic updating service immediately install the updates. This includes a rare update for Windows Server 2008 Server Core, which is also affected.

However, more industrywide action may be needed, and Microsoft says it "has been actively collaborating with certificate authorities, governments, and software vendors to help protect our mutual customers."

This is because "the most egregious certs issued were for *.*.com and *.*.org while certificates for Windows Update and certificates for other hosts are of limited harm by comparison," according to the TOR Project blog. "The attackers also issued certificates in the names of other certificate authorities such as 'VeriSign Root CA' and 'Thawte Root CA' as we witnessed with ComodoGate, although we cannot determine whether they succeeded in creating any intermediate CA certs."

UPDATED: The TOR project has also named two other CAs that should be blacklisted for hosting fraudulent certificates, Koninklijke Notariele Beroepsorganisatie CA and Stichting TTP Infos CA. Microsoft says that these CAs will also be blocked by today's software updates, even though they are not mentioned by name in its Security Advisory. Forstrom explained in an e-mail to Network World, "Koninklijke Notariele Beroepsorganisatie CA and Stichting TTP Infos CA are two sub-CAs below the DigiNotar CA and therefore blocked as well. In addition, they are not present on the Windows Certificate Trust List and, therefore would not be trusted by Windows."

Julie Bort is the editor of Network World's Open Source community. She also writes the Source Seeker blog, the Odds and Ends blog for Cisco Subnet and the Microsoft Update blog for Microsoft Subnet. Follow Bort on Twitter @Julie188.

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