A maintenance exercise gone awry at root certificate authority GlobalSign caused what could be thousands of websites to be mistakenly treated as insecure by web browsers and therefore become inaccessible to users attempting to reach them.

GlobalSign itself has resolved the issue at its end. But users who visited the affected sites before the problem was resolved could find themselves being blocked until their browser cache expires—a process that could take four or more days.

In an alert this week, GlobalSign described the problem as stemming from its revocation of a cross-certificate linking two root certificates. As a certificate authority that manages several root certificates, GlobalSign provides cross-certificates linking the roots to maximize effectiveness across different platforms, the company said in its alert.

During a scheduled cleanup of some of the links last week, GlobalSign revoked a cross-certificate linking two root certificates. The revoked certificate was included in a Certificate Revocation List (CRL) published Oct. 7.

About a week later, on Oct. 13, when GlobalSign’s delegated Online Certificate Status Protocol (OCSP) responder database was updated, it incorrectly determined that all intermediate or downstream certificates associated with the root had been revoked as well, along with the cross certificate.

This caused browsers that use OCSP to determine the revocation status of digital certificates, to treat thousands of websites using the “revoked” certificates as untrustworthy and in some cases preventing access to the sites.

In an update on the issue posted Friday, GlobalSign said it uses a third-party OCSP responder system for relaying information about the status of its certificates.

“However, and unfortunately for our ecosystem and our stakeholders and their customers, the logic within the responder code base determined that the revocation of the Cross Certificate … was effectively an instruction to also identify all other subordinate certificate authorities,” as bad, the company said.

“We made a couple of incorrect assumptions,” in revoking the cross-certificate linking two roots, says Steve Roylance, strategic products director at GlobalSign, in comments to Dark Reading.

When revoking the certificate, GlobalSign had no idea that the OCSP server would push out responses indicating intermediate certificates had been revoked, he said. “That was unfortunate and not something that was expected,” Roylance says. “It came as a surprise to us,” Roylance says. He added that it is not possible to say how many websites might have been affected by the mix-up.

Since discovering the problem, GlobalSign has removed the cross-certificate from the OCSP database and cleared all caches and made new intermediate certificates available to customers, the company said. However, some end users could continue to experience difficulties accessing affected websites since their browser caches would still show the sites as being untrustworthy. In such situations, the problems will resolve in about four days when the caches refresh, the company said.

Kevin Bocek, vice president of security strategy and threat intelligence at Venafi, says GlobalSign’s customers too could run into problems installing the newly issued intermediate certificates.

“Do security operations teams know they use GlobalSign? Do they know where the servers that use GlobalSign are located?” he says. “Do they know how to add new CA certificates to application truststores,” he said noting differences in the process for doing so between different applications like WebSphere, Microsoft IIS, and Apache.

“In our experience, most organizations do not have this visibility and are unable to quickly locate and change out certificates,” he says.

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