A security researcher has unearthed evidence showing that three browser-trusted certificate authorities (CAs) owned and operated by Symantec improperly issued more than 100 unvalidated transport layer security certificates. In some cases, those certificates made it possible to spoof HTTPS-protected websites.

One of the most fundamental requirements Google and other major browser developers impose on CAs is that they issue certificates only to people who verify the rightful control of an affected domain name or company name. On multiple occasions last year and earlier this month, the Symantec-owned CAs issued 108 credentials that violated these strict industry guidelines, according to research published Thursday by Andrew Ayer, a security researcher and founder of a CA reseller known as SSLMate. These guidelines were put in place to ensure the integrity of the entire encrypted Web. Nine of the certificates were issued without the permission or knowledge of the affected domain owners. The remaining 99 certificates were issued without proper validation of the company information in the certificate.

Further Reading Symantec employees fired for issuing rogue HTTPS certificate for Google

Many of the improperly issued certificates—which contained the string "test" in various places in a likely indication that they were created for test purposes—were revoked within an hour of being issued. Still, the move represents a major violation by Symantec, which in 2015 fired an undisclosed number of CA employees for doing much the same thing

Even when CA-issued certificates are discovered as fraudulent and revoked, they can still be used to force browsers to verify an impostor site. The difficulty browsers have in blacklisting revoked certificates in real-time is precisely why industry rules strictly control the issuance of such credentials. There's no indication that the unauthorized certificates were ever used in the wild, but there's also no way to rule out that possibility, however remote it is.

"Chrome doesn't [immediately] check certificate revocation, so a revoked certificate can be used in an attack just as easily as an unrevoked certificate," Ayer told Ars. "By default, other browsers fail open and accept a revoked certificate as legitimate if the attacker can successfully block the browser from contacting the revocation server."

("Fail open" is a term that means the browser automatically accepts the certificate in the event the browser can't access the revocation list.)

The nine certificates issued without the domain name owners' permission affected 15 separate domains, with names including wps.itsskin.com, example.com, test.com, test1.com, test2.com, and others. Three Symantec-owned CAs—known as Symantec Trust Network, GeoTrust Inc., and Thawte Inc.—issued the credentials on July 14, October 26, and November 15. The other 99 certificates were issued on many dates between October 21 and January 18. In an e-mail, a Symantec spokeswoman wrote:

"Symantec has learned of a possible situation regarding certificate mis-issuance involving Symantec and other certificate authorities. We are currently gathering the facts about this situation and will provide an update once we have completed our investigation and verified information."

This is the second major violation of the so-called baseline requirements over the past four months. Those requirements were mandated by the CA/Browser Forum, an industry group made up of CAs and the developers of major browsers that trust them. In November, Firefox recommended the blocking of China-based WoSign for 12 months after that CA was caught falsifying the issuance date of certificates to get around a prohibition against use of the weak SHA1 cryptographic hashing algorithm. Other browser makers quickly agreed.

Ayer discovered the unauthorized certificates by analyzing the publicly available certificate transparency log , a project started by Google for auditing the issuance of Chrome-trusted credentials. Normally, Google requires CAs to report only the issuance of so-called extended validation certificates , which offer a higher level of trust because they verify the identity of the holder, rather than just the control of the domain. Following Symantec's previously mentioned 2015 mishap, however, Google required Symantec to log all certificates issued by its CAs . Had Symantec not been required to report all certificates, there's a strong likelihood that the violation never would have come to light.