An Egyptian company that created unauthorized digital certificates for several Google domains said Wednesday it made a mistake and acted quickly when the error became known.
The SSL/TLS (Secure Sockets Layers/Transport Layer Security) certificates would have allowed MCS Holdings of Cairo to decrypt traffic sent by users on its network to Google, a major privacy concern. Google said it doesn’t believe the certificates were misused.
But MCS shouldn’t have been able to create digital certificates for Google properties in the first place. It appears MCS and a Certificate Authority (CA) in China both made mistakes, which highlight ongoing problems in the way digital certificates are issued.
MCS obtained an intermediate certificate from the China Internet Network Information Center (CNNIC), a CA, for a cloud-based service it planned to launch, the company said in a statement Wednesday. It received the certificate on March 19 and it was valid for two weeks while it tested its new service.
But CNNIC had issued a certificate that was too powerful and allowed MCS to generate certificates for any domain, not just the ones it operates. It essentially made MCS Holdings a sub-Certificate Authority.
Certificate Authorities are bound by requirements from browser makers to ensure the security of the certificate system. That’s because browsers are coded to trust vetted CAs, and the browsers will not generate a warning if a website carries a certificate from a known, trusted party.
Mozilla, for example, requires that intermediate digital certificates must be publicly disclosed or subject to audits, or else technically constrained to prevent them from being abused.
Discussions are underway on whether CNNIC should be removed from the CAs trusted by Mozilla, or if the organization’s certificates should be limited to .cn domains only.
CNNIC’s mistake was magnified by MCS Holdings. The company put the intermediate certificate in a firewall that was FIPS compliant in order to protect its private key.
The firewall, however, was configured as an SSL forward proxy. Those type of man-in-the-middle proxies will terminate an SSL connection so encrypted traffic can be inspected, a security measure performed by some organizations.
To do that traffic inspection, companies usually generate their own self-signed CA certificates. But the firewall at MCS used its intermediate certificate, which gave it the great power to generate ones for Google.
Google, which uses a technique called certificate key pinning to detect unauthorized certificates, discovered the problem March 20 and notified CNNIC, according to a blog post Monday. MCS said in its statement that it deleted the certificates after it was notified by CNNIC.
MCS Holdings said the incident was a “human mistake” that occurred in its lab when one of its employees was browsing the Internet using Google’s Chrome browser. Microsoft, Google and Mozilla have all taken steps to block the rogue certificates.