PKI Threats

Cert Spotter mitigates the security flaws in the Web's Public Key Infrastructure.

The certificate authority system suffers from the "lowest common denominator" problem: there are hundreds of certificate authorities that are trusted to sign certificates for any website on the Internet. This means that the security of every website on the Internet depends on the security of the least secure certificate authority. Although some CAs pride themselves on their higher validation standards and trustworthiness, choosing such a CA does a website operator little good. Even if you do business with a top-tier CA, an attacker can exploit a less rigorous CA to get a valid certificate for your domain. Since web browsers treat certificates from all CAs the same, visitors to your site won't notice a difference unless they look at advanced dialogs, which few do.

The domain validation risk

Domain validated (DV) certificates present additional security challenges, since validation and issuance are often entirely automated. This creates a risk of vulnerabilities in the API which allow attackers to trick the CA into issuing certificates for domains they don't control. Early versions of the automated APIs used by StartCom and Let's Encrypt suffered from such flaws.

Since out-of-band confirmation is not required to obtain a domain validated certificate, a temporary compromise can lead to a long-term fraudulent certificate. Once an attacker has control over a domain's DNS, web server, or email provider, they can obtain a certificate for the domain that remains valid long after the compromise is detected, and can use it to attack the domain even after the compromise is remediated.

CAs validate domain ownership over insecure channels, such as unauthenticated DNS, insecure HTTP, and email. These channels are susceptible to man-in-the-middle and man-on-the-side attacks from BGP hijacking or compromised routers. A powerful attacker who compromises the validation channel can obtain unauthorized certificates for domains. Unfortunately, requiring a secure channel to obtain a certificate would create a chicken-and-egg problem, since securing the channel would itself require a certificate.

The solution: Certificate Transparency

Despite the security challenges posed by DV, the answer is not to make it harder to obtain certificates. Easy-to-obtain certificates are essential for moving the Web to HTTPS. Nor are the problems with the certificate authority system reason to abandon the system and replace it with something new and untried. Instead, the answer is Certificate Transparency. Certificate Transparency helps domain owners detect unauthorized certificates for their domains and take corrective action, such as contacting the CA to have the certificate revoked. Certificate Transparency also reduces the likelihood of unauthorized certificates in the first place, since CAs are incentivized to improve their security, and attackers are discouraged from attempting attacks that will be detected.

Certificate Transparency only works if domain owners are watching. Cert Spotter monitors Certificate Transparency logs and alerts you when a certificate is issued for one of your domains. If the certificate is unauthorized, you can stop the attack and protect your data and reputation. Cert Spotter is the tool you need to protect yourself from the threats in the Web's public key infrastructure.

Learn more about Certificate Transparency

See a timeline of certificate authority security failures

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