Why Is My Wildcard SSL Not Working on a Second Level Subdomain?

An In-Depth Look at Why a Wildcard SSL Certificate Causes a Domain Mismatch Error on a Second Level Subdomain

We know, you’re here because your wildcard SSL is not working on a second level subdomain for some reason. To help you understand why, we first need to tell you a bit about wildcard SSL certificates and what they do and don’t secure. The digital certificate industry is, at times, needlessly opaque about what its products actually do. The wildcard is one of the biggest offenders. It’s often marketed as securing “unlimited subdomains.” And that’s partially true — with one important caveat:

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Error Code SEC_ERROR_UNKNOWN_ISSUER — How to Fix it in Firefox

Troubleshooting a common SSL certificate error

One of the more frustrating aspects of web browsers and the errors they generate is that they all generally use different nomenclature. While Chrome and Opera tend to operate on the same plane, Safari, Firefox and Microsoft Edge all do their own thing. Case in point, let’s consider the error code SEC_ERROR_UNKNOWN_ISSUER in Firefox.

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