Invalid self signed SSL cert - "Subject Alternative Name Missing"

Question

Recently, Chrome has stopped working with my self signed SSL certs, and thinks they're insecure. When I look at the cert in the DevTools | Security tab, I can see that it says

Subject Alternative Name Missing The certificate for this site does not contain a Subject Alternative Name extension containing a domain name or IP address.

Certificate Error There are issues with the site's certificate chain (net::ERR_CERT_COMMON_NAME_INVALID).

How can I fix this?

Answer 1

To fix this, you need to supply an extra parameter to openssl when you're creating the cert, basically

-sha256 -extfile v3.ext

where v3.ext is a file like so, with %%DOMAIN%% replaced with the same name you use as your Common Name. More info here and over here. Note that typically you'd set the Common Name and %%DOMAIN%% to the domain you're trying to generate a cert for. So if it was www.mysupersite.com, then you'd use that for both.

v3.ext

authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
subjectAltName = @alt_names

[alt_names]
DNS.1 = %%DOMAIN%%

Note: Scripts that address this issue, and create fully trusted ssl certs for use in Chrome, Safari and from Java clients can be found here

Another note: If all you're trying to do is stop chrome from throwing errors when viewing a self signed certificate, you can can tell Chrome to ignore all SSL errors for ALL sites by starting it with a special command line option, as detailed here on SuperUser