OID value: 2.16.840.1.113730.1.4
The value is an IA5String. It is a relative or absolute URL that can be used to check the revocation status of any certificates that are signed by the CA that this certificate belongs to. This extension is only valid in CA certificates. The use of this extension is the same as the netscape-revocation-url extension.
URL for further info: http://www.netscape.com/eng/security/cert-exts.html
See also the OID Repository website reference for 2.16.840.1.113730.1.4