A test website is available at <https://emudhra.we-have-a-problem.com/> which also lists mitigation options for systems which do not receive CRL or equivalent revocation updates. Effectively: disable the root CAs "emSign ECC Root CA - G3" and "Comodo AAA Services root" in your operating system trust store, while being mindful of collateral damage. The Comodo root in particular has been widely used in the past.
The site also has a zip file with signatures using the private keys of the affected intermediate certificates, which verify using OpenSSL. Postings on social media claim that the private keys are easily discoverable. -valtteri
