Edit: source https://groups.google.com/forum/#!topic/mozilla.dev.security...
Incident 2 ----------
In July 2016, it became clear that there was some problems with the StartEncrypt automatic issuance service recently deployed by the CA StartCom. As well as other problems it had, which are outside the scope of this discussion, changing a simple API parameter in the POST request on the submission page changed the root certificate to which the resulting certificate chained up. The value "2" made a certificate signed by "StartCom Class 1 DV Server CA", "1" selected "WoSign CA Free SSL Certificate G2" and "0" selected "CA 沃通根证书", another root certificate owned by WoSign and trusted by Firefox.
Using the value "1" led to a certificate which had a notBefore date (usage start date) of 20th December 2015, and which was signed using the SHA-1 checksum algorithm.
* The issuance of certificates using SHA-1 has been banned by the Baseline Requirements since January 1st, 2016. Browsers, including Firefox, planned to enforce this[2] by not trusting certs with a notBefore date after that date, but in the case of Firefox the fix had to be backed out due to web compatibility issues. However, we are considering how/when to reintroduce it, and CAs presumably know this.
* The issuance of backdated certificates is not forbidden, but is listed in Mozilla's list of Problematic Practices[3]. It says "Minor tweaking for technical compatibility reasons is accepted, but backdating certificates in order to avoid some deadline or code-enforced restriction is not."
* WoSign deny that their code backdated the certificates in order to avoid browser-based restrictions - they say "this date is the day we stop to use this code"[4]. If that is true, it is not clear to us how StartCom came to deploy WoSign code that WoSign itself had abandoned.
* It seems clear from publicly available information that StartCom's issuance systems are linked to WoSign's issuance systems in some way. Nevertheless, it should not have been possible for an application for a cert from StartCom to produce a cert signed by WoSign.
* This misissuance incident was not reported to Mozilla by WoSign as it should have been.