Mozilla has asked all certificate authorities (CAs) to revoke subordinate CA certificates currently used for corporate SSL traffic management, offering an amnesty to any CAs that had breached Mozilla's conditions for having their root certificates ship with its products.
The request comes after Trustwave recently admitted to issuing a sub-CA certificate to a private company for use in a data loss prevention system. Sub-CA keys can be used to sign SSL certificates for any domain name on the Internet, which makes them very dangerous if they fall in the wrong hands.
Even though Trustwave argued that the sub-CA key in question was stored in a hardware security module (HSM), making it irretrievable, the fact that such a powerful certificate was issued to a private company that wasn't a certificate authority represents a violation of Mozilla's policy.
Certificate authorities voluntarily adhere to Mozilla's CA Certificate Policy in order to have their root keys included by default in Firefox, Thunderbird and other Mozilla products.
"Participation in Mozilla's root programme is at our sole discretion, and we will take whatever steps are necessary to keep our users safe, up to and including the removal of root certificates that mis-issue, as well as any roots that cross-sign them," said Johnathan Nightingale, senior director of Firefox Engineering at Mozillay.
Because there is reason to believe that multiple CAs engage in this type of behaviour, Mozilla has decided to offer everyone a one time chance to come clean about it without risking repercussions instead of making an example out of Trustwave, which would likely discourage similar disclosures.
"We believe that security is best served when browsers and CAs can work together; we hope that frank communication and clear expectations can resolve these issues before any such action is required," Nightingale said.
Mozilla made its amnesty offer in an email to all CAs, asking them to revoke sub-CA certificates used for SSL man-in-the-middle interception or traffic management and to destroy the corresponding HSMs.
"We have requested the serial numbers of those certificates and fingerprints of their signing roots so that we, and other relying parties, can detect and distrust these subCA certificates if encountered," Nightingale said.
CAs have until April 27 to comply with these requests. If such certificates are found after that date, the issuing CAs will face punishments including the removal of their root keys from Mozilla's products. In theory, such forced removals could put those CAs out of business because all the certificates they ever signed would no longer work properly. However, this would only be 100 percent effective if all browser and operating system vendors agree to do it.
It remains to be seen how CAs will respond to Mozilla's requests, especially since they probably have contractual obligations to customers who bought such sub-CA certificates. Experts previously said that two months will not be enough for companies to replace SSL traffic inspection systems that currently use sub-CA certificates with something else.