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There's two Let's Encrypt issues at play at the moment. The issue that your comment about cached/discovered intermediates relates to is that some servers were

There's two Let's Encrypt issues at play at the moment. The issue that your comment about cached/discovered intermediates relates to is that some servers were still manually constructing the chain that goes leaf -> R3 -> DST Root X3, and the R3 intermediate signed by X3 expired on 29 September. This chain hasn't been returned by Let's Encrypt since May 2021. The other issue relates to the current default chain returned by Let's Encrypt that goes leaf -> R3 -> ISRG Root X1 -> DST Root X3 for Android compatibility. Most clients are able to successfully build a valid chain from the leaf to the still valid ISRG X1, however, old versions of OpenSSL (pre-1.1.0) and several other TLS libraries that don't explore the graph correctly barfs at a chain that terminates in the now expired X3 root. [1]: https://community.letsencrypt.org/t/production-chain-changes/150739 https://community.letsencrypt.org/t/production-chain-changes...

tialaramex 5y ago
Well, you're right that there are two issues, and it's perhaps unfortunate that ISRG chose to arrange that they happen next to each other (but to be fair I don't think we pressed them to do anything else back when it would have been possible, although I'm behind on some reading I don't think I'm that far behind) But, in both cases Firefox's choice works out for it regardless. And unfortunately I believe -- though it's hard to tell for sure -- that some other browsers get the missing certificate case wrong, perhaps for a few hours and perhaps much longer. Lacking a guiding hand, they may end up choosing to "validate" the R3 -> DST Root CA X3 case which can't work. I think some logic will eventually expire this useless data and those browsers will work, but obviously that's not helpful if your site seems "broken" now. It will be clearer by tomorrow, but understandably Let's Encrypt's community site is under a deluge of "Help!?" type posts, which are a struggle for the volunteers.

tialaramex 5y ago

Well, you're right that there are two issues, and it's perhaps unfortunate that ISRG chose to arrange that they happen next to each other (but to be fair I don't think we pressed them to do anything else back when it would have been possible, although I'm behind on some reading I don't think I'm that far behind) But, in both cases Firefox's choice works out for it regardless. And unfortunately I believe -- though it's hard to tell for sure -- that some other browsers get the missing certificate case wrong, perhaps for a few hours and perhaps much longer. Lacking a guiding hand, they may end up choosing to "validate" the R3 -> DST Root CA X3 case which can't work. I think some logic will eventually expire this useless data and those browsers will work, but obviously that's not helpful if your site seems "broken" now. It will be clearer by tomorrow, but understandably Let's Encrypt's community site is under a deluge of "Help!?" type posts, which are a struggle for the volunteers.