Sure, but a client that doesn't do CT wouldn't care if they don't include a SCT promise. [ed.: this said "break the SCT promise", that doesn't quite make sense] Which you'd only notice if you see the certificate somewhere else afterwards…

It's all rather hypothetical and unlikely, but you could certainly try attacking something like downloads.openwrt.org¹ like that — especially if you can tell apart the TLS client in opkg from a normal browser.

(¹ luckily, OpenWRT and most other package repos don't actually rely on HTTPS for package integrity and authenticity. And OpenWRT would be the most susceptible due to the "exotic" TLS client stack, if any.)

I’m surprised to see this username above this comment.

No, the cert can be issued with no (or invalid/junk) SCT and will work fine with clients who don’t check SCT, which is most non-browser interaction.

Every cert an attacker issues with eMudhra's private key has to appear in the CT logs if they want it to validate in a modern browser.

But if you only want to MITM the connection used by 'pip' to install python wheels - that doesn't check for CT records at all.

No, it doesn't. A certificate may or may not include CT info, or include fake CT info. Most TLS clients accept certificates without checking for CT.

SCT enforcement falls to the client though, yeah? What's stopping someone from signing a rogue cert silently which is accepted by CT-lenient clients?