eMudhra's CA private keys were literally the number 4
Eight Bits of Trust; eMudhra's CA keys cracked in milliseconds
Eight eMudhra intermediate CA private keys turned out to be single-byte numbers — 4, 56, 115, and so on — that anyone could brute-force in milliseconds from the public certificates. The keys date to April 2025, and the flaw can't be contained: browsers blocked the intermediates within days, but curl, Python, Node, Go, Java, and frozen IoT firmware still trust them. Scott Helme forged a certificate for api.stripe.com and watched default clients accept it.
They are inherently weak single-byte keys that anyone can factor, and the issue cannot be contained.