Intermediate certificates are the links in the chain that let a certificate authority vouch for individual sites.
By late morning, browser makers and some major apps and programming languages had blocked all eight.
Ars Technica reports there are no signs so far that the compromised keys have been used maliciously, based on certificate transparency logs, which publicly record browser-trusted certificates as they are issued.
A standard NIST P-384 elliptic curve key carries roughly 384 bits of entropy, the randomness that makes a key impossible to guess, while the compromised keys ranged from just 3 to 8 bits.
The problem surfaced when an advisory on a site called emudhra.we-have-a-problem.com carried a message signed with one of the keys, proving its holder controlled it.
Ben Cartwright-Cox, director of BGP.tools, guessed that example code may have leaked into production, though he said that is hard to know.
Filippo Valsorda, a cryptography maintainer for the Go programming language, predicted a cleanup larger than Heartbleed, the OpenSSL flaw whose recovery took years, citing a long tail of IoT devices, Docker containers, forgotten Linux machines and tools that ship their own copy of root certificates. eMudhra representatives were not immediately available for comment.
The most immediate risk appears to be for VPN users, particularly in countries whose governments might intercept traffic. End users have little recourse beyond avoiding many non-browser uses of TLS until updates are confirmed. Most browsers have blocked the certificates, but Edge was still connecting to 12 vulnerable hosts when the article was published. Signal, WhatsApp, Wireguard and other apps that don't depend on TLS for confidentiality are not affected. Exploiting the certificates requires an active adversary-in-the-middle attack, in which an attacker sits between two parties and decrypts and re-encrypts their traffic. That is typically within reach of only well-resourced attackers, though anyone controlling a local network, such as at a coffee shop or university, faces a far lower bar.