WHO DO YOU TRUST WHEN YOU TRUST A CERTIFICATE? THE EMUDHRA INCIDENT EXPLAINED

Summary from the TLDR InfoSec newsletter

One of eight compromised eMudhra intermediate CA private keys was literally the number 4, the result of a flawed April 2025 key ceremony that left the top 376 bits of every key zeroed. Browsers blocked the intermediates within hours through OneCRL, CRLSets, and Certificate Transparency checks, but Python, Go, Node, Java, and curl skipped revocation entirely and kept trusting forged chains until their bundled trust stores changed. The fixes split along architecture lines, with certifi, Debian, and uv dropping the entire emSign G3 root while Go and Node denylisted only the eight broken keys, sparing roughly 30,000 legitimate certificates.