A security researcher reported that the private keys for eight eMudhra intermediate certificates were compromised. Chrome pushed a CRLSet update blocking them on Saturday, 17 October, and Mozilla blocked them in Firefox via OneCRL a few hours later. On Tuesday, 20 October, Mozilla announced the issue publicly and shipped an NSS update removing the eMudhra root, and Chrome confirmed the root is going in Chrome Root Store v43.
The eight intermediates are six TLS issuing CAs (DV, OV and EV, two generations each) and two code-signing CAs, all created in April 2025. Each was also cross-signed by Sectigo's AAA Certificate Services root in May 2025.
The flaw lies in the keys themselves. The private keys are elliptic-curve keys on the P-384 curve, where the private key should be a random 384-bit number. Instead, the keys are tiny: one eMudhra key is simply 4, another is 56, another is 115. The researcher recovered all 16 affected certificates on a laptop in under a second by checking each possible value, because a single byte has only 256 possibilities.
Nothing about the certificates looked wrong, since each public key derived from a small number is still a valid point on the curve. Because the keys were effectively public from the day the certificates were issued, anyone could have recovered them since April 2025, and there is no way to know whether someone did.
Source: Hacker News · Summarized by HeadlinesBriefing