Anyone could compute the keys of eight eMudhra intermediate certificates, so tools outside browsers need updates
The private keys of eight intermediate certificates from the certificate authority eMudhra were small numbers that anyone could compute. Firefox, Chrome, Apple, and Microsoft blocked the certificates within three days, and Mozilla and Chrome are now removing trust in the root above them. Software with its own copy of the certificate list, from Python's certifi to Go, needs an update.
Source
Private key compromise of eMudhra Intermediate CertificatesMozilla Bugzilla · Original published October 20, 2026
Eight intermediate certificates issued by the certificate authority eMudhra had private keys that could be computed almost instantly, Mozilla confirmed after a report on October 17, 2026. Anyone holding such a key could issue a certificate that impersonates any website. Browsers already reject the certificates. Programs that keep their own list of trusted certificates, and servers with outdated system packages, need an update.
What was wrong with the keys
An intermediate certificate is the one a certificate authority uses to sign website certificates. A root certificate signs it in turn, and browsers and operating systems trust that root directly. Whoever controls an intermediate's private key can therefore issue certificates that clients will accept.
A P-384 private key is supposed to be a random number up to 384 bits long. Dennis Jackson of Mozilla wrote in the incident report that each of the eight keys was an integer smaller than 256. A key like that turns up almost immediately by trying the first 256 candidates.
The eight keys came from a single key ceremony in 2025. Six belong to certificates for encrypted web connections (TLS) and chain to roots trusted by Chrome, Mozilla, Microsoft, and Apple. The other two are for code signing and are trusted by Microsoft. Jackson also wrote that local AI agents recovered a key on the first attempt from a simple prompt.
What browsers and the certificate authority did
A researcher who signs as Wayne sent the root programs and eMudhra proof of control over all eight keys on October 17, 2026. Mozilla recovered the keys independently the same evening. According to the incident site, Firefox and Chrome have blocked the certificates since October 17, Apple devices since October 19, and Microsoft platforms since October 20.
eMudhra revoked the eight certificates on October 18. Sectigo, which had cross-signed some of them, revoked its versions on October 19. On October 20, 2026, Mozilla announced the emergency removal of trust in the root certificate emSign ECC Root CA - G3, because several people had recovered the keys independently and at least one had published them. Chrome said it would take a similar path.
eMudhra says it stopped issuing certificates under that root on October 20. The company estimates that about 30,000 certificates must move to intermediates under its RSA root, emSign Root CA - G1. It says about 97% of them were issued through ACME, the protocol for automated certificate issuance, and that the compromised intermediates never issued a certificate to an end user.
Who still needs to update
Browsers check Certificate Transparency, public logs in which every certificate they trust must appear. According to the incident site, those logs show no certificates from these intermediates, so Firefox, Chrome, Edge, and Safari could not have been attacked. Many clients outside browsers do not check the logs, and it is not known whether anyone exploited the flaw against them.
Those clients include programs that carry their own copy of the trusted certificate list instead of using the operating system's. The incident site lists these fixed versions, among others:
- Python: certifi 2026.10.19, pip 26.2.2, and uv 0.13.4
- Go 1.27.3 and 1.26.10
- Electron 44.9.1
- the curl CA bundle dated 2026-10-20
- the
ca-certificatespackages of Ubuntu, Debian, Alpine, Arch Linux, and Fedora
For Node.js and Bun, the table still marked the fix as pending on October 21, 2026. The site also warns that the curl built into macOS checks certificates against a file that has not been updated and does not check revocation, even though macOS itself blocks the certificates.
„the impact of this incident could not be higher“
Sources
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