eMudhra (emSign) certificate authority compromise: fixed

What happened

eMudhra runs emSign, a certificate authority whose certificates prove that a website is who it says it is. In April 2025 it created eight intermediate certificate authorities, six for website certificates and two for code signing, whose private keys were not random: they were so small that anyone can work them out from the public certificates in under a second. eMudhra attributes this to an error in its key-generation ceremony.

The weakness was reported to the browser root programs on October 17, 2026. Chrome and Firefox blocked the eight authorities that day, eMudhra revoked them on October 18, Apple and Microsoft blocked them on October 19 and 20, and Mozilla removed the emSign root they chain to. Anyone can recover the keys and use them to issue a certificate for any website, which software that still trusts these authorities will accept.

Each authority also exists as a copy cross-signed by another certificate authority, Sectigo, with the same key. Distrusting the emSign root alone therefore does not stop every path to them.

How it affected OhrTech devices

Android trusted the emSign root, and it does not check whether a certificate has been revoked. Revocation alone therefore does not protect Android devices. We confirmed on OhrTech hardware that, before the fix, Android's built-in WebView, which apps use to show web pages, accepted a test site using a certificate from one of the compromised authorities.

Anyone with a position on the network path, such as a hostile Wi-Fi network or a compromised router, could have impersonated any HTTPS site to apps that use Android's standard secure connections or its WebView and do not pin certificates. Customer apps are among them.

We know of no use of the keys against OhrTech devices. Before browsers blocked them, no website certificates from these authorities had appeared in the public certificate logs.

Device management was not affected. The OhrTech Agent's connection to the OhrTech Portal does not rely on certificate authorities: its server key is pinned, and its messages are signed and end-to-end encrypted. A forged certificate cannot read or alter them.

What we did

We released the fix on October 21, 2026, the day after the compromise was disclosed. Foundation OS release 2026101906:

• removes emSign ECC Root CA - G3, the root Mozilla removed, from both of Android's certificate stores, together with the two older emSign roots Mozilla is retiring;
• adds Chromium's list of compromised keys to Android's secure-connection library, so the eight authorities are refused whichever certificate they arrive in, including Sectigo's cross-signed copies.

We tested it on our devices: sites using the compromised authorities are refused, by apps and by Android's built-in WebView, and other sites connect normally.

We have also put new measures in place so that we can respond to incidents like this one even faster. Our servers now block compromised certificate authority keys on devices within hours of their being blocked elsewhere, and keep the list of trusted certificate authorities current by following Mozilla's, without waiting for a system update.

Who needs to act

• Apps that use Android's built-in networking or its built-in WebView are protected. They need no change.
• Apps that bring their own certificate list or TLS library, such as a custom trust store, a bundled BoringSSL or OpenSSL, Flutter, Go or Rust networking, or a third-party web browser with its own root list, do not use Android's protections. Update them to versions that block these authorities (for Go, 1.27.3 or 1.26.10), or remove eMudhra from their trust data. Do not work around errors by turning off certificate checks.
• If your servers use eMudhra or emSign certificates, replace them with certificates from another certificate authority. OhrTech devices now refuse them.

Credit

The weakness was reported to the browser root programs by a researcher who signs as Wayne. Mozilla's incident report and the public disclosure are linked under References.