New Delhi: Prominent internet browsers Google, Mozilla, Apple and Microsoft have blocked eight digital certificates issued by Indian cybersecurity firm eMudhra Limited after they were found to have critically weak secret keys that could be cracked by anyone to impersonate a website. The security scare sent eMudhra shares plummeting by 20 percent on the National Stock Exchange (NSE) to Rs 432 Wednesday, the lowest price the exchange allowed for the day, known as the lower circuit.
Mozilla, which makes the Firefox browser, has also withdrawn trust in one of eMudhra’s root certificates, and Google will do the same in Chrome.
eMudhra is a Bengaluru-based cybersecurity and digital trust firm that operates as a licensed Certifying Authority (CA). It is the only Indian root certificate authority trusted worldwide. eMudhra issues signature certificates that are used as digital identity cards by individuals and organisations in governance tasks like filing tax returns, provident fund submissions and e-tenders. eMudhra also issues security certificates for websites to make safe connections as well as security solutions for enterprises across the world.
Secrecy is the basis of such digital keys; if they are hacked, fake certificates could be created to impersonate websites, avoid security and intercept traffic.
The flaw was found by an independent security researcher, identified only as ‘Wayne’. According to his account on Mozilla’s public incident tracker, he found the weakness while testing a set of certificate data on the evening of 17 October. At 11.35 pm Indian Standard Time, he emailed Apple, Google, Microsoft, Mozilla and eMudhra with proof, using each of the eight keys to sign a message—something only the holder of a key can do.
What a certificate is, and how weak the keys were
When someone opens a website, the browser checks a digital certificate to confirm that the site is the one it claims to be, and not an imposter. The padlock in the address bar comes from this check.
These certificates are issued by companies called certifying authorities (CAs), which browsers and operating systems agree to trust. The trust works as a chain. At the top is a root certificate, which is kept offline. The root signs intermediate certificates, and the intermediates sign certificates for websites. Each certificate has a private key, a secret number that proves its authority.
If someone obtains an intermediate’s private key, they can issue a certificate for any website, such as a bank’s, and the browser would accept it. Combined with control over a user’s network, for instance on public Wi-Fi, this could be used to impersonate the website or read and alter traffic.
Of the eight affected intermediates, six were for Transport Layer Security (TLS), the system that secures websites. They were held by eMudhra’s companies in the Netherlands and the United States. The other two were for code signing, used to verify that software comes from its stated maker.
The keys use a standard method called elliptic curve cryptography. A private key of this type is meant to be a random number around 115 digits long, so that no computer could guess it. Mozilla engineer Dennis Jackson said all eight eMudhra keys were numbers below 256. Anyone could find them by trying the first 256 possibilities, which takes a fraction of a second. One of the keys was the number 4.
Mozilla said it worked out the keys on its own within about two hours of the report, without knowing the researcher’s method. Jackson said artificial intelligence (AI) tools on a computer also recovered them on the first try from a basic request. Mozilla said the impact of the incident could not be higher, since even people with little technical knowledge could recover the keys.
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How stakeholders reacted
Google said it blocked the six website certificates in Chrome within 1 hour and 40 minutes of the report. It said none of these intermediates had issued website certificates recorded in Certificate Transparency logs, public records that browsers require before trusting a certificate, so no fake certificate could have been trusted by default in Chrome. Google said it checked every other certificate authority in its list and found no other case of this flaw.
Firefox blocked the certificates the same night. Apple and Microsoft followed on October 19 and 20. Sectigo, a United States-based certificate authority that had separately vouched for the same eMudhra certificates, revoked its versions.
On Tuesday, after learning that several people had recovered the keys, some publicly, Mozilla removed eMudhra’’s root, the foundational digital identity certificate it issues and operates, called emSign ECC Root CA – G3, from its trusted list. It said this protects devices that do not receive updates on cancelled certificates. Google said it will do the same, and that some genuine eMudhra customer certificates will stop working as a result. Google said it is also examining whether eMudhra’s remaining root should stay trusted in Chrome, saying certificate authorities must keep showing technical competence. Mozilla said it is not removing that root for now.
On Mozilla’s tracker, eMudhra said the keys were created on 30 April 2025 in a key generation ceremony, a recorded procedure in which keys are produced inside hardware security modules (HSMs), tamper-resistant devices built to hold keys. The keys were meant to be moved to data centres in the United States and Europe for customers needing data stored in those regions. To move them, the company added a step to ‘wrap’ each key, or encrypt it for transfer, and ‘unwrap’ it at the other end. eMudhra said a flaw in the software script created a second, weaker set of keys during this step, and because the two sets had similar names, staff used the weaker ones by mistake. It said human errors occurred at multiple steps.
The company said only one of the eight was put into use, none issued certificates to end customers, and it will re-check every key ceremony it has conducted. It said about 30,000 customer certificates under the removed root must be moved to its other root.
The Computer Emergency Response Team (CERT-In), the government’s cyber security agency under the Ministry of Electronics and Information Technology, issued an advisory on Wednesday on the compromise of eMudhra’s eight intermediate certificates, six used to secure websites and two to sign software. It said the private keys were generated without enough randomness and could be recovered almost instantly, allowing an attacker to issue fake certificates for websites they do not control, impersonate them, and intercept or alter encrypted traffic, which could lead to stolen passwords, leaked data and financial fraud.
The code-signing keys, it said, could be used to make malicious software appear to come from a trusted publisher. CERT-In noted that Mozilla had blocked the certificates and released updated versions of Firefox, and that Google had blocked them in Chrome and will remove eMudhra’s root certificate, emSign ECC Root CA – G3, from its trusted list on 27 October. It also cited Google’s finding that no website certificates from these intermediates appeared in public Certificate Transparency logs before the block, and eMudhra’s statement that none had issued certificates to end users.
The agency warned that removing the root could stop legitimate websites and services from working, and asked government departments, companies, Internet Service Providers and website administrators to update browsers and operating systems, refresh their lists of trusted certificates, find and replace any certificates linked to the affected eMudhra chain, and not bypass certificate warnings.
In its filing to the stock exchanges under rules of the Securities and Exchange Board of India (SEBI), eMudhra said its systems were not breached, no data was lost, and its Indian Digital Signature Certificate (DSC) and eSign services, used for signing tax returns and documents, run on separate systems. It said the affected business is about 1 per cent of revenue, but that harm to its reputation cannot be measured. The company described the matter as “distrust”; Mozilla has classified it as a private key compromise.
Mozilla linked the incident to a 2025 report in which eMudhra published lists of cancelled certificates, called certificate revocation lists, with invalid signatures for the same six intermediates. eMudhra has now said it signed those lists again using the weak keys after the original keys failed.
Updated browsers are protected. Servers running Linux, some Windows computers and applications that carry their own lists of trusted certificates need separate updates.
What comes next
The shares opened at Rs 520 and stayed at Rs 432 with no buyers, having lost Rs 113.25 over five trading days. eMudhra filed its statement at 10.50 am, after trading began.
Mozilla said it is working with eMudhra and others to find the cause. Google’s decision on eMudhra’s remaining root will determine whether the company’s global website certificate business continues in Chrome.
(Edited by Nardeep Singh Dahiya)