Leaked Keys Enable Domain Impersonation

Eight private keys tied to intermediate certificate authority credentials have been leaked, creating a security gap that allows attackers to impersonate any domain. This issue affects the security infrastructure used to verify the identity of websites and software, potentially enabling malicious actors to intercept connections on networks such as corporate systems, public Wi-Fi, or internet service providers.

With these compromised credentials, an attacker positioned in the path of network traffic can pretend to be a trusted entity like apple.com, amazon.com, or bankofamerica.com. Because the associated code-signing certificates are also affected, a downloaded application could be presented as legitimate software from major vendors like Microsoft or Google. If an operating system or application has not been updated to reject these keys, it would fail to detect the deception.

Software typically verifies a certificate by checking its chain of trust. A website’s certificate is issued by an intermediate Certification Authority (CA), which is in turn signed by root certificates whose private keys are kept offline. In this instance, the Indian CA firm eMudhra issued six TLS and two code-signing intermediate certificates using private keys that were extremely short, specifically only one byte long. This means the secret key was a number between 0 and 255, making it trivial to guess.

Operating systems and applications maintain lists of trusted root certificates and CAs. Browsers also maintain lists of certificates that must not be trusted, known as revocation lists. To resolve this issue, these lists must be updated to revoke the eight affected CAs, remove the affected root certificate, or explicitly reject the eight compromised keys.

There is a safeguard for users who browse the web using recent versions of Chrome, Brave, Firefox, and Safari. These browsers enforce a feature called Certificate Transparency, which consults a public log of issued certificates and blocks any that are not recorded there. According to reports, no certificates signed by the affected intermediate CAs were logged, suggesting that regular web browsing is safe for users of these updated browsers.

However, the scope of the required updates is extensive. The vulnerability impacts a wide array of systems, including PCs, servers, operating systems, phones, tablets, routers, and virtual machines. It also extends to development tools and languages such as Python, Go, Node.js, Rust, and utilities like curl. While updates are expected for actively maintained software, older devices like smart appliances and outdated routers could present a problem.

The cause of the extremely short private keys remains under investigation. Administrators and users are advised to update all software and devices immediately to protect against this impersonation risk.