Mis-issued certificates for 1.1.1.1 DNS service pose a threat to the Internet

The three certificates were issued in May but only came to light Wednesday.

People in Internet security circles are sounding the alarm over the issuance of three TLS certificates for 1.1.1.1, a widely used DNS service from content delivery network Cloudflare and the Asia Pacific Network Information Centre (APNIC) Internet registry.

The certificates, issued in May, can be used to decrypt domain lookup queries encrypted through DNS over HTTPS or DNS over TLS. Both protocols provide end-to-end encryption when end-user devices seek the IP address of a particular domain they want to access. Two of the certificates remained valid at the time this post went live on Ars.

Investigation underway

Although the certificates were issued four months ago, their existence came to public notice only on Wednesday in a post to an online discussion forum. They were issued by Fina RDC 2020, a certificate authority that’s subordinate to the root certificate holder Fina Root CA. The Fina Root CA, in turn, is trusted by the Microsoft Root Certificate Program, which governs which certificates are trusted by the Windows operating system. Microsoft Edge accounts for approximately 5 percent of the browsers actively used on the Internet.

In an emailed statement sent several hours after this post went live, Cloudflare officials confirmed the certificates were improperly issued. They wrote in part:

Cloudflare did not authorize Fina to issue these certificates. Upon seeing the report on the certificate-transparency email list, we immediately kicked off an investigation and reached out to Fina, Microsoft, and Fina’s TSP supervisory body – who can mitigate the issue by revoking trust in Fina or the mis-issued certificates. At this time, we have not yet heard back from Fina.

The statement went on to say that data encrypted through Cloudflare's WARP VPN isn't affected.

Microsoft said in an email that it has “engaged the certificate authority to request immediate action. We’re also taking steps to block the affected certificates through our disallowed list to help keep customers protected.” The statement didn't say how the company failed to identify the improperly issued certificate for such a long period of time.

Representatives from Google and Mozilla said in emails that their Chrome and Firefox browsers have never trusted the certificates, and there was no need for users to take any action. An Apple representative responded to an email with this link to a list of certificate authorities Safari trusts. Fina was not included.

It wasn't immediately known which organization or person requested and obtained the credentials. Representatives from Fina, didn’t answer emails seeking details.

The certificates are a key part of the Transport Layer Security protocol. They bind a specific domain to a public key. The certificate authority, the entity authorized to issue browser-trusted certificates, possesses the private key certifying that the certificate is valid. Anyone in possession of a TLS certificate can cryptographically impersonate the domain for which it was issued.

The holder of the 1.1.1.1 certificates could potentially use them in active adversary-in-the-middle attacks that intercept communications passing between end users and the Cloudflare DNS service, Ryan Hurst, CEO of Peculiar Ventures and a TLS and public key infrastructure expert, told Ars.

From there, attackers with possession of the 1.1.1.1 certificates could decrypt, view, and tamper with traffic from the Cloudflare DNS service, Hurst said.

Castles made of sand

Wednesday’s discovery exposes a key weakness of the public key infrastructure that’s responsible for ensuring trust of the entire Internet. Despite being the only thing ensuring that gmail.com, bankofamerica.com or any other website is controlled by the entity claiming ownership, the entire system can collapse with a single point of failure.

Cloudflare's statement observed:

The CA ecosystem is a castle with many doors: the failure of one CA can cause the security of the whole castle to be compromised. CA misbehavior, whether intentional or not, poses a persistent and significant concern for Cloudflare. From the start, Cloudflare has helped develop and run Certificate Transparency that has allowed this mis-issuance to come to light.

The incident also reflects poorly on Microsoft for failing to proactively catch the mis-issued certificates and allowing Windows to trust them for such a long period of time. Certificate Transparency, a site that catalogues in real time the issuance of all browser-trusted certificates, can be searched automatically. The entire purpose of the logs is so stakeholders can quickly identify mis-issued certificates before they can be actively used. The mis-issuance in this case is easy to spot because the IP addresses used to confirm the party applying for the certificates had control of the domain was 1.1.1.1 itself.

The public discovery of the certificates four months after the fact suggests the transparency logs didn’t receive the attention they were intended to get. It's unclear how so many different parties could miss the certificates for such a long time span.

This story was updated to correct an explanation of TLS certificates and to report newly available details.

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Posted Thursday 4 September 2025 at 2:59 pm AEST (my time).

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