CVE-2026-14440
MediumCVSS 6.8Exploitation Probability (EPSS)
Low risk3th percentile — higher than 3% of all known CVEs
Summary
A vulnerability in Cloudflare Universal SSL allows bypassing strict CAA records with accounturi or validationmethods parameters (RFC 8657) during TLS certificate issuance. The auto-managed CAA RRset overrides customer configuration, potentially enabling an attacker to obtain a trusted certificate for the victim's domain.
Risk Assessment
The risk involves a potential MITM (man-in-the-middle) attack on a Cloudflare customer's domain if an attacker can obtain a TLS certificate from a trusted CA. Exploitation requires additional conditions, such as holding an ACME account and bypassing multi-perspective validation.
Recommendation
Disable Universal SSL on zones requiring strict enforcement of CAA records with RFC 8657 parameters. Additionally, implement Certificate Transparency (CT) monitoring to detect unauthorized certificate issuance.
Original NVD description (English source)
Description: To issue and renew TLS certificates on behalf of customers, Cloudflare's Universal SSL feature automatically manages the CAA RRset for the customer's zone. This auto-managed RRset is permissive by design (e.g. 'issue "letsencrypt.org"' without parameters). On Universal SSL zones, Cloudflare's authoritative DNS serves this auto-managed RRset at query time, superseding any customer-configured CAA records on the zone. When a customer publishes a stricter CAA record using the RFC 8657 accounturi or validationmethods parameters, the Certificate Authority does not observe those parameters when evaluating the served RRset under RFC 8659. As a result, the RFC 8657 account-binding and validation-method-binding protections are not enforced end-to-end on Universal SSL zones. Successful exploitation could result in issuance of a browser-trusted TLS certificate to an attacker, enabling MITM against the affected domain. Exploitation is non-trivial in practice: an attacker would need to hold an ACME account at one of the Certificate Authorities in the served CAA RRset and to simultaneously satisfy domain control validation across the multiple geographically distinct Network Perspectives the CA relies on for Multi-Perspective Issuance Corroboration. Cloudflare prefixes are anycast-announced from hundreds of locations globally, raising the bar against single-vantage-point BGP hijacks. Any resulting misissuance of a browser-trusted certificate is subject to Certificate Transparency logging required by major browsers, and would be visible to CT monitoring. Mitigation: Customers requiring strict RFC 8657 enforcement need to disable Universal SSL on the affected zone. Universal SSL's automatic CAA management and customer-set RFC 8657 accounturi and validationmethods enforcement are mutually exclusive by the nature of the issue, so there is no in-product workaround that preserves both. Certificate Transparency monitoring is recommended for all customers as a general detection control. Credits: David Osipov (ORCID: https://orcid.org/0009-0005-2713-9242), independent researcher