Universal SSL: Protection Mechanism Failure
CVE-2026-14440 is a high-severity protection mechanism failure vulnerability in Universal SSL from Cloudflare, with a CVSS 4.0 base score of 7.6 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected Universal SSL versions: current and earlier. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.3% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Universal SSL you run against the affected versions below, and install the vendor's latest release.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cloudflare | Universal SSL | current and earlier | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- AdjacentThe attacker must be on the same local network segment.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Attack requirements
- PresentThe target must be in a specific state or configuration for the attack to work.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- HighSerious loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- NoneNo loss of availability on the vulnerable system.
- Confidentiality (other systems)
- NoneNo loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- NoneNo loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- NoneNo loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:A/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (cloudflare.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.6 | High | CNA (cloudflare.com) |
| CVSS 3.1 | 6.8 | Medium | CISA (ADP) |
Official description
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
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Protection Mechanism Failure
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
- developers.cloudflare.com/ssl/edge-certificates/caa-records/
- developers.cloudflare.com/ssl/edge-certificates/universal-ssl/limitations/
- rfc-editor.org/rfc/rfc8657
- rfc-editor.org/rfc/rfc8659
- community.cloudflare.com/t/critical-security-gap-cloudflare-must-fully-support-rfc-8657-caa/799999/10
- community.cloudflare.com/t/universal-ssl-exposes-domains-to-bgp-leaks-re-venezuela-analysis/879930
- david-osipov.vision/en/blog/cybersecurity/cloudflare-ssl-mitm-flaw-2026/
- zenodo.org/records/18330221
Recent Protection Mechanism Failure vulnerabilities
- 7.5 High severity
- 9.6 Critical severity
- 9.6 Critical severity
- 9.6 Critical severity
- 8.3 High severity
- 9.6 Critical severity
Spotted an error? Tell us.