CXF supports (via JwtRequestCodeFilter) passing OAuth 2 parameters via a JWT token as opposed to query parameters (see: The OAuth 2.0 Authorization Framework: JWT Secured Authorization Request (JAR)). Instead of sending a JWT token as a "request" parameter, the spec also supports specifying a URI from which to retrieve a JWT token from via the "request_uri" parameter. CXF was not validating the "request_uri" parameter (apart from ensuring it uses "https) and was making a REST request to the parameter in the request to retrieve a token. This means that CXF was vulnerable to DDos attacks on the authorization server, as specified in section 10.4.1 of the spec. This issue affects Apache CXF versions prior to 3.4.3; Apache CXF versions prior to 3.3.10.
We recommend upgrading to a version of this component that is not vulnerable to this specific issue.
Note: If this component is included as a bundled/transitive dependency of another component, there may not be an upgrade path. In this instance, we recommend contacting the maintainers who included the vulnerable package. Alternatively, we recommend investigating alternative components or a potential mitigating control.