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. Users of Apache CXF 3.4.x should update to 3.4.3; Users of Apache CXF 3.3.x should update to 3.3.10; Users of any other versions of CXF should upgrade to one of these supported releases. Reference: http://cxf.apache.org/security-advisories.data/CVE-2021-22696.txt.asc
