[Apache CXF] CVE-2021-22696: OAuth 2 authorization service vulnerable to DDos attacks

[Colm O hEigeartaigh <co...@apache.org>]

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