CVE-2021-21378 (C++, published 2021-03-11T03:15Z)
Description: value: Envoy is a cloud-native high-performance edge/middle/service proxy. In Envoy version 1.17.0 an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list when Envoy's JWT Authentication filter is configured with the `allow_missing` requirement under `requires_any` due to a mistake in implementation. Envoy's JWT Authentication filter can be configured with the `allow_missing` requirement that will be satisfied if JWT is missing (JwtMissed error) and fail if JWT is presented or invalid. Due to a mistake in implementation, a JwtUnknownIssuer error was mistakenly converted to JwtMissed when `requires_any` was configured. So if `allow_missing` was configured under `requires_any`, an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list. Integrity may be impacted depending on configuration if the JWT token is used to protect against writes or modifications. This regression was introduced on 2020/11/12 in PR 13839 which fixed handling `allow_missing` under RequiresAny in a JwtRequirement (see issue 13458). The AnyVerifier aggregates the children verifiers' results into a final status where JwtMissing is the default error. However, a JwtUnknownIssuer was mistakenly treated the same as a JwtMissing error and the resulting final aggregation was the default JwtMissing. As a result, `allow_missing` would allow a JWT token with an unknown issuer status. This is fixed in version 1.17.1 by PR 15194. The fix works by preferring JwtUnknownIssuer over a JwtMissing error, fixing the accidental conversion and bypass with `allow_missing`. A user could detect whether a bypass occurred if they have Envoy logs enabled with debug verbosity. Users can enable component level debug logs for JWT. The JWT filter logs will indicate that there is a request with a JWT token and a failure that the JWT token is missing.
Severity: MEDIUM (CVSS v3 base score: 8.2)
Weakness: CWE-287 \u2014 Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
Repository: https://github.com/envoyproxy/envoy
Files changed:
docs/root/version_history/current.rst
source/extensions/filters/http/jwt_authn/verifier.cc
test/extensions/filters/http/jwt_authn/all_verifier_test.cc
test/extensions/filters/http/jwt_authn/group_verifier_test.cc
Commit message: jwt_authn: fix a bug where JWT with wrong issuer is allowed in allow_missing case (#15194)

[jwt] When allow_missing is used inside RequiresAny, the requests with JWT with wrong issuer are accepted. This is a bug, allow_missing should only allow requests without any JWT. This change fixed the above issue by preserving JwtUnknownIssuer in allow_missing case.

Signed-off-by: Wayne Zhang <qiwzhang@google.com>

Vulnerable code:
      // JwtMissing should be treated differently than other failure status
      // since it simply means there is not Jwt token for the required provider.
      // If there is a failure status other than JwtMissing in the children,
      // it should be used as the final status.
        // If a Jwt is extracted from a location not specified by the required provider,
        // the authenticator returns JwtUnknownIssuer. It should be treated the same as
        // JwtMissed.
        if (child_status != Status::JwtMissed && child_status != Status::JwtUnknownIssuer) {
  EXPECT_CALL(mock_cb_, onComplete(Status::Ok));
  EXPECT_CALL(mock_cb_, onComplete(Status::Ok));
// Test RequiresAny with two providers and allow_missing, but OK
TEST_F(GroupVerifierTest, TestRequiresAnyWithAllowMissingButOk) {
  EXPECT_CALL(mock_cb_, onComplete(Status::Ok));

Fixed code:
* jwt_authn: reject requests with a proper error if JWT has the wrong issuer when allow_missing is used. Before this change, the requests are accepted.
      // JwtMissed and JwtUnknownIssuer should be treated differently than other errors.
      // JwtMissed means not Jwt token for the required provider.
      // JwtUnknownIssuer means wrong issuer for the required provider.
        // Prefer errors which are not JwtMissed nor JwtUnknownIssuer.
        // Prefer JwtUnknownIssuer between JwtMissed and JwtUnknownIssuer.
        if ((child_status != Status::JwtMissed && child_status != Status::JwtUnknownIssuer) ||
            final_status == Status::JwtMissed) {
  EXPECT_CALL(mock_cb_, onComplete(Status::JwtUnknownIssuer));
TEST_F(AllowMissingInOrListTest, WrongIssuer) {
  EXPECT_CALL(mock_cb_, onComplete(Status::JwtUnknownIssuer));
  auto headers = Http::TestRequestHeaderMapImpl{{kExampleHeader, OtherGoodToken}};
  context_ = Verifier::createContext(headers, parent_span_, &mock_cb_);
  verifier_->verify(context_);
  // x-other JWT should be ignored.
  EXPECT_THAT(headers, JwtOutputFailedOrIgnore(kOtherHeader));
}

  EXPECT_CALL(mock_cb_, onComplete(Status::JwtUnknownIssuer));
// Test RequiresAny with two providers and allow_missing, but one returns JwtUnknownIssuer
TEST_F(GroupVerifierTest, TestRequiresAnyWithAllowMissingButUnknownIssuer) {
  EXPECT_CALL(mock_cb_, onComplete(Status::JwtUnknownIssuer));