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[OID4VCI] Fix credential request decryption alg downgrade vulnerability #50960

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[OID4VCI] Fix credential request decryption alg downgrade vulnerability #50960

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12 changes: 12 additions & 0 deletions services/src/main/java/org/keycloak/protocol/oid4vc/issuance/OID4VCIssuerEndpoint.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1218,6 +1218,18 @@ private CredentialRequest decryptCredentialRequest(String jweString, CredentialR
}
KeyWrapper keyWrapper = matchingKeys.get(0);

String alg = header.getAlgorithm();
if (alg == null) {
throw new JWEException("Missing alg in JWE header");
}
if (!alg.equals(keyWrapper.getAlgorithm())) {
String errorMessage = String.format(
"Key management algorithm mismatch: header alg=%s does not match key algorithm=%s for kid=%s",
alg, keyWrapper.getAlgorithm(), kid);
LOGGER.debug(errorMessage);
throw new JWEException(ErrorType.INVALID_ENCRYPTION_PARAMETERS.getValue());
}

// Set the decryption key
jwe.getKeyStorage().setDecryptionKey(keyWrapper.getPrivateKey());

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29 changes: 29 additions & 0 deletions tests/base/src/test/java/org/keycloak/tests/oid4vc/OID4VCIssuerEndpointEncryptionTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -39,12 +39,14 @@

import static org.keycloak.OID4VCConstants.OPENID_CREDENTIAL;
import static org.keycloak.jose.jwe.JWEConstants.A256GCM;
import static org.keycloak.jose.jwe.JWEConstants.RSA1_5;
import static org.keycloak.protocol.oid4vc.issuance.OID4VCIssuerWellKnownProvider.ATTR_REQUEST_ENCRYPTION_REQUIRED;
import static org.keycloak.protocol.oid4vc.issuance.OID4VCIssuerWellKnownProvider.ATTR_RESPONSE_ENCRYPTION_REQUIRED;
import static org.keycloak.tests.oid4vc.OID4VCProofTestUtils.generateJwtProof;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertNotEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.fail;
Expand Down Expand Up @@ -131,6 +133,33 @@ void testEncryptedCredentialRequestWithCompression() throws Exception {
}
}

@Test
void testRequestCredentialRejectsKeyManagementAlgorithmDowngrade() throws Exception {
FlowData flow = prepareFlow();
Map<String, Object> jwkPair = generateRsaJwkWithPrivateKey();
JWK responseJwk = (JWK) jwkPair.get("jwk");

CredentialRequest credentialRequest = new CredentialRequest()
.setCredentialIdentifier(flow.credentialIdentifier())
.setProofs(new Proofs().setJwt(List.of(generateJwtProof(flow.issuer(), flow.cNonce()))))
.setCredentialResponseEncryption(new CredentialResponseEncryption().setEnc(A256GCM).setJwk(responseJwk));

// The issuer advertises this key with an RSA-OAEP family algorithm, never legacy RSA1_5.
// Encrypt the same request to the same RSA public key (same kid), but downgrade the JWE
// header to alg=RSA1_5.
JWK requestEncryptionJwk = flow.issuerMetadata().getCredentialRequestEncryption().getJwks().getKeys()[0];
assertNotEquals(RSA1_5, requestEncryptionJwk.getAlgorithm());

var response = oauth.oid4vc()
.credentialRequest(credentialRequest)
.bearerToken(flow.token())
.encryptRequest(requestEncryptionJwk, false, RSA1_5)
.send();

assertEquals(400, response.getStatusCode());
assertEquals(ErrorType.INVALID_ENCRYPTION_PARAMETERS.getValue(), response.getError());
}

@Test
void testRequestCredentialWithIncompleteEncryptionParams() throws Throwable {
String token = getBearerToken(oauth, client, jwtTypeCredentialScope.getName());
Expand Down
16 changes: 13 additions & 3 deletions ...hared/src/main/java/org/keycloak/testsuite/util/oauth/oid4vc/Oid4vcCredentialRequest.java
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Expand Up @@ -70,9 +70,18 @@ public Oid4vcCredentialRequest payload(String payload, ContentType contentType)
* Encrypt current credential request as compact JWE and send with application/jwt.
*/
public Oid4vcCredentialRequest encryptRequest(JWK issuerEncryptionJwk, boolean useDeflateCompression) {
return encryptRequest(issuerEncryptionJwk, useDeflateCompression, null);
}

/**
* Encrypt current credential request as compact JWE and send with application/jwt, forcing the
* given key management algorithm in the JWE header regardless of the issuer key's advertised
* algorithm. Passing {@code algorithmOverride} exercises algorithm-downgrade scenarios.
*/
public Oid4vcCredentialRequest encryptRequest(JWK issuerEncryptionJwk, boolean useDeflateCompression, String algorithmOverride) {
try {
String requestPayload = JsonSerialization.valueAsString(credRequest);
String jwePayload = encryptPayload(requestPayload, issuerEncryptionJwk, useDeflateCompression);
String jwePayload = encryptPayload(requestPayload, issuerEncryptionJwk, useDeflateCompression, algorithmOverride);
return payload(jwePayload, ContentType.create("application/jwt", StandardCharsets.UTF_8));
} catch (Exception e) {
throw new RuntimeException("Failed to encrypt credential request", e);
Expand Down Expand Up @@ -102,11 +111,12 @@ protected Oid4vcCredentialResponse toResponse(CloseableHttpResponse response) th
return new Oid4vcCredentialResponse(response);
}

private static String encryptPayload(String payload, JWK issuerEncJwk, boolean useCompression) throws Exception {
private static String encryptPayload(String payload, JWK issuerEncJwk, boolean useCompression, String algorithmOverride) throws Exception {
PublicKey publicKey = JWKParser.create(issuerEncJwk).toPublicKey();
String algorithm = algorithmOverride != null ? algorithmOverride : issuerEncJwk.getAlgorithm();
JWEHeader.JWEHeaderBuilder builder = new JWEHeader.JWEHeaderBuilder()
.keyId(issuerEncJwk.getKeyId())
.algorithm(issuerEncJwk.getAlgorithm())
.algorithm(algorithm)
.encryptionAlgorithm("A256GCM")
.type("JWT");
if (useCompression) {
Expand Down
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