From fc40907a5866310f620d22c7f76ba5c148fafc07 Mon Sep 17 00:00:00 2001
From: Jacek Kowalski <Jacek@jacekk.info>
Date: Tue, 03 Nov 2026 21:04:42 +0000
Subject: [PATCH] Return CAS error instead of HTTP 500 on malformed tickets

---
 src/main/java/org/keycloak/protocol/cas/endpoints/ProxyEndpoint.java |   21 ++++++++++++++++++++-
 1 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/src/main/java/org/keycloak/protocol/cas/endpoints/ProxyEndpoint.java b/src/main/java/org/keycloak/protocol/cas/endpoints/ProxyEndpoint.java
index 41f81e0..82fb36d 100644
--- a/src/main/java/org/keycloak/protocol/cas/endpoints/ProxyEndpoint.java
+++ b/src/main/java/org/keycloak/protocol/cas/endpoints/ProxyEndpoint.java
@@ -5,12 +5,15 @@
 import jakarta.ws.rs.core.MultivaluedMap;
 import jakarta.ws.rs.core.Response;
 import org.jboss.resteasy.annotations.cache.NoCache;
+import org.keycloak.events.Errors;
 import org.keycloak.events.EventBuilder;
 import org.keycloak.events.EventType;
 import org.keycloak.models.*;
 import org.keycloak.protocol.cas.CASLoginProtocol;
+import org.keycloak.protocol.cas.representations.CASErrorCode;
 import org.keycloak.protocol.cas.representations.CASServiceResponse;
 import org.keycloak.protocol.cas.utils.CASValidationException;
+import org.keycloak.protocol.cas.utils.RedirectUtils;
 import org.keycloak.protocol.cas.utils.ContentTypeHelper;
 import org.keycloak.protocol.cas.utils.ServiceResponseHelper;
 
@@ -33,13 +36,29 @@
             checkSsl();
             checkRealm();
             checkTicket(pgt, CASLoginProtocol.PROXY_GRANTING_TICKET_PREFIX, false);
+            String verifiedTargetService = checkTargetService(targetService);
             event.success();
-            return successResponse(getPT(this.session, clientSession, targetService));
+            return successResponse(getPT(this.session, clientSession, verifiedTargetService));
         } catch (CASValidationException e) {
             return errorResponse(e);
         }
     }
 
+    private String checkTargetService(String targetService) {
+        if (targetService == null) {
+            event.error(Errors.INVALID_REQUEST);
+            throw new CASValidationException(CASErrorCode.INVALID_REQUEST, "Missing parameter: " + CASLoginProtocol.TARGET_SERVICE_PARAM, Response.Status.BAD_REQUEST);
+        }
+
+        ClientModel targetClient = findClient(targetService);
+        if (targetClient == null || !targetClient.isEnabled()) {
+            event.error(Errors.CLIENT_NOT_FOUND);
+            throw new CASValidationException(CASErrorCode.INVALID_SERVICE, "Target service not allowed", Response.Status.BAD_REQUEST);
+        }
+
+        return RedirectUtils.verifyRedirectUri(session, targetService, targetClient);
+    }
+
     protected Response successResponse(String pt) {
         CASServiceResponse serviceResponse = ServiceResponseHelper.createProxySuccess(pt);
         return prepare(Response.Status.OK, serviceResponse);

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