diff --git a/chrome/browser/enterprise/profile_management/oidc_auth_response_capture_navigation_throttle.cc b/chrome/browser/enterprise/profile_management/oidc_auth_response_capture_navigation_throttle.cc
index ef58d81592120..db1c39d0258f8 100644
--- a/chrome/browser/enterprise/profile_management/oidc_auth_response_capture_navigation_throttle.cc
+++ b/chrome/browser/enterprise/profile_management/oidc_auth_response_capture_navigation_throttle.cc
@@ -264,6 +264,16 @@ OidcAuthResponseCaptureNavigationThrottle::AttemptToTriggerUrlInterception() {
 
     for (const auto& chain_url : navigation_handle()->GetRedirectChain()) {
       if (!GetOidcEnrollmentUrlMatcher()->MatchURL(chain_url).empty()) {
+        // [POC INSTRUMENTATION] Prove subdomain-wildcard / any-hop bypass.
+        // The matcher was built from kEntraMcasHost="https://mcas.ms" via
+        // AddAllowFiltersWithLimit -> match_subdomains=true, so ANY *.mcas.ms
+        // host satisfies this check. The loop also accepts ANY hop in the
+        // chain, not just the immediate predecessor of the enrollment URL.
+        LOG(ERROR) << "[POC] REDIRECT-CHAIN BYPASS: trusted-host matcher "
+                      "accepted chain URL '"
+                   << chain_url.spec()
+                   << "' (host=" << chain_url.host()
+                   << ") -- subdomain wildcard / any-hop check passed";
         accept_redirect = true;
         break;
       }
@@ -346,6 +356,16 @@ OidcAuthResponseCaptureNavigationThrottle::AttemptToTriggerUrlInterception() {
     return CANCEL_AND_IGNORE;
   }
 
+  // [POC INSTRUMENTATION] CWE-347: prove that jwt_sections[2] (the signature)
+  // is never cryptographically verified. Only jwt_sections[1] (payload) is
+  // base64-decoded above. The signature could be ANY string and this code
+  // path proceeds. An attacker can forge arbitrary iss/sub claims.
+  LOG(ERROR) << "[POC] CWE-347 UNSIGNED-JWT ACCEPTED: signature section = '"
+             << jwt_sections[2]
+             << "' (len=" << jwt_sections[2].size()
+             << ") -- this signature was NEVER cryptographically verified";
+  LOG(ERROR) << "[POC] decoded payload from unsigned JWT: " << json_payload;
+
   interception_triggered_ = true;
   data_decoder::DataDecoder::ParseJsonIsolated(
       json_payload,
@@ -401,6 +421,17 @@ void OidcAuthResponseCaptureNavigationThrottle::RegisterWithOidcTokens(
   RecordOidcInterceptionFunnelStep(
       OidcInterceptionFunnelStep::kSuccessfulInfoParsed);
 
+  // [POC INSTRUMENTATION] Prove attacker-controlled identity from the
+  // unsigned JWT is forwarded into the enrollment interceptor. These values
+  // become unique_user_identifier_ in oidc_authentication_signin_interceptor.cc
+  // and the trusted browser-chrome enrollment dialog is shown for them.
+  LOG(ERROR) << "[POC] *** VULNERABILITY CONFIRMED *** "
+                "MaybeInterceptOidcAuthentication invoked with "
+                "ATTACKER-CONTROLLED identity from UNSIGNED JWT: "
+                "iss='" << *issuer_id << "' sub='" << *subject_id
+             << "' -- next step is ShowOidcInterceptionDialog "
+                "(trusted browser-native modal)";
+
   interceptor->MaybeInterceptOidcAuthentication(
       navigation_handle()->GetWebContents(), tokens, *issuer_id, *subject_id,
       std::string(),
diff --git a/chrome/browser/enterprise/signin/oidc_authentication_signin_interceptor.cc b/chrome/browser/enterprise/signin/oidc_authentication_signin_interceptor.cc
index 5f8b3f299cef2..11d9b4f55a589 100644
--- a/chrome/browser/enterprise/signin/oidc_authentication_signin_interceptor.cc
+++ b/chrome/browser/enterprise/signin/oidc_authentication_signin_interceptor.cc
@@ -135,6 +135,13 @@ void OidcAuthenticationSigninInterceptor::MaybeInterceptOidcAuthentication(
   unique_user_identifier_ = base::StringPrintf(
       kUniqueIdentifierTemplate, issuer_id.c_str(), subject_id.c_str());
 
+  // [POC INSTRUMENTATION] The unique_user_identifier_ used for profile
+  // matching and creation is built directly from the unsigned JWT's iss/sub.
+  LOG(ERROR) << "[POC] OidcAuthenticationSigninInterceptor: "
+                "unique_user_identifier_ set to '"
+             << unique_user_identifier_
+             << "' (built from unverified iss/sub) -- proceeding to dialog";
+
   CHECK(!switch_to_entry_);
   base::FilePath profile_path = profile_->GetPath();
   for (const auto* entry : g_browser_process->profile_manager()
@@ -201,6 +208,18 @@ void OidcAuthenticationSigninInterceptor::MaybeInterceptOidcAuthentication(
     return;
   }
 
+  // [POC INSTRUMENTATION] We are about to call ShowOidcInterceptionDialog ->
+  // DiceWebSigninInterceptorDelegate::ShowOidcInterceptionDialog ->
+  // ShowModalManagedUserNoticeDialog with profile_creation_required_by_policy
+  // = true. This is the trusted browser-chrome modal. No DM-server round-trip
+  // has happened yet -- the dialog appears BEFORE any server-side validation
+  // of the (unsigned, forged) tokens.
+  LOG(ERROR) << "[POC] *** TRUSTED DIALOG TRIGGERED *** "
+                "delegate_->ShowOidcInterceptionDialog about to be called "
+                "for forged identity '" << unique_user_identifier_
+             << "' -- on a desktop with display, the user now sees a "
+                "browser-native 'Your organization requires a profile' modal";
+
   // TODO(374765466): Simplify this logic by creating a function that can call
   // one of the following callbacks according to an argument, then passing
   // this single callback instead of three separate callbacks.