From ef73b3b2337fdde653600fa9b6f35f998d456c32 Mon Sep 17 00:00:00 2001
From: Juliusz Sosinowicz <juliusz@wolfssl.com>
Date: Wed, 15 Apr 2026 14:48:54 +0200
Subject: [PATCH] tests: add EMS resumption downgrade negative test (F-2915)

Covers the HandleResumeHistory check that RFC 7627 Section 5.3 requires:
if the original session used Extended Master Secret, the server MUST
abort when a resumption ClientHello is received without EMS. The new
memio test performs a TLS 1.2 handshake with EMS, saves the session,
disables EMS on a fresh client, resumes with the saved session, and
asserts the server returns EXT_MASTER_SECRET_NEEDED_E.
---
 tests/api.c              |  1 +
 tests/api/test_tls_ext.c | 50 ++++++++++++++++++++++++++++++++++++++++
 tests/api/test_tls_ext.h |  1 +
 3 files changed, 52 insertions(+)

diff --git a/tests/api.c b/tests/api.c
index 05a7688d7f..b9f2541570 100644
--- a/tests/api.c
+++ b/tests/api.c
@@ -37503,6 +37503,7 @@ TEST_CASE testCases[] = {
     TEST_DECL(test_wolfSSL_select_next_proto),
 #endif
     TEST_DECL(test_tls_ems_downgrade),
+    TEST_DECL(test_tls_ems_resumption_downgrade),
     TEST_DECL(test_wolfSSL_DisableExtendedMasterSecret),
     TEST_DECL(test_certificate_authorities_certificate_request),
     TEST_DECL(test_certificate_authorities_client_hello),
diff --git a/tests/api/test_tls_ext.c b/tests/api/test_tls_ext.c
index ad6053f727..4dd736f5eb 100644
--- a/tests/api/test_tls_ext.c
+++ b/tests/api/test_tls_ext.c
@@ -103,6 +103,56 @@ int test_tls_ems_downgrade(void)
 }
 
 
+/* F-2915: resumption of an EMS session without EMS must abort with
+ * EXT_MASTER_SECRET_NEEDED_E (RFC 7627 Section 5.3). */
+int test_tls_ems_resumption_downgrade(void)
+{
+    EXPECT_DECLS;
+#if !defined(WOLFSSL_NO_TLS12) && defined(HAVE_EXTENDED_MASTER) && \
+        defined(HAVE_MANUAL_MEMIO_TESTS_DEPENDENCIES) && \
+        !defined(NO_SESSION_CACHE)
+    struct test_memio_ctx test_ctx;
+    WOLFSSL_CTX *ctx_c = NULL;
+    WOLFSSL_CTX *ctx_s = NULL;
+    WOLFSSL *ssl_c = NULL;
+    WOLFSSL *ssl_s = NULL;
+    WOLFSSL_SESSION *session = NULL;
+
+    XMEMSET(&test_ctx, 0, sizeof(test_ctx));
+
+    ExpectIntEQ(test_memio_setup(&test_ctx, &ctx_c, &ctx_s, &ssl_c, &ssl_s,
+            wolfTLSv1_2_client_method, wolfTLSv1_2_server_method), 0);
+    ExpectIntEQ(test_memio_do_handshake(ssl_c, ssl_s, 10, NULL), 0);
+
+    ExpectNotNull(session = wolfSSL_get1_session(ssl_c));
+
+    wolfSSL_free(ssl_c);
+    ssl_c = NULL;
+    wolfSSL_free(ssl_s);
+    ssl_s = NULL;
+    test_memio_clear_buffer(&test_ctx, 0);
+    test_memio_clear_buffer(&test_ctx, 1);
+
+    ExpectIntEQ(test_memio_setup(&test_ctx, &ctx_c, &ctx_s, &ssl_c, &ssl_s,
+            wolfTLSv1_2_client_method, wolfTLSv1_2_server_method), 0);
+    ExpectIntEQ(wolfSSL_set_session(ssl_c, session), WOLFSSL_SUCCESS);
+    /* Drop EMS from the resumption ClientHello to simulate a downgrade. */
+    ExpectIntEQ(wolfSSL_DisableExtendedMasterSecret(ssl_c), WOLFSSL_SUCCESS);
+
+    ExpectIntNE(test_memio_do_handshake(ssl_c, ssl_s, 10, NULL), 0);
+    ExpectIntEQ(wolfSSL_get_error(ssl_s, 0),
+            WC_NO_ERR_TRACE(EXT_MASTER_SECRET_NEEDED_E));
+
+    wolfSSL_SESSION_free(session);
+    wolfSSL_free(ssl_c);
+    wolfSSL_free(ssl_s);
+    wolfSSL_CTX_free(ctx_c);
+    wolfSSL_CTX_free(ctx_s);
+#endif
+    return EXPECT_RESULT();
+}
+
+
 int test_wolfSSL_DisableExtendedMasterSecret(void)
 {
     EXPECT_DECLS;
diff --git a/tests/api/test_tls_ext.h b/tests/api/test_tls_ext.h
index ec7a5223be..8d9d8fcb9f 100644
--- a/tests/api/test_tls_ext.h
+++ b/tests/api/test_tls_ext.h
@@ -23,6 +23,7 @@
 #define TESTS_API_TEST_TLS_EXT_H
 
 int test_tls_ems_downgrade(void);
+int test_tls_ems_resumption_downgrade(void);
 int test_wolfSSL_DisableExtendedMasterSecret(void);
 int test_certificate_authorities_certificate_request(void);
 int test_certificate_authorities_client_hello(void);