diff --git a/ChangeLog.d/serialized-data-load-hardening.txt b/ChangeLog.d/serialized-data-load-hardening.txt
new file mode 100644
index 0000000000..e068988dac
--- /dev/null
+++ b/ChangeLog.d/serialized-data-load-hardening.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Reject malformed TLS 1.3 serialized sessions instead of accepting
+     unterminated strings or extra trailing data.
+   * Reject serialized SSL contexts whose DTLS Connection ID length exceeds
+     the maximum supported size, instead of overflowing the internal buffer.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 88aaf85d29..fd67726d4d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4035,6 +4035,12 @@ static int ssl_tls13_session_load(mbedtls_ssl_session *session,
         }
 
         if (alpn_len > 0) {
+            /* The data is about to be used as a null-terminated string, so
+             * check that it actually is one. */
+            if (p[alpn_len - 1] != '\0') {
+                return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+            }
+
             int ret = mbedtls_ssl_session_set_ticket_alpn(session, (char *) p);
             if (ret != 0) {
                 return ret;
@@ -4060,11 +4066,16 @@ static int ssl_tls13_session_load(mbedtls_ssl_session *session,
             return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
         }
         if (hostname_len > 0) {
-            session->hostname = mbedtls_calloc(1, hostname_len);
-            if (session->hostname == NULL) {
-                return MBEDTLS_ERR_SSL_ALLOC_FAILED;
+            /* The data is about to be used as a null-terminated string, so
+             * check that it actually is one. */
+            if (p[hostname_len - 1] != '\0') {
+                return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+            }
+
+            int ret = mbedtls_ssl_session_set_hostname(session, (const char *) p);
+            if (ret != 0) {
+                return ret;
             }
-            memcpy(session->hostname, p, hostname_len);
             p += hostname_len;
         }
 #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
@@ -4102,6 +4113,10 @@ static int ssl_tls13_session_load(mbedtls_ssl_session *session,
     }
 #endif /* MBEDTLS_SSL_CLI_C */
 
+    if (p != end) {
+        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+    }
+
     return 0;
 
 }
@@ -5440,6 +5455,10 @@ static int ssl_context_load(mbedtls_ssl_context *ssl,
         return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
     }
 
+    if (ssl->transform->in_cid_len > sizeof(ssl->transform->in_cid)) {
+        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+    }
+
     memcpy(ssl->transform->in_cid, p, ssl->transform->in_cid_len);
     p += ssl->transform->in_cid_len;
 
@@ -5449,6 +5468,10 @@ static int ssl_context_load(mbedtls_ssl_context *ssl,
         return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
     }
 
+    if (ssl->transform->out_cid_len > sizeof(ssl->transform->out_cid)) {
+        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+    }
+
     memcpy(ssl->transform->out_cid, p, ssl->transform->out_cid_len);
     p += ssl->transform->out_cid_len;
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
diff --git a/tests/suites/test_suite_ssl.data b/tests/suites/test_suite_ssl.data
index 06e8b62303..77a5ab2244 100644
--- a/tests/suites/test_suite_ssl.data
+++ b/tests/suites/test_suite_ssl.data
@@ -3185,6 +3185,19 @@ TLS 1.3: SRV: Session serialization, load buffer size
 depends_on:MBEDTLS_SSL_PROTO_TLS1_3:MBEDTLS_SSL_SESSION_TICKETS:MBEDTLS_SSL_SRV_C
 ssl_serialize_session_load_buf_size:0:"":MBEDTLS_SSL_IS_SERVER:MBEDTLS_SSL_VERSION_TLS1_3
 
+TLS 1.3: Session serialization rejects trailing data
+depends_on:MBEDTLS_SSL_CLI_C
+ssl_tls13_session_load_rejects_bad_serialized_data:MBEDTLS_SSL_IS_CLIENT:TEST_TLS13_SESSION_LOAD_TRAILING_DATA
+
+TLS 1.3: Session serialization rejects hostname without terminator
+depends_on:MBEDTLS_SSL_CLI_C:MBEDTLS_SSL_SERVER_NAME_INDICATION
+ssl_tls13_session_load_rejects_bad_serialized_data:MBEDTLS_SSL_IS_CLIENT:TEST_TLS13_SESSION_LOAD_HOSTNAME_NO_NUL
+
+TLS 1.3: Session serialization rejects ALPN without terminator
+depends_on:MBEDTLS_SSL_SRV_C:MBEDTLS_SSL_EARLY_DATA:MBEDTLS_SSL_ALPN
+ssl_tls13_session_load_rejects_bad_serialized_data:MBEDTLS_SSL_IS_SERVER:TEST_TLS13_SESSION_LOAD_ALPN_NO_NUL
+
+
 Test configuration of EC groups through mbedtls_ssl_conf_curves()
 conf_curve:
 
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index ae7ab55366..c58231e5a1 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -22,6 +22,11 @@
 #define TEST_EARLY_DATA_NO_INITIAL_ALPN 6
 #define TEST_EARLY_DATA_NO_LATER_ALPN 7
 
+/* Mutations for ssl_tls13_session_load_rejects_bad_serialized_data */
+#define TEST_TLS13_SESSION_LOAD_TRAILING_DATA    0
+#define TEST_TLS13_SESSION_LOAD_HOSTNAME_NO_NUL  1
+#define TEST_TLS13_SESSION_LOAD_ALPN_NO_NUL      2
+
 #if (!defined(MBEDTLS_SSL_PROTO_TLS1_2)) && \
     defined(MBEDTLS_SSL_EARLY_DATA) && defined(MBEDTLS_SSL_CLI_C) && \
     defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_DEBUG_C) && \
@@ -2701,6 +2706,80 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE depends_on:MBEDTLS_SSL_PROTO_TLS1_3:MBEDTLS_SSL_SESSION_TICKETS */
+void ssl_tls13_session_load_rejects_bad_serialized_data(int endpoint_type,
+                                                        int mutation)
+{
+    mbedtls_ssl_session session, restored;
+    unsigned char *buf = NULL;
+    size_t len, bad_len, i;
+    unsigned char *field = NULL;
+    const unsigned char hostname[] = "hostname example";
+    const unsigned char alpn[] = "ALPNExample";
+    const unsigned char *string_to_corrupt = NULL;
+    size_t string_len = 0;
+
+    mbedtls_ssl_session_init(&session);
+    mbedtls_ssl_session_init(&restored);
+    USE_PSA_INIT();
+
+    TEST_EQUAL(mbedtls_test_ssl_tls13_populate_session(
+                   &session, 42, endpoint_type),  0);
+
+    TEST_EQUAL(mbedtls_ssl_session_save(&session, NULL, 0, &len),
+               MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL);
+    TEST_CALLOC(buf, len + 1);
+    TEST_EQUAL(mbedtls_ssl_session_save(&session, buf, len, &len),  0);
+
+    /* The serialized data must load successfully before we corrupt it,
+     * otherwise the test below would not prove anything. */
+    TEST_EQUAL(mbedtls_ssl_session_load(&restored, buf, len), 0);
+    mbedtls_ssl_session_free(&restored);
+    mbedtls_ssl_session_init(&restored);
+
+    bad_len = len;
+    switch (mutation) {
+        case TEST_TLS13_SESSION_LOAD_TRAILING_DATA:
+            bad_len = len + 1;
+            buf[len] = 0;
+            break;
+
+        case TEST_TLS13_SESSION_LOAD_HOSTNAME_NO_NUL:
+            string_to_corrupt = hostname;
+            string_len = sizeof(hostname);
+            break;
+
+        case TEST_TLS13_SESSION_LOAD_ALPN_NO_NUL:
+            string_to_corrupt = alpn;
+            string_len = sizeof(alpn);
+            break;
+
+        default:
+            TEST_ASSERT(0);
+    }
+
+    if (string_to_corrupt != NULL) {
+        for (i = 0; i + string_len <= len; i++) {
+            if (memcmp(buf + i, string_to_corrupt, string_len) == 0) {
+                field = buf + i;
+                break;
+            }
+        }
+        TEST_ASSERT(field != NULL);
+        field[string_len - 1] = 'X';
+    }
+
+    TEST_EQUAL(mbedtls_ssl_session_load(&restored, buf, bad_len),
+               MBEDTLS_ERR_SSL_BAD_INPUT_DATA);
+
+exit:
+    mbedtls_ssl_session_free(&session);
+    mbedtls_ssl_session_free(&restored);
+    mbedtls_free(buf);
+    USE_PSA_DONE();
+}
+/* END_CASE */
+
 /* BEGIN_CASE */
 void ssl_session_serialize_version_check(int corrupt_major,
                                          int corrupt_minor,