diff --git a/ChangeLog.d/tls13-add-missing-overread-check.txt b/ChangeLog.d/tls13-add-missing-overread-check.txt
new file mode 100644
index 0000000..4552cd7
--- /dev/null
+++ b/ChangeLog.d/tls13-add-missing-overread-check.txt
@@ -0,0 +1,8 @@
+Security
+    * Fix a buffer overread in TLS 1.3 Certificate parsing. An unauthenticated
+      client or server could cause an MbedTLS server or client to overread up
+      to 64 kBytes of data and potentially overread the input buffer by that
+      amount minus the size of the input buffer. As overread data undergoes
+      various checks, the likelihood of reaching the boundary of the input
+      buffer is rather small but increases as its size
+      MBEDTLS_SSL_IN_CONTENT_LEN decreases.
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 1280241..c17fa20 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -381,11 +381,36 @@
  * \return       Zero if the needed space is available in the buffer, non-zero
  *               otherwise.
  */
+#if ! defined(MBEDTLS_TEST_HOOKS)
 static inline int mbedtls_ssl_chk_buf_ptr( const uint8_t *cur,
                                            const uint8_t *end, size_t need )
 {
     return( ( cur > end ) || ( need > (size_t)( end - cur ) ) );
 }
+#else
+typedef struct
+{
+    const uint8_t *cur;
+    const uint8_t *end;
+    size_t need;
+} mbedtls_ssl_chk_buf_ptr_args;
+
+void mbedtls_ssl_set_chk_buf_ptr_fail_args(
+    const uint8_t *cur, const uint8_t *end, size_t need );
+void mbedtls_ssl_reset_chk_buf_ptr_fail_args( void );
+int mbedtls_ssl_cmp_chk_buf_ptr_fail_args( mbedtls_ssl_chk_buf_ptr_args *args );
+
+static inline int mbedtls_ssl_chk_buf_ptr( const uint8_t *cur,
+                                           const uint8_t *end, size_t need )
+{
+    if( ( cur > end ) || ( need > (size_t)( end - cur ) ) )
+    {
+        mbedtls_ssl_set_chk_buf_ptr_fail_args( cur, end, need );
+        return( 1 );
+    }
+    return( 0 );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
 
 /**
  * \brief        This macro checks if the remaining size in a buffer is
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 668b5ec..55b7f85 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -58,6 +58,30 @@
 #include "mbedtls/oid.h"
 #endif
 
+#if defined(MBEDTLS_TEST_HOOKS)
+static mbedtls_ssl_chk_buf_ptr_args chk_buf_ptr_fail_args;
+
+void mbedtls_ssl_set_chk_buf_ptr_fail_args(
+    const uint8_t *cur, const uint8_t *end, size_t need )
+{
+    chk_buf_ptr_fail_args.cur = cur;
+    chk_buf_ptr_fail_args.end = end;
+    chk_buf_ptr_fail_args.need = need;
+}
+
+void mbedtls_ssl_reset_chk_buf_ptr_fail_args( void )
+{
+    memset( &chk_buf_ptr_fail_args, 0, sizeof( chk_buf_ptr_fail_args ) );
+}
+
+int mbedtls_ssl_cmp_chk_buf_ptr_fail_args( mbedtls_ssl_chk_buf_ptr_args *args )
+{
+    return( ( chk_buf_ptr_fail_args.cur  != args->cur  ) ||
+            ( chk_buf_ptr_fail_args.end  != args->end  ) ||
+            ( chk_buf_ptr_fail_args.need != args->need ) );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
 
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
@@ -1103,6 +1127,8 @@
         memset( ssl->in_buf, 0, in_buf_len );
     }
 
+    ssl->send_alert = 0;
+
     /* Reset outgoing message writing */
     ssl->out_msgtype = 0;
     ssl->out_msglen  = 0;
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index c7e00a9..7d0559b 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -31,6 +31,7 @@
 #include <string.h>
 
 #include "ssl_misc.h"
+#include "ssl_tls13_invasive.h"
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
 
@@ -391,9 +392,10 @@
 
 /* Parse certificate chain send by the server. */
 MBEDTLS_CHECK_RETURN_CRITICAL
-static int ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
-                                        const unsigned char *buf,
-                                        const unsigned char *end )
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t certificate_request_context_len = 0;
@@ -444,6 +446,7 @@
 
     mbedtls_x509_crt_init( ssl->session_negotiate->peer_cert );
 
+    MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, certificate_list_len );
     certificate_list_end = p + certificate_list_len;
     while( p < certificate_list_end )
     {
@@ -524,9 +527,10 @@
 }
 #else
 MBEDTLS_CHECK_RETURN_CRITICAL
-static int ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
-                                        const unsigned char *buf,
-                                        const unsigned char *end )
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end )
 {
     ((void) ssl);
     ((void) buf);
@@ -657,7 +661,8 @@
      * with details encoded in the verification flags. All other kinds
      * of error codes, including those from the user provided f_vrfy
      * functions, are treated as fatal and lead to a failure of
-     * ssl_tls13_parse_certificate even if verification was optional. */
+     * mbedtls_ssl_tls13_parse_certificate even if verification was optional.
+     */
     if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL &&
         ( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED ||
           ret == MBEDTLS_ERR_SSL_BAD_CERTIFICATE ) )
@@ -735,8 +740,8 @@
                           &buf, &buf_len ) );
 
     /* Parse the certificate chain sent by the peer. */
-    MBEDTLS_SSL_PROC_CHK( ssl_tls13_parse_certificate( ssl, buf,
-                                                       buf + buf_len ) );
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_parse_certificate( ssl, buf,
+                                                               buf + buf_len ) );
     /* Validate the certificate chain and set the verification results. */
     MBEDTLS_SSL_PROC_CHK( ssl_tls13_validate_certificate( ssl ) );
 
diff --git a/library/ssl_tls13_invasive.h b/library/ssl_tls13_invasive.h
index 4e39f90..55fc958 100644
--- a/library/ssl_tls13_invasive.h
+++ b/library/ssl_tls13_invasive.h
@@ -80,6 +80,10 @@
                                       const unsigned char *info, size_t info_len,
                                       unsigned char *okm, size_t okm_len );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end );
 #endif /* MBEDTLS_TEST_HOOKS */
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 6144c2f..27c211f 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2904,6 +2904,18 @@
     if_build_succeeded tests/ssl-opt.sh
 }
 
+component_test_tls13_only_with_hooks () {
+    msg "build: default config with MBEDTLS_SSL_PROTO_TLS1_3 and MBEDTLS_TEST_HOOKS, without MBEDTLS_SSL_PROTO_TLS1_2"
+    scripts/config.py set MBEDTLS_TEST_HOOKS
+    make CFLAGS="'-DMBEDTLS_USER_CONFIG_FILE=\"../tests/configs/tls13-only.h\"'"
+
+    msg "test: default config with MBEDTLS_SSL_PROTO_TLS1_3 enabled, without MBEDTLS_SSL_PROTO_TLS1_2"
+    if_build_succeeded make test
+
+    msg "ssl-opt.sh (TLS 1.3)"
+    if_build_succeeded tests/ssl-opt.sh
+}
+
 component_test_tls13 () {
     msg "build: default config with MBEDTLS_SSL_PROTO_TLS1_3 enabled, without padding"
     scripts/config.py set MBEDTLS_SSL_PROTO_TLS1_3
diff --git a/tests/suites/test_suite_ssl.data b/tests/suites/test_suite_ssl.data
index e82c66e..8ce81d0 100644
--- a/tests/suites/test_suite_ssl.data
+++ b/tests/suites/test_suite_ssl.data
@@ -3381,3 +3381,6 @@
 
 Cookie parsing: one byte overread
 cookie_parsing:"16fefd0000000000000000002F010000de000000000000011efefd7b7272727272727272727272727272727272727272727272727272727272727d0001":MBEDTLS_ERR_SSL_DECODE_ERROR
+
+TLS 1.3 srv Certificate msg - wrong vector lengths
+tls13_server_certificate_msg_invalid_vector_len
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 2ab2aaa..59c69c6 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -105,6 +105,23 @@
   opts->cli_log_fun = NULL;
   opts->resize_buffers = 1;
 }
+
+#if defined(MBEDTLS_TEST_HOOKS)
+static void set_chk_buf_ptr_args(
+    mbedtls_ssl_chk_buf_ptr_args *args,
+    unsigned char *cur, unsigned char *end, size_t need )
+{
+    args->cur = cur;
+    args->end = end;
+    args->need = need;
+}
+
+static void reset_chk_buf_ptr_args( mbedtls_ssl_chk_buf_ptr_args *args )
+{
+    memset( args, 0, sizeof( *args ) );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
+
 /*
  * Buffer structure for custom I/O callbacks.
  */
@@ -2307,6 +2324,119 @@
 }
 #endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_ENTROPY_C && MBEDTLS_CTR_DRBG_C */
 
+#if defined(MBEDTLS_TEST_HOOKS)
+/*
+ * Tweak vector lengths in a TLS 1.3 Certificate message
+ *
+ * \param[in]       buf    Buffer containing the Certificate message to tweak
+ * \param[in]]out]  end    End of the buffer to parse
+ * \param           tweak  Tweak identifier (from 1 to the number of tweaks).
+ * \param[out]  expected_result  Error code expected from the parsing function
+ * \param[out]  args  Arguments of the MBEDTLS_SSL_CHK_BUF_READ_PTR call that
+ *                    is expected to fail. All zeroes if no
+ *                    MBEDTLS_SSL_CHK_BUF_READ_PTR failure is expected.
+ */
+int tweak_tls13_certificate_msg_vector_len(
+    unsigned char *buf, unsigned char **end, int tweak,
+    int *expected_result, mbedtls_ssl_chk_buf_ptr_args *args )
+{
+/*
+ * The definition of the tweaks assume that the certificate list contains only
+ * one certificate.
+ */
+
+/*
+ * struct {
+ *     opaque cert_data<1..2^24-1>;
+ *     Extension extensions<0..2^16-1>;
+ * } CertificateEntry;
+ *
+ * struct {
+ *     opaque certificate_request_context<0..2^8-1>;
+ *     CertificateEntry certificate_list<0..2^24-1>;
+ * } Certificate;
+ */
+    unsigned char *p_certificate_request_context_len = buf;
+    size_t certificate_request_context_len = buf[0];
+
+    unsigned char *p_certificate_list_len = buf + 1 + certificate_request_context_len;
+    unsigned char *certificate_list = p_certificate_list_len + 3;
+    size_t certificate_list_len = MBEDTLS_GET_UINT24_BE( p_certificate_list_len, 0 );
+
+    unsigned char *p_cert_data_len = certificate_list;
+    unsigned char *cert_data = p_cert_data_len + 3;
+    size_t cert_data_len = MBEDTLS_GET_UINT24_BE( p_cert_data_len, 0 );
+
+    unsigned char *p_extensions_len = cert_data + cert_data_len;
+    unsigned char *extensions = p_extensions_len + 2;
+    size_t extensions_len = MBEDTLS_GET_UINT16_BE( p_extensions_len, 0 );
+
+    *expected_result = MBEDTLS_ERR_SSL_DECODE_ERROR;
+
+    switch( tweak )
+    {
+        case 1:
+        /* Failure when checking if the certificate request context length and
+         * certificate list length can be read
+         */
+        *end = buf + 3;
+        set_chk_buf_ptr_args( args, buf, *end, 4 );
+        break;
+
+        case 2:
+        /* Invalid certificate request context length.
+         */
+        *p_certificate_request_context_len =
+            certificate_request_context_len + 1;
+        reset_chk_buf_ptr_args( args );
+        break;
+
+        case 3:
+        /* Failure when checking if certificate_list data can be read. */
+        MBEDTLS_PUT_UINT24_BE( certificate_list_len + 1,
+                               p_certificate_list_len, 0 );
+        set_chk_buf_ptr_args( args, certificate_list, *end,
+                              certificate_list_len + 1 );
+        break;
+
+        case 4:
+        /* Failure when checking if the cert_data length can be read. */
+        MBEDTLS_PUT_UINT24_BE( 2, p_certificate_list_len, 0 );
+        set_chk_buf_ptr_args( args, p_cert_data_len, certificate_list + 2, 3 );
+        break;
+
+        case 5:
+        /* Failure when checking if cert_data data can be read. */
+        MBEDTLS_PUT_UINT24_BE( certificate_list_len - 3 + 1,
+                               p_cert_data_len, 0 );
+        set_chk_buf_ptr_args( args, cert_data,
+                              certificate_list + certificate_list_len,
+                              certificate_list_len - 3 + 1 );
+        break;
+
+        case 6:
+        /* Failure when checking if the extensions length can be read. */
+        MBEDTLS_PUT_UINT24_BE( certificate_list_len - extensions_len - 1,
+                               p_certificate_list_len, 0 );
+        set_chk_buf_ptr_args( args, p_extensions_len,
+            certificate_list + certificate_list_len - extensions_len - 1, 2 );
+        break;
+
+        case 7:
+        /* Failure when checking if extensions data can be read. */
+        MBEDTLS_PUT_UINT16_BE( extensions_len + 1, p_extensions_len, 0 );
+
+        set_chk_buf_ptr_args( args, extensions,
+            certificate_list + certificate_list_len, extensions_len + 1 );
+        break;
+
+        default:
+        return( -1 );
+    }
+
+    return( 0 );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -5708,3 +5838,87 @@
     USE_PSA_DONE( );
 }
 /* END_CASE */
+/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS:MBEDTLS_SSL_PROTO_TLS1_3:!MBEDTLS_SSL_PROTO_TLS1_2:MBEDTLS_SSL_CLI_C:MBEDTLS_SSL_SRV_C:MBEDTLS_X509_CRT_PARSE_C:MBEDTLS_ECP_DP_SECP384R1_ENABLED */
+void tls13_server_certificate_msg_invalid_vector_len( )
+{
+    int ret = -1;
+    mbedtls_endpoint client_ep, server_ep;
+    unsigned char *buf, *end;
+    size_t buf_len;
+    int step = 0;
+    int expected_result;
+    mbedtls_ssl_chk_buf_ptr_args expected_chk_buf_ptr_args;
+
+    /*
+     * Test set-up
+     */
+    USE_PSA_INIT( );
+
+    ret = mbedtls_endpoint_init( &client_ep, MBEDTLS_SSL_IS_CLIENT,
+                                 MBEDTLS_PK_ECDSA, NULL, NULL, NULL, NULL );
+    TEST_EQUAL( ret, 0 );
+
+    ret = mbedtls_endpoint_init( &server_ep, MBEDTLS_SSL_IS_SERVER,
+                                 MBEDTLS_PK_ECDSA, NULL, NULL, NULL, NULL );
+    TEST_EQUAL( ret, 0 );
+
+    ret = mbedtls_mock_socket_connect( &(client_ep.socket),
+                                       &(server_ep.socket), 1024 );
+    TEST_EQUAL( ret, 0 );
+
+    while( 1 )
+    {
+        mbedtls_test_set_step( ++step );
+
+        ret = mbedtls_move_handshake_to_state( &(server_ep.ssl),
+                                               &(client_ep.ssl),
+                                               MBEDTLS_SSL_CERTIFICATE_VERIFY );
+        TEST_EQUAL( ret, 0 );
+
+        ret = mbedtls_ssl_flush_output( &(server_ep.ssl) );
+        TEST_EQUAL( ret, 0 );
+
+        ret = mbedtls_move_handshake_to_state( &(client_ep.ssl),
+                                               &(server_ep.ssl),
+                                               MBEDTLS_SSL_SERVER_CERTIFICATE );
+        TEST_EQUAL( ret, 0 );
+
+        ret = mbedtls_ssl_tls13_fetch_handshake_msg( &(client_ep.ssl),
+                                                     MBEDTLS_SSL_HS_CERTIFICATE,
+                                                     &buf, &buf_len );
+        TEST_EQUAL( ret, 0 );
+
+        end = buf + buf_len;
+
+        /*
+         * Tweak server Certificate message and parse it.
+         */
+
+        ret = tweak_tls13_certificate_msg_vector_len(
+            buf, &end, step, &expected_result, &expected_chk_buf_ptr_args );
+
+        if( ret != 0 )
+            break;
+
+        ret = mbedtls_ssl_tls13_parse_certificate( &(client_ep.ssl), buf, end );
+        TEST_EQUAL( ret, expected_result );
+
+        TEST_ASSERT( mbedtls_ssl_cmp_chk_buf_ptr_fail_args(
+                         &expected_chk_buf_ptr_args ) == 0 );
+
+        mbedtls_ssl_reset_chk_buf_ptr_fail_args( );
+
+        ret = mbedtls_ssl_session_reset( &(client_ep.ssl) );
+        TEST_EQUAL( ret, 0 );
+
+        ret = mbedtls_ssl_session_reset( &(server_ep.ssl) );
+        TEST_EQUAL( ret, 0 );
+    }
+
+exit:
+    mbedtls_ssl_reset_chk_buf_ptr_fail_args( );
+    mbedtls_endpoint_free( &client_ep, NULL );
+    mbedtls_endpoint_free( &server_ep, NULL );
+    USE_PSA_DONE( );
+}
+/* END_CASE */