verify length limit for supported version ext

add length check to tls extensions

Author: rlm2002

src/tls.c

@@ -6972,8 +6972,10 @@ int TLSX_SupportedVersions_Parse(const WOLFSSL* ssl, const byte* input,
         int set = 0;
 
         /* Must contain a length and at least one version. */
-        if (length < OPAQUE8_LEN + OPAQUE16_LEN || (length & 1) != 1)
+        if (length < OPAQUE8_LEN + OPAQUE16_LEN || (length & 1) != 1
+            || length > MAX_SV_EXT_LEN) {
             return BUFFER_ERROR;
+        }
 
         len = *input;
 
@@ -9963,10 +9965,13 @@ int TLSX_KeyShare_Parse_ClientHello(const WOLFSSL* ssl,
     if (length < OPAQUE16_LEN)
         return BUFFER_ERROR;
 
-    /* ClientHello contains zero or more key share entries. */
+    /* ClientHello contains zero or more key share entries. Limits extension
+     * length to 2^16-1 and subtracting 4 bytes for header size per RFC 8446 */
     ato16(input, &len);
-    if (len != length - OPAQUE16_LEN)
+    if ((len != length - OPAQUE16_LEN) ||
+         length > (MAX_EXT_DATA_LEN - HELLO_EXT_SZ)) {
         return BUFFER_ERROR;
+    }
     offset += OPAQUE16_LEN;
 
     while (offset < (int)length) {

wolfssl/internal.h

@@ -1668,6 +1668,12 @@ enum Misc {
     MAX_REQUEST_SZ      = 256, /* Maximum cert req len (no auth yet */
     SESSION_FLUSH_COUNT = 256, /* Flush session cache unless user turns off */
     TLS_MAX_PAD_SZ      = 255, /* Max padding in TLS */
+    MAX_EXT_DATA_LEN    = 65535,
+                          /* Max extension data length <0..2^16-1> RFC 8446
+                           * Section 4.2 */
+    MAX_SV_EXT_LEN      = 255,
+                          /* Max supported_versions extension length
+                           * <2..254> RFC 8446 Section 4.2.1.*/
 
 #if defined(HAVE_NULL_CIPHER) && defined(WOLFSSL_TLS13)
     #if defined(WOLFSSL_SHA384) && WC_MAX_SYM_KEY_SIZE < 48