diff -r 9ea29ac18837 -r 93ad018fb602 runtime/typemapping.py
--- a/runtime/typemapping.py	Wed Dec 01 09:54:02 2021 +0100
+++ b/runtime/typemapping.py	Thu Dec 09 10:21:45 2021 +0100
@@ -85,11 +85,22 @@
     for iectype in indexes:
         c_type, unpack_func, _pack_func = \
             TypeTranslator.get(iectype, (None, None, None))
-        if c_type is not None and buffoffset < buffsize:
-            cursor = c_void_p(buffptr + buffoffset)
+
+        cursor = c_void_p(buffptr + buffoffset)
+        if iectype == "STRING":
+            # strlen is stored in c_uint8 and sizeof(c_uint8) is 1
+            # first check we can read size
+            if (buffoffset + 1) <= buffsize:
+                size = 1 + cast(cursor,POINTER(c_type)).contents.len
+            else:
+                return None
+        else:
+            size = sizeof(c_type)
+
+        if c_type is not None and (buffoffset + size) <= buffsize:
             value = unpack_func(cast(cursor,
                                      POINTER(c_type)).contents)
-            buffoffset += sizeof(c_type) if iectype != "STRING" else len(value)+1
+            buffoffset += size
             res.append(value)
         else:
             return None