Replaced all uses of sprintf() with the safer snprintf(). It is just a

precaution to prevent mistakes to lead to buffer overflows.

lib/formdata.c

@@ -846,7 +846,7 @@ static CURLcode AddFormDataf(struct FormData **formp,
   char s[4096];
   va_list ap;
   va_start(ap, fmt);
-  vsprintf(s, fmt, ap);
+  vsnprintf(s, sizeof(s), fmt, ap);
   va_end(ap);
 
   return AddFormData(formp, FORM_DATA, s, 0, size);