http://net-snmp.git.sourceforge.net/git/gitweb.cgi?p=net-snmp/net-snmp;a=commit;h=4c5633f1603e4bd03ed05c37d782ec8911759c47

--- agent/mibgroup/agent/extend.c	2008-05-29 09:59:06.000000000 +0000
+++ agent/mibgroup/agent/extend.c.oden	2012-06-21 10:15:46.000000000 +0000
@@ -1124,7 +1124,7 @@ _extend_find_entry( netsnmp_request_info
              * ...and check the line requested is valid
              */
             line_idx = *table_info->indexes->next_variable->val.integer;
-            if (eptr->numlines < line_idx)
+            if (line_idx < 1 || line_idx > eptr->numlines)
                 return NULL;
         }
         return eptr;
@@ -1297,6 +1297,10 @@ handle_nsExtendOutput2Table(netsnmp_mib_
                  * Determine which line we've been asked for....
                  */
                 line_idx = *table_info->indexes->next_variable->val.integer;
+                if (line_idx < 1 || line_idx > extension->numlines) {
+                    netsnmp_set_request_error(reqinfo, request, SNMP_NOSUCHINSTANCE);
+                    continue;
+                }
                 cp  = extension->lines[line_idx-1];
 
                 /*