--- snmplib/scapi.c	2008-06-06 15:44:30 +0000
+++ snmplib/scapi.c	2008-06-06 15:47:16 +0000
@@ -563,6 +563,10 @@
     }
 
 
+    if (maclen != USM_MD5_AND_SHA_AUTH_LEN) {
+        QUITFUN(SNMPERR_GENERR, sc_check_keyed_hash_quit);
+    }
+
     /*
      * Generate a full hash of the message, then compare
      * the result with the given MAC which may shorter than