+
+ /* We now determine the length of the ASN1 string. If it differs from
+ * common_name's length, then there is a \0 before the string terminates.
+ * This can be an instance of a null-prefix attack [0].
+ *
+ * [0] https://www.blackhat.com/html/bh-usa-09/bh-usa-09-archives.html#Marlinspike
+ * */
+
+ int i=-1,j;
+ if(xname) {
+ for(;(j=X509_NAME_get_index_by_NID (xname, NID_commonName, i))!=-1;i=j);
+ }
+
+ X509_NAME_ENTRY *xentry = X509_NAME_get_entry(xname,i);
+ ASN1_STRING *sdata = X509_NAME_ENTRY_get_data(xentry);
+
+ if (strlen(common_name) != ASN1_STRING_length(sdata))
+ {
+ logprintf (LOG_NOTQUIET, _("\
+%s: certificate common name is invalid. It is possible that someone is \
+eavesdropping on you (man-in-the-middle attack)!\n"),
+ severity);
+ success = false;
+ }
+