+ else
+ {
+ /* 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.
+ *
+ * https://www.blackhat.com/html/bh-usa-09/bh-usa-09-archives.html#Marlinspike
+ * */
+
+ int i = -1, j;
+ X509_NAME_ENTRY *xentry;
+ ASN1_STRING *sdata;
+
+ if (xname) {
+ for (;;)
+ {
+ j = X509_NAME_get_index_by_NID (xname, NID_commonName, i);
+ if (j == -1) break;
+ i = j;
+ }
+ }
+
+ xentry = X509_NAME_get_entry(xname,i);
+ sdata = X509_NAME_ENTRY_get_data(xentry);
+ if (strlen (common_name) != ASN1_STRING_length (sdata))
+ {
+ logprintf (LOG_NOTQUIET, _("\
+%s: certificate common name is invalid (contains a NUL character).\n\
+This may be an indication that the host is not who it claims to be\n\
+(that is, it is not the real %s).\n"),
+ severity, quote (host));
+ success = false;
+ }
+ }
+