Detect NULs in common name.

[wget] / src / openssl.c

diff --git a/src/openssl.c b/src/openssl.c
index f5239ede6e8f0b478a81625261a805165e13403c..dd3a62a4ee0cf594f97cc35655be548e259dd3c4 100644 (file)
--- a/src/openssl.c
+++ b/src/openssl.c
@@ -390,7 +390,7 @@ static struct transport_implementation openssl_transport = {
    Returns true on success, false on failure.  */
 
 bool
    Returns true on success, false on failure.  */
 
 bool

-ssl_connect (int fd) 
+ssl_connect_wget (int fd) 

 {
   SSL *conn;
   struct openssl_transport_context *ctx;
 {
   SSL *conn;
   struct openssl_transport_context *ctx;


@@ -473,7 +473,7 @@ pattern_match (const char *pattern, const char *string)
    its certificate, corresponds to HOST.  (HOST typically comes from
    the URL and is what the user thinks he's connecting to.)
 
    its certificate, corresponds to HOST.  (HOST typically comes from
    the URL and is what the user thinks he's connecting to.)
 

-   This assumes that ssl_connect has successfully finished, i.e. that
+   This assumes that ssl_connect_wget has successfully finished, i.e. that

    the SSL handshake has been performed and that FD is connected to an
    SSL handle.
 
    the SSL handshake has been performed and that FD is connected to an
    SSL handle.
 


@@ -569,9 +569,35 @@ ssl_check_certificate (int fd, const char *host)
      - Ensure that ASN1 strings from the certificate are encoded as
        UTF-8 which can be meaningfully compared to HOST.  */
 
      - Ensure that ASN1 strings from the certificate are encoded as
        UTF-8 which can be meaningfully compared to HOST.  */
 

+  X509_NAME *xname = X509_get_subject_name(cert);

   common_name[0] = '\0';
   common_name[0] = '\0';

-  X509_NAME_get_text_by_NID (X509_get_subject_name (cert),
+  X509_NAME_get_text_by_NID (xname,

                              NID_commonName, common_name, sizeof (common_name));
                              NID_commonName, common_name, sizeof (common_name));

+
+  /* 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;
+    }
+

   if (!pattern_match (common_name, host))
     {
       logprintf (LOG_NOTQUIET, _("\
   if (!pattern_match (common_name, host))
     {
       logprintf (LOG_NOTQUIET, _("\