[Bug 1376592] Re: X509 certificate verification problem

[rainkin]

** Information type changed from Public to Public Security

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https://bugs.launchpad.net/bugs/1376592

Title:
  X509 certificate verification problem

Status in “freetds” package in Ubuntu:
  New

Bug description:
  Hostname verification is an important step when verifying X509
  certificates, however, people tend to miss the step or to
  misunderstand the APIs when using SSL/TLS, which might cause severe
  man in the middle attack and break the entire TLS mechanism.

  We believe that freetds-bin didn't check whether the hostname matches
  the name in the SSL certificate and the expired date of the
  certificate.

  We found the vulnerability by static analysis, typically, a process of
  verification involves calling a chain of API, and we can deduce
  whether the communication process is vulnerable by detecting whether
  the function call process matches a certain model. For example, when
  using OPENSSL, if we call SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_NONE,
  null), we should verify the certificate by calling the function
  SSL_get_peer_certificate() to get the certificate. If the source code
  does not match this model, then we can deduce this code is vulnerable.
  What’ more , Gnutls is the same as Openssl.

  To verify the result:

  一.Hostname verification:
  1. configure the file freetds.conf :
         # A typical Microsoft server
  [sqlserver2000]
          host = hackbyfun.sqlserver.com
          port = 1433
          tds version = 8.0
          encrpytion = require
  2.wirte the file /etc/hosts in order to simulate DNS hijack:
    10.214.146.123     hackbyfun.sqlserver.com
   (PS: 10.214.146.123 is a normal sql server ip, its domain name is safe.sqlserver.com )

  3.connect with freetds-bin
  tsql -S sqlserver2000 -U sa -P <your password>

  4.result：connect succeed!!

  The fetch succeeded, indicating freetds-bin didn't check the hostname
  against the signee of the certificate.

  二. Also for expired time check,
  1. change the system time to 2200 to guarantee the certificate to be expired.
  2. the same as the above process. Run freetds-bin to connect a normal sql server
  3. result :connect succeed!!

  The fetch succeeded again and no warning was given, indicating
  freetds-bin didn't check whether the certificate expired or not.

  (PS: I have saved the wireshark packages, and upload these files)

  I am running freetds-bin 9.1-5 in ubuntu 14.04 LTS.

  for more information about the importance of checking hostname:
  see http://people.stfx.ca/x2011/x2011ucj/SSL/p38-georgiev.pdf

  Thanks.

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