** Description changed:
- Recently, we are trying to find SSL security problems by static
- analysis. For example, as we all know, 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. And static analysis is a way of finding whether the APIs are
- called correctly.
+ Recently, our group is trying to find SSL security problems by static
+ analysis. When using Openssl, 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. And static
+ analysis is a way of finding whether the APIs are called correctly.
+
+ Now we just check whether a software verify the certitiface chain when
+ using Openssl.
+
+ 一. How we ensure whether a software check the certificate chain or not?
+ We make a matching algorithm. If source code doesn't match this, the software
is not secure.
+
+ Typically, when Openssl clients want to verify a certificate, there are
+ the following choices:
+
+ 1. Using built-in certificate verification(chain of trust verification,
expired validation, etc)
+ [Example 1]
+ /**
+ * set VERIFY_PEER flag before the establishment of a SSL connection
+ * OPENSSL will drop connection during handshake if verification fails
+ * No custom callback function used.
+ */
+ SSL_CTX_set_verify(ctx,VERIFY_PEER,NULL);
+
+ [Example 2]
+
+ //check the built-in verification result after the SSL handshake
+
+ if(SSL_get_peer_certificate(ssl)!=NULL &&
SSL_get_verify_result(ssl)==X509_V_OK)
+ {
+ //PASS
+ }
+ else
+ {
+ //FAIL
+ }
+
+ 2. Using custom verification.
+
+ [Example 3]
+ X509* usrcert = SSL_get_peer_certificate(ssl);
+ rootCertStore = X509_STORE_new();
+ .. ..
+ ctx = X509_STORE_CTX_new();
+ ret = X509_STORE_CTX_init(ctx,rootCertStore,usrCert,NULL);
+ ret = X509_verify_cert(ctx)
+
+ This example read the certificate out using SSL_get_peer_certificate
+ API. Then it use X509 API suite to do certificate verification. X509 API
+ is part of OPENSSL library. Theoretically, a developer can use any API
+ in any libraries to do this verification, but in practice, we only
+ identify the case above: using X509 API suite.
+
+ 3. Add restrictions or relaxations to built-in certificate verification
+
+ The built-in certificate verification in OPENSSL library can be extended by
using custom callback functions. By default, this callback option is NULL,
indicating completely use built-in verification.
+ By adding this callback function, the developer can decide if they accept the
verify result by openssl, and they can modify the result whenever they what.
+
+ [Example 4]
+ SSL_CTX_set_verify(ctx,VERIFY_PEER,mycallback);
+ static mycallback(int preverify_ok, X509_STORE_CTX *ctx)
+ {
+ ....
+ ....
+ return preverify_ok;
+ }
+
+ 二. The analysis result
Now, we find some SSL problems in epic5, the following is details:
-----------------------------------------------------------------------------
file : epic5/epic5-1.1.2/source/ssl.c
-----------------------------------------------------------------------------
function : ssl_connect
-----------------------------------------------------------------------------
SSL method : \
-----------------------------------------------------------------------------
call SSL_CTX_set_verify() : NOT FOUND
-----------------------------------------------------------------------------
Have SSL_CTX_set_verify ( SSL_set_verify) callback : NO
-----------------------------------------------------------------------------
call SSL_get_peer_certificate(): YES (but NO X509 suite API for custom
verification)
-----------------------------------------------------------------------------
call SSL_get_verify_result(): NO
-----------------------------------------------------------------------------
According to the above result, we think the SSL connection in epic5 is
not secure.
- More specifically , we can take function SSL_CTX_set_verify() 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 at first.
- Then use X509 APIs or self-define function to verify the certificate we
- get. If the source code does not match this model, then we can deduce
- this code is vulnerable. And other APIs have similar problems.
+ 三. How we prove the result we got.
To verify the result we make, we attack the software manually.
- 一.Hostname verification
- 1. change /etc/hosts in order to simulate the DNS hijack
- 46.137.23.30 attacker.com
- （46.137.23.30 is a normal irc server）
-
- 2. #rainkin@rainkin:~$ epic5 rainkin attacker.com:6697:::OPN:irc-ssl
-
- 3. result : succeed!!!
-
- The fetch succeeded, indicating the software 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.
+ 1. change the system time to 2200 to guarantee the certificate to be
+ expired.
2. run epic5 to connect to a normal irc server.
3. result:succeed!!
The fetch succeeded again and no warning was given, indicating the
software didn't check whether the certificate expired or not.
PS: I have saved the SSL connection Wireshark packages, and upload these
files.
for more information, you can see the paper:
http://people.stfx.ca/x2011/x2011ucj/SSL/p38-georgiev.pdf
and more details you can contact with us, we will be very glad for your
responce.
Thanks.
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https://bugs.launchpad.net/bugs/1380435
Title:
epic5's SSL connection is not secure
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