** 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.
+
+ The source code we analysis was from ubuntu: apt-get source <package
name>.And we use this command in Ubuntu 12.04.
+ 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 dma, the following is details:
-----------------------------------------------------------------------------
file : dma/dma-0.0.2010.06.17/crypto.c
-----------------------------------------------------------------------------
function : smtp_init_crypto
-----------------------------------------------------------------------------
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 dma is not
- secure. For instance, missing hostname or expired time check when
- verifying x509 certificate.
+ 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.
At first, we should configure the software environment:
1. configure the file /etc/dma/dma.conf:
# $DragonFly: src/etc/dma/dma.conf,v 1.2 2008/02/04 10:11:41 matthias Exp $
#
# Your smarthost (also called relayhost). Leave blank if you don't want
# smarthost support.
# NOTE: on Debian systems this is handled via debconf!
# Please use dpkg-reconfigure dma to change this value.
#SMARTHOST
SMARTHOST smtp.gmail.com
# Use this SMTP port. Most users will be fine with the default (25)
#PORT 25
PORT 587
# Path to your alias file. Just stay with the default.
#ALIASES /etc/aliases
# Path to your spooldir. Just stay with the default.
#SPOOLDIR /var/spool/dma
# SMTP authentication
AUTHPATH /etc/dma/auth.conf
# Uncomment if yout want TLS/SSL support
SECURETRANSFER
# Uncomment if you want STARTTLS support (only used in combination with
# SECURETRANSFER)
STARTTLS
# Uncomment if you have specified STARTTLS above and it should be allowed
# to fail ("opportunistic TLS", use an encrypted connection when available
# but allow an unencrypted one to servers that do not support it)
#OPPORTUNISTIC_TLS
# Path to your local SSL certificate
#CERTFILE
# If you want to use plain text SMTP login without using encryption, change
# the SECURE entry below to INSECURE. Otherwise plain login will only work
# over a secure connection. Use this option with caution.
INSECURE
# Uncomment if you want to defer your mails. This is useful if you are
# behind a dialup line. You have to submit your mails manually with dma -q
#DEFER
# Uncomment if you want the bounce message to include the complete original
# message, not just the headers.
#FULLBOUNCE
# The internet hostname dma uses to identify the host.
# If not set or empty, the result of gethostname(2) is used.
# If MAILNAME is an absolute path to a file, the first line of this file
# will be used as the hostname.
# NOTE: on Debian systems this is handled via debconf!
# Please use dpkg-reconfigure dma to change this value.
MAILNAME /etc/mailname
# Masquerade envelope from addresses with this address/hostname.
# Use this if mails are not accepted by destination mail servers because
# your sender domain is invalid.
# By default, MASQUERADE is not set.
# Format: MASQUERADE [user@][host]
# Examples:
# MASQUERADE john@ on host "hamlet" will send all mails as john@hamlet
# MASQUERADE percolator will send mails as $username@percolator, e.g.
fish@percolator
# MASQUERADE herb@ert will send all mails as herb@ert
2. configure the file /etc/dma/auth.conf:
# $DragonFly: src/etc/dma/auth.conf,v 1.1 2008/02/02 18:24:00 matthias Exp $
#
# SMTP authentication entries (currently AUTH LOGIN only)
# Format: user|my.smarthost.example.com:password
[email protected]|smtp.gmail.com:Password
3. configure ~/.muttrc：
set sendmail="/usr/sbin/dma -f [email protected]"
set folder="~/Mail"
set mbox="~/Mail/inbox"
#set mbox_type=maildir
set spoolfile="~/Mail/inbox"
set postponed="~/Mail/postponed"
set record="~/Mail/sent"
my_hdr From: [email protected]
Ok ,let's start!
- 一.Hostname verification
- 1. change /etc/hosts in order to simulate the DNS hijack
- 182.254.3.179 smtp.gmail.com
- （182.254.3.179 is a normal smtp server）
-
- 2. use mutt to send the mail ( mutt use dma as a MTA)
-
- 3. result : receivethe mail !
-
- The fetch succeeded, indicating the software didn't check the hostname
- against the signee of the certificate.
-
- 二. Also for expired time check,
+ for expired time check,
1. change the system time to 2200 to guarantee the certificate to be expired.
2. run mutt to send email
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/1380458
Title:
dma have some SSL security problems
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