Sunday, July 27, 2014

Cyber Intelligence abusing Internet Explorer to perform Targeted Attacks

A "mandatory" step to achieve a complete and successful targeted attack is the so called: "Cyber Intelligence Phase". By definition every targeted attack owns at leeast one specific characteristic which makes it perfectly fit for a given target. As you might want agree, one of the most important activities on develping a targeted attack is to exactly know what's running on the target system. The activity which takes care of "discovering" what's running on a given system is often called Cyber Intelligence (many of you on the Cyber Intelligence field might know a little bit different definition... but this is not the point). I wont write, in this quick and dirty blog post,  about cyber intelligence, indeed I want to point you out simple techniques to perform a target enumeration by using Internet Explorer. 

One of the most used techniques to perform Cyber Intelligence through Iinternet Explorer (IE) is the "abusing of resources" (res://) calls. This techniques afflicts IE from 6. to 8. It has been widely discussed in many online sites (for example: here, here, here and here). The technique is based on the assumption that IE blocks access to local file system trhough the "file://" call, but let the "res://" call to have access to image resources on file system. To exploit this IE's behavior the attacker might look at specific executables holding (as resource)  specific images. The res abuse://  has been used as Cyber Intelligent Weapon in serveral attacks including the "waterhole campagin afffecting a Thailand NGO" as posted here. The aforementioned behavior could be exploited as follows:

From AlienVault Article
The resList contains the list of executables files used to detect AntiVirus Software. Following a simple example taken from a real case. A similar code was found into Skipot too...

From AlienVault Article
Another used technique to map software into a target host sees its implementation through the Microsoft XMLDOM ActiveX Info disclosure vulnerability. This vulnerability has been videly discussed as well (here, here, and here). Basically Microsoft.XMLDOM is an ActiveX control that can run in Internet Explorer without requiring any prompting to the user. This object contains methods that can leak information about a computer system to the operator of a website. By looking at error codes provided by the XMLDOM ActiveX control, an attacker can check for the presence of local drive letters, directory names, files, as well as internal network addresses or websites. It is confirmed that this issue affects Internet Explorer versions 6 through 11 running on Microsoft Windows through version 8.1. The following code shows an example of the implementation of such a vulnerability. It looks for the presence of specific files into the target system.

Implementation of XMLDOM ActiveX vulns
 Following on this way attackers might use more XMLDOM vulnerabilities such as CVE-2014-0322 in which Microsoft Internet Explorer 9 and 10 allows remote attackers to execute arbitrary code via vectors involving crafted JavaScript code, CMarkup, and the "onpropertychange" attribute of a script element, as exploited in the wild in January and February 2014. MSF exploits are available out there. As WebSense discussed on his Security Blog Post attackers used the described technique to identify the Microsoft EMET presence on the target system. The same technique was found into Angler Exploit Kit and later on Goon and Cool Exploit Kits too.

Cyber Intelligence, is one of the most fascinating field. It does nothing bad per se, it simply offers detailed infos to next "phases". As always happens such infos could be used by legitim systems as well as by attacker' systems. As you problably have learned in the past years... whatch out what you browse  !




Tuesday, July 1, 2014

OpenSSL CCS Attack

As you might see from my posts frequency, last months have been pretty busy to me. My hacking team and I are working really hard and we are achieving incredibly results which makes me happy but really busy as well. OpenSSL CCS Attack (CVE-2014-0224) is almost one month old and not super interesting to be exploited so far, but since we got a great experience on that specific vulnerability I decided to "fix-it" on my memories in the following way.

CVE-2014-0224 bug exists since the very first OpenSSL release and this makes (at least to me) the whole story very fascinating. The issue basically happens because OpenSSL inappropriately accepts the ChangeCipherSpec (CCS) during a handshake. The following picture shows the correct way to implement a full protocol handshake.

The bug finds its own start if If a ChangeCipherSpec message is injected after the ServerHello but before the master secret has been generated  (ClientKeyExchange). At this point ssl3_do_change_cipher_spec generates the keys pair and the expected Finished hash for the handshake with an empty master secret (implementation bug). Moreover, the keys pair will be latched because further ChangeCipherSpec messages regenerate the expected Finished hash, but not new keys anymore. The following image shows the injection time frame.



The buggy code is the following one (the red numbers follow the above description):

int ssl3_do_change_cipher_spec(SSL *s)
 {
 int i;
 const char *sender;
 int slen;

 if (s->state & SSL_ST_ACCEPT)
  i=SSL3_CHANGE_CIPHER_SERVER_READ;
 else
  i=SSL3_CHANGE_CIPHER_CLIENT_READ;

 if (s->s3->tmp.key_block == NULL)1
  {
  if (s->session == NULL)
   {
   /* might happen if dtls1_read_bytes() calls this */
         SSLerr(SSL_F_SSL3_DO_CHANGE_CIPHER_SPEC,SSL_R_CCS_RECEIVED_EARLY);
   return (0);
   }

  s->session->cipher=s->s3->tmp.new_cipher;
  if (!s->method->ssl3_enc->setup_key_block(s)) return(0); 2
  }

 if (!s->method->ssl3_enc->change_cipher_state(s,i))
  return(0);

 /* we have to record the message digest at
  * this point so we can get it before we read
  * the finished message */
 if (s->state & SSL_ST_CONNECT)
  {
  sender=s->method->ssl3_enc->server_finished_label;
  slen=s->method->ssl3_enc->server_finished_label_len;
  }
 else
  {
  sender=s->method->ssl3_enc->client_finished_label;
  slen=s->method->ssl3_enc->client_finished_label_len;
  }

 i = s->method->ssl3_enc->final_finish_mac(s,
  sender,slen,s->s3->tmp.peer_finish_md); 3
 if (i == 0)
  {
  SSLerr(SSL_F_SSL3_DO_CHANGE_CIPHER_SPEC, ERR_R_INTERNAL_ERROR);
  return 0;
  }
 s->s3->tmp.peer_finish_md_len = i;

 return(1);
 }

Fortunately a patch is available here and a simple go tool to check the bug presence is here. For having more detailed infos, please visit (this post, and the original post).