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Details about how MD5 weaknesses especially what is refered to as known prefix collisions were used to help to compromise the trust put into one of the CA's that is builtin major browsers :
http://www.win.tue.nl/hashclash/rogue-ca/

Quick Summary:
Not all CAs using MD5 are automaticaly broken, three things were required :
- MD5 signed CA
- prediction of the Serial Number (RapidSSL increments by one)
- prediction of the certificate validity date (RapidSSL issues always 6 second after your press the button.
- A way to find collisions fast enough

Only with these 4 things in place it was possible to pull this off.

More information :

History:
2004 - first attacks against md5
2006 - Colliding PKCS Certificates http://www.win.tue.nl/~bdeweger/CollidingCertificates/
2007 - know prefix collision attacks against md5 futher speeding up the time it takes to find collisions.

Basicaly the stage for the attack shown this year at 25c3 attack was already set in 2006 however the Serial number + Validity period were a problem, because you don't know where they are (in the data) in advance.

So how to reduce the entropy (uncertainty what the validty of the certficate is) ? They found a way to use the RAPIDSSL autonomous system which gives the certificate extactly 6 seconds after you click the I approve button.

What about the Serial number? How to predict the serial number ? RapidSSL just incremented the serial number by one...

This means they potentialy could predict the serial number,however they need three days to bruteforce the collisions - so they needed to get the serial number right for that date - they choose sunday night because the entropy introduced by customer buying certificates hindered the process of hitting the sweet spot.

The required 4 attempts, the three previous times someone else got the Serial Number they targeted.

The question what happens with certificates that use MD5 checksums have been
openly asked (and tried to be answered) in 2005 as shown here :
http://www.cryptography.com/cnews/hash.html

Summary :
Academic research + hacker ingeniousty at it's finest. We need more of it. Awesome.
This only worked because RapidSSL incremented the serial number by 1 and they could predict the validity date.

So, in other words : Remove (or edit the Trustsettings) for the following CA's -

Firefox :
* RapidSSL
C=US, O=Equifax Secure Inc., CN=Equifax Secure Global eBusiness CA-1
* FreeSSL (free trial certificates offered by RapidSSL)
C=US, ST=UT, L=Salt Lake City, O=The USERTRUST Network, OU=http://www.usertrust.com, CN=UTN-USERFirst-Network Applications
* TC TrustCenter AG
C=DE, ST=Hamburg, L=Hamburg, O=TC TrustCenter for Security in Data Networks GmbH, OU=TC TrustCenter Class 3 CA/emailAddress=certificate@trustcenter.de
* RSA Data Security
C=US, O=RSA Data Security, Inc., OU=Secure Server Certification Authority
* Thawte
C=ZA, ST=Western Cape, L=Cape Town, O=Thawte Consulting cc, OU=Certification Services Division, CN=Thawte Premium Server CA/emailAddress=premium-server@thawte.com
* verisign.co.jp
O=VeriSign Trust Network, OU=VeriSign, Inc., OU=VeriSign International Server CA - Class 3, OU=www.verisign.com/CPS Incorp.by Ref. LIABILITY LTD.(c)97 VeriSign


(Thanks to Security4all)

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Relates to this story :
http://www.pcworld.com/article/155190/new_web_attack_exploits_unpatched_ie_flaw.html

Here is the extracted shellcode from the IE7 0day referenced above.
XOR encoded payload for analysis - compile and run it through Ollydbg.
http://secdev.zoller.lu/research/shellcode_ana1.c

The decrypted shellcode is available for download here :
http://secdev.zoller.lu/research/decrypted_asm_shellcode.txt

Update
I was not interested in posting the 0day, but somebody choose to do so on milw0rm.com, so I might aswell link there : http://milw0rm.com/sploits/2008-iesploit.tar.gz

Update2
HDmoore posted a nice analysis here : http://www.breakingpointsystems.com/community/

Update 3
11/12/2008 - 04:19
5 out of 32 scanners recognising the 0day in HTML form
http://www.virustotal.com/de/analisis/596d88d57bc91d977f037f317eb9aa99

11/12/2008 - 17:34
7 out of 38 scanners recognising the exploit
http://www.virustotal.com/en/analisis/a68e1c2813483a58cfdd6509ccd8fe5e
http://virscan.org/report/4907067f0f0aab53261348413dea9bc9.html

12/12/2008 - 17:04
11 out of 38 scanners recognising the exploit
http://www.virustotal.com/de/analisis/475269215b8379537e45a8fd94f8dc9c
http://virscan.org/report/7a00119178654949124b62e85d2a42c8.html

13/12/2008 - 17:00
12 out of 38 AV engines recognise the exploit
http://www.virustotal.com/en/analisis/286266a9e8096ef17bb1aa6f15a1a31f

14/12/2008 - 19:45
14 out of 38 AV engines recognise the exploit
http://www.virustotal.com/en/analisis/5e8909eea79dc716caac8af09f22ac3f
http://virscan.org/report/47f8b4811744eaebb7d48fcc942009cb.html


15/12/2008 - 18:25
Still 14 out of 38 AV engines recognise the exploit
http://www.virustotal.com/de/analisis/592728a9493349692fc2b33e799a6a33

16/12/2008 - 18:25
15 out of 38 AV engines recognise the exploit
http://www.virustotal.com/en/analisis/28208f37d1d2c732be026a9a2990c86e

17/12/2008 - 18:25
Still at 15 out of 38 AV engines recognise the exploit
http://www.virustotal.com/de/analisis/2fa1f88d9a1372f023844af40911c83e

19/12/2008 - 16:04
18 out of 38 AV engines recognise the exploit
http://www.virustotal.com/de/analisis/2d23479870f34a8786f3229da5db23cf

20/12/2008 - 16:04
19 out of 38 AV engines recognise the exploit
http://www.virustotal.com/de/analisis/6f21e0dffcc117b695324ed93cd7a803

21/12/2008 - 16:04
20 out of 38 AV engines recognise the exploit
http://www.virustotal.com/en/analisis/6dd28dced88f1c8982503e8547d5ef01

22/12/2008 - 16:04
21 out of 38 AV engines recognise the exploit
http://www.virustotal.com/en/analisis/37537b52f8d4584fb1d294f3ccc0b385

23/12/2008 - 16:04
21 out of 38 AV engines recognise the exploit
http://www.virustotal.com/de/analisis/e22efb9c30a1e7e911466b0194d2f279

24/12/2008 - 16:04
22 out of 38 AV engines recognise the exploit

http://www.virustotal.com/de/analisis/9ee7bf2ca2aa85b6de52a08d1e417a15


26/12/2008 - 16:04
22 out of 38 AV engines recognise the exploit (Result misses Securecomputing)
http://www.virustotal.com/de/analisis/40439a3a049d46623cfffd7e2ed05c92

27/12/2008 - 16:04
22 out of 38 AV engines - (Result misses VBA32)
http://www.virustotal.com/de/analisis/5a8e26b11632745dc8c5742d5403b8ec

28/12/2008 - 16:04
22 out of 38 AV engines - (Result misses VBA32)
http://www.virustotal.com/de/analisis/89fdc7975178090411d72b167e4420e8

30/12/2008
21 out of 38 AV engines - (CA) E-trust no longer recognises the sample, Esafe missing
http://www.virustotal.com/de/analisis/a6e158b4cdca3da09480fdd4c49e5934