Internet Explorer SSL Vulnerability :: essays research papers

Abstract Internet Explorer's implementation of SSL contains a vulnerability that allows for an active, undetected, man in the middle attack. No dialogs are shown, no warnings are given. ======================================================================== Description In the normal case, the administrator of a web site might wish to provide secure communication via SSL. To do so, the administrator generates a certificate and has it signed by a Certificate Authority. The generated certificate should list the URL of the secure web site in the Common Name field of the Distinguished Name section. The CA verifies that the administrator legitimately owns the URL in the CN field, signs the certificate, and gives it back. Assuming the administrator is trying to secure www.thoughtcrime.org, we now have the following certificate structure: [CERT - Issuer: VeriSign / Subject: VeriSign] -> [CERT - Issuer: VeriSign / Subject: www.thoughtcrime.org] When a web browser receives this, it should verify that the CN field matches the domain it just connected to, and that it's signed using a known CA certificate. No man in the middle attack is possible because it should not be possible to substitute a certificate with a valid CN and a valid signature. However, there is a slightly more complicated scenario. Sometimes it is convenient to delegate signing authority to more localized authorities. In this case, the administrator of www.thoughtcrime.org would get a chain of certificates from the localized authority: [Issuer: VeriSign / Subject: VeriSign] -> [Issuer: VeriSign / Subject: Intermediate CA] -> [Issuer: Intermediate CA / Subject: www.thoughtcrime.org] When a web browser receives this, it should verify that the CN field of the leaf certificate matches the domain it just connected to, that it's signed by the intermediate CA, and that the intermediate CA is signed by a known CA certificate. Finally, the web browser should also check that all intermediate certificates have valid CA Basic Constraints. You guessed it, Internet Explorer does not check the Basic Constraints. ========================================================================== Exploit So what does this mean? This means that as far as IE is concerned, anyone with a valid CA-signed certificate for ANY domain can generate a valid CA-signed certificate for ANY OTHER domain. As the unscrupulous administrator of www.thoughtcrime.org, I can generate a valid certificate and request a signature from VeriSign: [CERT - Issuer: VeriSign / Subject: VeriSign] -> [CERT - Issuer: VeriSign / Subject: www.thoughtcrime.org] Then I generate a certificate for any domain I want, and sign it using my run-of-the-mill joe-blow CA-signed certificate: [CERT - Issuer: VeriSign / Subject: VeriSign] -> [CERT - Issuer: VeriSign / Subject: www.thoughtcrime.org] -> [CERT - Issuer: www.thoughtcrime.org / Subject: www.amazon.com] Since IE doesn't check the Basic Constraints on the www.thoughtcrime.org certificate, it accepts this certificate chain as valid for www.amazon.com. Anyone with any CA-signed certificate (and the corresponding private