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Category:   OS (Microsoft)  >   Windows Schannel Vendors:   Microsoft
Windows Schannel TLS Export Cipher Bug Lets Remote Users Downgrade Session Security
SecurityTracker Alert ID:  1031833
SecurityTracker URL:
CVE Reference:   CVE-2015-1637   (Links to External Site)
Updated:  Mar 10 2015
Original Entry Date:  Mar 5 2015
Impact:   Disclosure of authentication information, Disclosure of system information, Disclosure of user information, Modification of system information, Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 2003 SP2, Vista SP2, 2008 SP2, 7 SP1, 2008 R2 SP1, 8, 8.1, 2012, 2012 R2, RT, RT 8.1; and prior service packs
Description:   A vulnerability was reported in Windows Schannel. A remote user can downgrade the TLS session security and potentially recover keys.

A remote user that can conduct a man-in-the-middle attack can force a downgrade to an export-grade cipher suite and then conduct a key factoring attack to recover the target server's RSA private key. The remote user can then determine the TLS master key for that session.

[Editor's note: This is known as a "FREAK" attack.]

The original advisory is available at:

The miTLS Team reported this vulnerability.

Impact:   A remote user can downgrade the session security and then conduct a key factoring attack to recover the target server's export-grade RSA private key and to obtain the TLS master key for that session.
Solution:   The vendor has issued a fix.

The vendor's advisories are available at:

Vendor URL: (Links to External Site)
Cause:   State error

Message History:   None.

 Source Message Contents

[Original Message Not Available for Viewing]

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