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Category:   Application (VPN)  >   OpenSSL Vendors:   OpenSSL.org
OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
SecurityTracker Alert ID:  1032476
SecurityTracker URL:  http://securitytracker.com/id/1032476
CVE Reference:   CVE-2015-4000   (Links to External Site)
Updated:  Jun 11 2015
Original Entry Date:  Jun 3 2015
Impact:   Modification of authentication information
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  

Description:   A vulnerability was reported in OpenSSL. A remote user may be able to decrypt TLS connections in certain situations.

A remote user that can conduct a man-in-the-middle attack can cause the target system to downgrade the Diffie-Hellman algorithm to 512-bit export-grade cryptography. The remote user may then be able to decrypt the connection.

This vulnerability resides in the TLS protocol and not in the specific TLS implementation, but the vulnerability is exposed because the target system supports export-grade ciphers.

This attack is known as the "Logjam" attack.

The original advisory is available at:

https://weakdh.org/imperfect-forward-secrecy.pdf

David Adrian, Karthikeyan Bhargavan, Zakir Durumeric, Pierrick Gaudry, Matthew Green, J. Alex Halderman, Nadia Heninger, Drew Springall, Emmanuel Thome, Luke Valenta, Benjamin VanderSloot, Eric Wustrow, Santiago Zanella-Beguelin, and Paul Zimmermann reported this vulnerability.

Impact:   A remote user that can conduct a man-in-the-middle attack can cause the target system to use weak cryptography that can be decrypted.
Solution:   The vendor has issued a fix (1.0.1n, 1.0.2b).

The vendor's advisories are available at:

https://www.openssl.org/blog/blog/2015/05/20/logjam-freak-upcoming-changes/
https://www.openssl.org/news/secadv_20150611.txt

Vendor URL:  www.openssl.org/news/secadv_20150611.txt (Links to External Site)
Cause:   Authentication error
Underlying OS:  Linux (Any), UNIX (Any), Windows (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Jun 4 2015 (Red Hat Issues Fix) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
Red Hat has issued a fix for Red Hat Enterprise Linux 6 and 7.
Jun 5 2015 (CentOS Issues Fix) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
CentOS has issued a fix for CentOS 6.
Jun 5 2015 (CentOS Issues Fix) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
CentOS has issued a fix for CentOS 7.
Jun 12 2015 (FreeBSD Issues Fix) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
FreeBSD has issued a fix for FreeBSD 8.4, 9.3, and 10.1.
Jun 30 2015 (Red Hat Issues Fix) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
Red Hat has issued a fix for Red Hat Enterprise Linux 5.
Aug 11 2015 (HP Issues Fix for HP-UX) OpenSSL TLS Diffie-Hellman Export Cipher Downgrade Attack Lets Remote Users Decrypt Connections
HP has issued a fix for HP-UX 11.31.



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