Bug 1335924

Summary: gnutls: Disable TLS connections with less than 1024-bit DH parameters
Product: Red Hat Enterprise Linux 6 Reporter: Nikos Mavrogiannopoulos <nmavrogi>
Component: gnutlsAssignee: Nikos Mavrogiannopoulos <nmavrogi>
Status: CLOSED ERRATA QA Contact: Hubert Kario <hkario>
Severity: unspecified Docs Contact: Mirek Jahoda <mjahoda>
Priority: unspecified    
Version: 6.9CC: hkario, nmavrogi, qe-baseos-security, szidek, tmraz
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: gnutls-2.12.23-3.el6 Doc Type: Deprecated Functionality
Doc Text:
*GnuTLS* clients with less than 1024-bit DH are not allowed This change prevents GNU Transport Layer Security (GnuTLS) clients from connecting to servers with Diffie-Hellman (DH) parameters less than 1024 bits. This ensures that allowed clients using *GnuTLS* are not vulnerable to attacks such as the LOGJAM attack. A system administrator can enable shorter DH parameter support by modifying the "MinimumDHBits" option in the `/etc/pki/tls/legacy-settings`, for example: echo 'MinimumDHBits 768' > /etc/pki/tls/legacy-settings This option can be used to additionally raise the minimum if required by the system administrator.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2017-03-21 09:04:03 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1335911, 1343211    

Description Nikos Mavrogiannopoulos 2016-05-13 14:31:15 UTC 
RHEL includes several cryptographic components who's security doesn't remain constant over time. Algorithms such as (cryptographic) hashing and encryption typically have a lifetime after which they are considered either too risky to use or plain insecure. That would mean we need to phase out such algorithms from the default settings, or completely disable if they could cause irreparable issue. 

This bug is about disabling any TLS connections which utilize less than 1024-bit Diffie-Hellman parameters, while at the same hand providing a configuration method for these parameters to be allowed when needed.

For future extensibility in RHEL-7 it is recommended for any introduced configuration method to be re-usable for future algorithm or parameter deprecation (e.g., SHA1 or less than 1024-bit RSA/DH parameters), and ideally part of upstream.
Comment 9 errata-xmlrpc 2017-03-21 09:04:03 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2017-0574.html