Bug 1335921

Summary:	openssl: Disable TLS connections with less than 1024-bit DH parameters
Product:	Red Hat Enterprise Linux 6	Reporter:	Nikos Mavrogiannopoulos <nmavrogi>
Component:	openssl	Assignee:	Tomas Mraz <tmraz>
Status:	CLOSED ERRATA	QA Contact:	Stanislav Zidek <szidek>
Severity:	unspecified	Docs Contact:	Mirek Jahoda <mjahoda>
Priority:	unspecified
Version:	6.9	CC:	kengert, nss-nspr-maint, qe-baseos-security, szidek, tmraz
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	openssl-1.0.1e-51.el6	Doc Type:	Deprecated Functionality
Doc Text:	OpenSSL clients using TLS with less than 1024-bit DH are not allowed This change prevents OpenSSL clients from connecting to servers with Diffie-Hellman (DH) parameters less than 1024 bits. This ensures that allowed clients using OpenSSL 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:	1335920	Environment:
Last Closed:	2017-03-21 10:11:35 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 14:28:23 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 2 Tomas Mraz 2016-10-05 09:21:55 UTC

The system administrator can reenable shorter DH support with:

echo 'MinimumDHBits 768' >> /etc/pki/tls/legacy-settings

Any value between 512 and 10000 is supported so this can be used to even raise the minimum to 2048 if needed by the system administrator.

Comment 11 errata-xmlrpc 2017-03-21 10:11:35 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/RHBA-2017-0660.html