Hardening configuration of SSL/TLS on PVA servers : CloudBlue Technical Support

Information

A CVE-2014-3566 vulnerability in SSLv3 protocol was identified by the Google security team. There is an additional whitepaper available from OpenSSL that also describes this vulnerability.

Introduction

It is necessary to keep security of HTTPS servers adequate to modern threats. Because new breaches and weaknesses in cryptographic algorithms and protocols are constantly discovered. Moreover, default settings of web servers and operating systems not always provide acceptable level of SSL/TLS security. This article aims to provide guidance about how to configure Linux and Windows web servers to provide good level of SSL/TLS security on Parallels Virtual Automation servers.

It is based on SSL/TLS Deployment Best Practices from Qualys SSLLabs.

Scope

This guide contains instructions how to configure SSL/TLS on PVA servers:

PVA Management Node
PVA Agent installed on a server hosting virtual environment

Vulnerability mitigation steps:

For Windows
For Linux

SSL/TLS Weakneses

The table below lists weaknesses which mitigations are addressed by this article.

Weakness	Mitigation
Enabled SSLv3 is a weakness because it is broken due to CVE-2014-3566(POODLE attack).	Disable SSLv3
Enabled SSLv2 is a weakness because it is broken.	Disable SSLv2
Insecure/broken algorithms used in ciphers (RC4)	Disable broken ciphers and algorithms
Small entropy ciphers (DES, 3DES) * The entropy of 128bits for keys is recommended nowadays. * 96bits entropy can be tolerable, though. * 3DES/168 has actual entropy of 112bits.	Disable or de-prioritise ciphers It is better to not disable 3DES/168bits in order to support IE on Windows XP
Anonymous key negotiation protocols (ADH)	Rare situation. Specify proper ciphers to use in Apache
CRIME vulnerability (and its successors like TIME, etc)	Disable TLS traffic compression
BEAST vulnerability	Do nothing on server side
SSL insecure renegotiation	(Apache) Check that latest update for used version of Apache is installed
FREAK vulnerability	install updates and/or disable weak ciphers

Testing SSL/TLS Security

It is not necessary that all steps described in this article be applied to all servers. Test your web servers and fix those that actually demonstrate weaknesses or vulnerabilities. The best and preferred way to assess security of SSL configuration of the web server is to use Qualys SSL Labs' test: https://www.ssllabs.com/ssltest. The mark A denote reasonably good security level. Scores lower than B require appropriate mitigation steps.

Unfortunately, SSL Labs' test cannot be applied to web servers that are not available from Internet. Use TestSSLServer tool for testing ciphers strength and CRIME vulnerability on servers in your lab (requires Java).

Basic test recommendations for "offline" testing:

Ensure certificate is up-to-date and issued by trusted authority
Ensure SSLv2 is disabled
Ensure SSLv3 is disabled too
Check RC4 cipher is not used
Check DES cipher is not used
Check CRIME is mitigated

Examples:

TestSSLServer output for Windows 2008 R2 server with default configuration. The yellow-marked text points out to insecure protocols (SSLv2 and SSLv3) and ciphers (RC4) that should be disabled. It is no longer recommended to mitigate BEAST attack on server side so we do not pay attention to respective vulnerable mark.


Supported versions: SSLv2 SSLv3 TLSv1.0
Deflate compression: no
Supported cipher suites (ORDER IS NOT SIGNIFICANT):
  SSLv2
     RC4_128_WITH_MD5
     DES_192_EDE3_CBC_WITH_MD5
  SSLv3
     RSA_WITH_RC4_128_MD5
     RSA_WITH_RC4_128_SHA
     RSA_WITH_3DES_EDE_CBC_SHA
  TLSv1.0
     RSA_WITH_RC4_128_MD5
     RSA_WITH_RC4_128_SHA
     RSA_WITH_3DES_EDE_CBC_SHA
     RSA_WITH_AES_128_CBC_SHA
     RSA_WITH_AES_256_CBC_SHA
     TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
     TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
.----------------------
Server certificate(s):
  0c6e6854baa0323d862c3e41787213e6d8e4006a: CN=10.31.104.33, O=Parallels, C=US
.----------------------
Minimal encryption strength:     strong encryption (96-bit or more)
Achievable encryption strength:  strong encryption (96-bit or more)
BEAST status: vulnerable
CRIME status: protected

Apache on CentOS 5.3 server. CRIME is not mitigated.


Supported versions: SSLv3 TLSv1.0
Deflate compression: YES
Supported cipher suites (ORDER IS NOT SIGNIFICANT):
SSLv3
    RSA_WITH_3DES_EDE_CBC_SHA
    DHE_RSA_WITH_3DES_EDE_CBC_SHA
    RSA_WITH_AES_128_CBC_SHA
    DHE_RSA_WITH_AES_128_CBC_SHA
    RSA_WITH_AES_256_CBC_SHA
    DHE_RSA_WITH_AES_256_CBC_SHA
(TLSv1.0: idem)
.---------------------
Server certificate(s):
d04135719197cefa8f601f2cf3d1ed055df41afd: CN=cp.parallelscloud.com, OU=EssentialSSL, OU=Domain Control Validated
.----------------------
Minimal encryption strength:     strong encryption (96-bit or more)
Achievable encryption strength:  strong encryption (96-bit or more)
BEAST status: vulnerable
CRIME status: vulnerable

Important note: Even if during initial deployment TestSSLServer was used it is still necessary to run ssltest when a web server become open into Internet. SSL Lab's test provides much more comprehensive checks, including server certificate strength and trustability, testing for compatibility with different browsers, more known vulnerabilities.

Windows 2008 Mitigations

Windows 2008 R2 allows broken SSLv2, SSLv3 and weak ciphers for server-side SSL/TLS connections by default.

Mitigation steps:

Upload attached disableWeakCiphers.zip file onto web server machine.
Extract the content and double click on it, and allow operating system to update registry.
Restart computer.

For more information about meanings of registry settings used, see http://support.microsoft.com/kb/245030.

Linux Mitigations

Weak Cipher and Protocols

Apply following steps, when you have encountered SSLv2, SSLv3, RC4, DES, ADH among list of supported protocols and ciphers by a server during testing.

Add (or modify) following mod_ssl options in SSL/TLS configuration of Apache web server:
```
SSLProtocol all -SSLv2 -SSLv3
SSLHonorCipherOrder on
SSLCipherSuite EECDH+AES:EDH+AES:RSA+AES:3DES:!RC4:!aNULL:!eNULL:!EXP:!MEDIUM:!LOW:!MD5
```
For PVA Management Node, the following files should be checked and updated:
- /etc/httpd/conf/httpd.conf
- /etc/httpd/conf.d/ssl.conf
- /etc/httpd/conf.d/z.pva.cc.10.conf
For a node with PVA Agent, this should be done in the following files at least:
- /etc/httpd/conf/httpd.conf
- /etc/httpd/conf.d/ssl.conf
- /etc/opt/pva/pp/plugins/httpd/include.ssl.conf
- /etc/httpd/conf.d/z.pva.pp.20.plesk.conf
- /etc/httpd/conf.d/parallels.conf
Reload Apache configuration

CRIME Vuln. Mitigation

Here is mitigation steps for CentOS 5, 6 and CloudLinux 6:

Add following variable into Apache environment (/etc/sysconfig/httpd):
```
OPENSSL_NO_DEFAULT_ZLIB=1
```
Restart Apache service