Full Report
Transport layer security has had a rough ride recently, with a number of vulnerabilities being reported. At a time when trust is required between you and the site you are interacting with, it’s key that website owners configure their sites to be as secure as possible. With that in mind, I decided to analyse HTTP Security Headers from the top 10k Alexa websites, and look at what SSL Ciphers were being used on those websites.
Analysis Summary
Based on the context provided, which discusses poor SSL cipher choice among top websites, the following best practices focus heavily on securing Transport Layer Security (TLS/SSL) configurations.
# Best Practices: Secure TLS/SSL Cipher Suite Configuration
## Overview
These practices address the critical need to secure communication channels (HTTP/S) by ensuring that only strong, modern, and secure cryptographic algorithms (cipher suites) are used by web servers, mitigating risks associated with known vulnerabilities in older or weak ciphers.
## Key Recommendations
### Immediate Actions
1. **Disable SSLv2 and SSLv3 Protocols:** Immediately configure the web server to completely disable the use of SSL version 2.0 and SSL version 3.0 protocols, as they are fundamentally insecure.
2. **Remove Weak Cipher Suites:** Audit and immediately remove the lowest-strength cipher suites (e.g., those using RC4, 3DES, or low bit-length RSA key exchange/ciphers) from the server's accepted list.
3. **Verify Current Protocol Support:** Confirm that the server is configured to exclusively use TLS 1.2 and, where supported by clients, TLS 1.3.
### Short-term Improvements (1-3 months)
1. **Prioritize Modern Cipher Suites:** Enforce a server configuration that prioritizes Forward Secrecy (using Ephemeral Diffie-Hellman – DHE or ECDHE) combined with strong encryption algorithms (e.g., AES-256 GCM or ChaCha20-Poly1305).
2. **Implement Cipher String Ordering:** Explicitly define the server's preferred order of accepted cipher suites, putting the strongest and fastest supported ciphers at the top of the list, ensuring the client prefers them.
3. **Regular Vulnerability Scanning:** Implement quarterly scans using tools like `sslscan` or commercial vulnerability scanners against port 443 to proactively detect the presence of weak ciphers or outdated protocols.
### Long-term Strategy (3+ months)
1. **Mandate TLS 1.3 Readiness:** Plan the full deprecation of TLS 1.2 support within the next year, assuming client compatibility allows, to leverage the performance and security enhancements of TLS 1.3.
2. **Establish a Cipher Policy Lifecycle:** Institute an internal security policy that mandates the quarterly review and annual deprecation schedule for any cipher suite that falls below a specified industry standard strength (e.g., below 2048-bit for RSA or when a recognized breaking vulnerability exists).
3. **Adopt Hardened Server Defaults:** Move towards using established, vendor-recommended security configurations (e.g., Mozilla SSL Configuration Generator recommendations) rather than relying on default system settings.
## Implementation Guidance
### For Small Organizations
- **Use Platform Tools:** Leverage built-in configuration utilities provided by your hosting platform or load balancer (e.g., AWS ACM Certificate Manager policies, Apache/Nginx specific configuration modules) which often have pre-set "secure" templates.
- **Focus on Protocol Disablement:** Ensure the immediate and visible action is disabling SSLv2/v3, as this provides the fastest reduction in attack surface.
### For Medium Organizations
- **Automated Deployment:** Integrate cipher suite enforcement into configuration management tools (e.g., Ansible, Puppet) to ensure that security changes are consistently applied across all front-end servers during deployment or patching cycles.
- **A/B Testing:** Before fully deploying a new strict cipher policy, briefly deploy it to a subset of non-production or low-traffic environments to monitor for regressions or legitimate user connection failures.
### For Large Enterprises
- **Centralized Policy Management:** Mandate that TLS/SSL configuration standards are centrally managed and audited, ideally through a central WAF (Web Application Firewall) or hardware load balancer platform that governs all ingress traffic across diverse network segments.
- **Risk Acceptance Documentation:** For any necessary exceptions allowing older protocols or ciphers (e.g., for legacy internal systems), document the compensating controls and obtain formal risk acceptance from IT leadership.
## Configuration Examples
*(Since the specific configuration examples are not present in the provided text, this section refers to the necessary outcome of configuration.)*
**Desired Outcome for Cipher Configuration (Example using a modern preference):**
The configuration file must explicitly define the cipher string such that only modern, forward-secret suites are accepted and listed first:
`SSLCipherSuite ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256`
`SSLProtocol -all +TLSv1.2 +TLSv1.3` (Ensure SSLv2/v3/TLS 1.0/1.1 are explicitly disabled)
## Compliance Alignment
- **CIS Benchmarks:** Aligns directly with CIS Web Server Security Benchmarks, specifically regarding proper protocol and cipher suite negotiation.
- **PCI DSS Requirements (v4.0 Requirement 4.2):** Directly supports the requirement to use strong cryptography and securely configure all systems to protect cardholder data in transit.
- **NIST SP 800-52 Rev. 2:** Guidance on Secure Protocol and Cipher Suite Selection for Federal Information Systems.
## Common Pitfalls to Avoid
- **Relying on Defaults:** Do not assume that the default cipher and protocol settings provided by the operating system or web server software package are secure. Always override them.
- **Client Compatibility Over Security:** Avoid keeping weak ciphers active solely to support browsers that have not been updated in many years. Determine a reasonable cut-off for client support (e.g., TLS 1.2 minimum).
- **Inconsistent Implementation:** Applying strong cipher suites only on the primary public-facing load balancer, but failing to apply the same restrictions on backend application servers that might be directly exposed internally.
## Resources
- **Mozilla SSL Configuration Generator:** (Tool for generating secure Apache, Nginx, etc., configuration snippets.) [Defanged URL: `serverfault.com/ssl-configuration-generator`]
- **OpenSSL Documentation:** Guides on defining the `CipherString` list.
- **Qualys SSL Labs Server Test:** (Service for easily testing and measuring current configuration strength.) [Defanged URL: `ssllabs.com/ssltest/`]