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Weak SSL/TLS Configuration

Gixy Check ID: weak_ssl_tls

Overview

The weak_ssl_tls plugin detects insecure SSL/TLS configurations that may compromise the security of encrypted connections. This includes outdated protocols, weak cipher suites, and client-driven cipher selection.

What it detects

1. Insecure TLS Protocols

Detects use of deprecated protocols that are vulnerable to attacks:

Protocol Status Vulnerabilities
SSLv2 ❌ Insecure Multiple critical flaws
SSLv3 ❌ Insecure POODLE attack
TLSv1.0 ❌ Insecure BEAST, POODLE, CRIME
TLSv1.1 ❌ Insecure Weak ciphers, no AEAD
TLSv1.2 ✅ Secure Use with strong ciphers
TLSv1.3 ✅ Secure Modern, recommended

2. Weak Cipher Suites

Detects cipher suites that should be avoided:

  • NULL ciphers - No encryption at all
  • EXPORT ciphers - Intentionally weakened (40-56 bit)
  • DES/3DES - Vulnerable to Sweet32 attack
  • RC4 - Broken stream cipher
  • Anonymous ciphers (ADH/AECDH) - No authentication
  • MD5-based ciphers - Weak hash function

3. Server Cipher Preference

Detects when ssl_prefer_server_ciphers is disabled, allowing clients to choose potentially weaker ciphers.

Examples

❌ Bad: Insecure protocols enabled

server {
    listen 443 ssl;
    ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;  # SSLv3, TLSv1, TLSv1.1 are insecure
}
Issue: Insecure protocols enabled: SSLv3, TLSv1, TLSv1.1

❌ Bad: Weak ciphers

server {
    listen 443 ssl;
    ssl_ciphers ALL:RC4:DES:3DES;  # Includes weak ciphers
}
Issue: Weak ciphers found: RC4, DES, 3DES

✅ Good: Secure configuration

server {
    listen 443 ssl;

    # Modern protocols only
    ssl_protocols TLSv1.2 TLSv1.3;

    # Mozilla Intermediate cipher suite
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;

    # Server chooses cipher
    ssl_prefer_server_ciphers on;

    # HSTS is checked by the dedicated `hsts_header` plugin.
}

Based on Mozilla's SSL Configuration Generator:

ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;
ssl_prefer_server_ciphers off;

Modern Configuration (TLSv1.3 only)

ssl_protocols TLSv1.3;
ssl_prefer_server_ciphers off;

Why This Matters

Weak SSL/TLS configurations expose your server to:

  1. POODLE Attack (SSLv3) - Allows decryption of secure connections
  2. BEAST Attack (TLSv1.0) - Allows decryption of HTTPS cookies
  3. Sweet32 Attack (3DES) - Allows recovery of plaintext from long connections
  4. RC4 Bias - Allows plaintext recovery from encrypted streams
  5. Downgrade Attacks - Force use of weaker protocols

Testing Your Configuration

Use these tools to verify your SSL/TLS configuration:

References

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