1# TLS 1.3 only allows these 5 cipher suites — all AEAD:
2TLS_AES_256_GCM_SHA384       # AES-256 in GCM mode
3TLS_AES_128_GCM_SHA256       # AES-128 in GCM mode
4TLS_CHACHA20_POLY1305_SHA256 # ChaCha20 stream cipher (great on mobile)
5TLS_AES_128_CCM_SHA256       # AES-128 in CCM mode
6TLS_AES_128_CCM_8_SHA256     # AES-128 in CCM mode (8-byte tag)
7
8# Compare with TLS 1.2 which supports 300+ cipher suites,
9# many of which are weak or broken.

1# Normal connection (TLS 1.3):
2Client → Server: ClientHello (TLS 1.3, strong ciphers)
3Server → Client: ServerHello (TLS 1.3, AES-256-GCM)
4# ✅ Secure connection established
5
6# MITM downgrade attack (if server supports TLS 1.0):
7Client → MITM → Server: ClientHello (TLS 1.3, strong ciphers)
8MITM modifies: ClientHello (TLS 1.0, weak ciphers)
9Server → MITM → Client: ServerHello (TLS 1.0, RC4-SHA)
10# ❌ Weak connection — MITM can decrypt traffic!
11
12# Prevention: TLS_FALLBACK_SCSV (RFC 7507) detects downgrades
13# But the real fix: disable TLS 1.0 and 1.1 entirely

1# ✅ Strong cipher suite list for TLS 1.2 (Mozilla "Modern" profile):
2TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
3TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
4TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
5TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
6TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
7TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
8
9# Key properties of ALL recommended suites:
10# - ECDHE: Ephemeral key exchange → forward secrecy ✓
11# - GCM or POLY1305: AEAD encryption → no padding oracle ✓
12# - AES-128/256 or ChaCha20: Strong symmetric encryption ✓
13
14# ❌ Cipher suites to NEVER enable:
15# - Anything with NULL, EXPORT, DES, 3DES, RC4
16# - Anything with RSA key exchange (not ECDHE_RSA — static RSA)
17# - Anything with MD5 MAC

1// ❌ CRITICAL: Disabling TLS certificate verification
2// This is the most dangerous TLS mistake in application code
3
4// Node.js — disabling verification globally
5process.env.NODE_TLS_REJECT_UNAUTHORIZED = '0';
6
7// Node.js — per-request
8const https = require('https');
9const agent = new https.Agent({ rejectUnauthorized: false });
10fetch('https://api.example.com', { agent });
11
12// Python requests
13import requests
14requests.get('https://api.example.com', verify=False)
15
16// Java
17TrustManager[] trustAll = new TrustManager[] {
18  new X509TrustManager() {
19    public X509Certificate[] getAcceptedIssuers() { return null; }
20    public void checkClientTrusted(X509Certificate[] c, String t) {}
21    public void checkServerTrusted(X509Certificate[] c, String t) {}
22  }
23};
24
25// Go
26http.Client{
27  Transport: &http.Transport{
28    TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
29  },
30}
31
32// All of the above: COMPLETELY DISABLES CERTIFICATE VERIFICATION
33// A MITM attacker can present ANY certificate and it will be accepted!

1# User types "example.com" in browser (no https:// prefix):
2# 1. Browser sends HTTP request to http://example.com
3# 2. Server redirects: HTTP 301 → https://example.com
4# 3. Browser follows redirect to HTTPS
5
6# SSL Stripping MITM attack (Moxie Marlinspike, 2009):
7# 1. User sends HTTP request to http://example.com
8# 2. MITM intercepts and connects to https://example.com on user's behalf
9# 3. MITM returns HTTP response to user (not HTTPS!)
10# 4. User sees http://example.com — no padlock, but many users don't notice
11# 5. ALL traffic flows through MITM in plaintext — credentials stolen!
12
13# The user thinks they're on the real site.
14# The server thinks it's talking to the user over HTTPS.
15# The MITM reads everything.

1# ✅ HSTS tells the browser: "NEVER connect over HTTP"
2Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
3
4# max-age=31536000     → Remember for 1 year (in seconds)
5# includeSubDomains    → Apply to all subdomains too
6# preload              → Eligible for browser's built-in HSTS preload list
7
8# After receiving this header over HTTPS, the browser will:
9# - Automatically convert ALL http:// requests to https://
10# - Refuse to connect if the certificate is invalid (no "click through")
11# - Remember this policy for max-age seconds
12
13# ❌ INSECURE: Common mistakes
14Strict-Transport-Security: max-age=0           # Disables HSTS!
15Strict-Transport-Security: max-age=3600        # Only 1 hour — too short
16# Missing entirely                              # No HSTS protection at all

1# Disabled certificate verification
2grep -rn "rejectUnauthorized.*false|REJECT_UNAUTHORIZED.*0"   --include="*.js" --include="*.ts" --include="*.env"
3
4grep -rn "verify.*=.*False|verify.*False"   --include="*.py"
5
6grep -rn "InsecureSkipVerify.*true"   --include="*.go"
7
8# Weak protocols in config
9grep -rn "SSLv2|SSLv3|TLSv1.0|TLSv1.1|ssl_protocols.*TLSv1[^.]"   --include="*.conf" --include="*.yaml" --include="*.yml"
10
11# Weak ciphers
12grep -rn "RC4|DES|NULL|EXPORT|3DES|aNULL|eNULL"   --include="*.conf" --include="*.yaml" --include="*.yml"
13
14# Missing HSTS (check server framework middleware)
15grep -rn "strict-transport|hsts|Strict-Transport"   --include="*.js" --include="*.ts" --include="*.conf"
16
17# Mixed content
18grep -rn "http://" --include="*.html" --include="*.tsx" --include="*.jsx"   | grep -v "localhost|127.0.0.1|http://schemas"
19
20# External scan: SSL Labs server test
21# https://www.ssllabs.com/ssltest/