SSL/TLS

Modern Testing Tools

# Comprehensive TLS testing (recommended)
# testssl.sh - https://github.com/drwetter/testssl.sh
testssl.sh https://example.com

# With specific checks
testssl.sh --vulnerable https://example.com
testssl.sh --cipher-per-proto https://example.com

# SSLyze - Python-based
# https://github.com/nabla-c0d3/sslyze
sslyze --regular example.com:443

# tlsx - Fast TLS prober
# https://github.com/projectdiscovery/tlsx
tlsx -u example.com -port 443

# Nmap SSL scripts
nmap --script ssl-* -p 443 example.com

2025 Best Practices

Recommended Configuration

# Protocols
✅ TLS 1.3 (preferred)
✅ TLS 1.2 (acceptable)
❌ TLS 1.1 (deprecated)
❌ TLS 1.0 (deprecated)
❌ SSLv3 (insecure)
❌ SSLv2 (insecure)

# Cipher Suites (TLS 1.3)
TLS_AES_256_GCM_SHA384
TLS_CHACHA20_POLY1305_SHA256
TLS_AES_128_GCM_SHA256

# Cipher Suites (TLS 1.2)
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

# Key Exchange
✅ ECDHE (Elliptic Curve Diffie-Hellman Ephemeral)
⚠️ DHE (only with 2048+ bit parameters)
❌ RSA key exchange (no forward secrecy)
❌ DH < 2048 bits

# Certificates
✅ RSA 2048+ bits or ECDSA 256+ bits
✅ SHA-256 or better signature
❌ SHA-1 signatures
❌ MD5 signatures

Quick Vulnerability Checks

# Check supported protocols
openssl s_client -connect example.com:443 -tls1_3
openssl s_client -connect example.com:443 -tls1_2
openssl s_client -connect example.com:443 -tls1_1
openssl s_client -connect example.com:443 -tls1

# Check certificate details
openssl s_client -connect example.com:443 </dev/null 2>/dev/null | openssl x509 -noout -text

# Check certificate expiry
echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

# Check certificate chain
openssl s_client -connect example.com:443 -showcerts

DROWN

# Check for "SSLv2 supported"
nmap -p- -sV -sC example.com
testssl.sh --drown example.com

TLS_FALLBACK_SCSV

# Check in the lower port
openssl s_client –tls1 -fallback_scsv -connect example.com:443
# - Response:
# tlsv1 alert inappropriate fallback:s3_pkt.c:1262:SSL alert number 86

BEAST

# TLSv1.0 and CBC ciphers
openssl s_client -[sslv3/tls1] -cipher CBC_CIPHER -connect example.com:443

LUCKY13

openssl s_client -cipher CBC_CIPHER -connect example.com:443

Sweet32

openssl s_client -cipher 3DES -connect example.com:443

Logjam

# Check the "Server Temp Key" response is bigger than 1024 (only in OpenSSL 1.0.2 or better)
openssl s_client -connect www.example.com:443 -cipher "EDH"

SSLv2 Support

# If is supported this will return the server certificate information if not, error
openssl s_client –ssl2 -connect example.com:443

SSLv3 Support

# If is supported this will return the server certificate information if not, error
openssl s_client -ssl3 -connect google.com:443

Cipher suites

# Cipher Suites
nmap --script ssl-enum-ciphers -p 443 example.com

# - Anon cypher (fail)
openssl s_client -cipher aNULL -connect example.com:443

# - DES Cipher (fail)
openssl s_client -cipher DES -connect example.com:443

# - 3DES Cipher (fail)
openssl s_client -cipher 3DES -connect example.com:443

# - Export Cipher (fail)
openssl s_client -cipher EXPORT -connect example.com:443

# - Low Cipher (fail)
openssl s_client -cipher LOW -connect example.com:443

# - RC4 Cipher (fail)
openssl s_client -cipher RC4 -connect example.com:443

# - NULL Cipher (fail)
openssl s_client -cipher NULL -connect example.com:443

# - Perfect Forward Secrecy Cipher (This should NOT fail):
openssl s_client -cipher EECDH, EDH NULL -connect example.com:443

Secure renegotiation

# Check secure renegotiation is not supported
# If not, send request in the renegotiation
# Once sent, if it's vulnerable it shouldn't return error
openssl s_client -connect example.com:443
HEAD / HTTP/1.0
R
# <Enter or Return key>

CRIME

# Check for "Compression: NONE"
openssl s_client -connect example.com:443

BREACH

# If the response contains encoded data, host is vulnerable
openssl s_client -connect example.com:443
GET / HTTP/1.1
Host: example.com
Accept-Encoding: compress, gzip

Heartbleed

# Heartbleed
nmap -p 443 --script ssl-heartbleed --script-args vulns.showall example.com

# Heartbleed checker oneliner from sites list
cat list.txt | while read line ; do echo "QUIT" | openssl s_client -connect $line:443 2>&1 | grep 'server extension "heartbeat" (id=15)' || echo $line: safe; done

Change cipher spec injection

nmap -p 443 --script ssl-ccs-injection example.com

Cipher order enforcement

# Choose a protocol and 2 different ciphers, one stronger than other
# Make 2 request with different cipher order anc check in the response if the cipher is the first of the request in both cases
nmap -p 443 --script ssl-enum-ciphers example.com
openssl s_client –tls1_2 –cipher ‘AES128-GCM-SHA256:AES128-SHA’ –connect contextis.co.uk:443
openssl s_client –tls1_2 –cipher ‘AES128-SHA:AES128-GCM-SHA256’ –connect contextis.co.uk:443

Additional Vulnerabilities

POODLE

# SSLv3 + CBC = vulnerable
openssl s_client -ssl3 -connect example.com:443
testssl.sh --poodle example.com

ROBOT

# Return Of Bleichenbacher's Oracle Threat
# RSA key exchange vulnerability
testssl.sh --robot example.com

Certificate Issues

# Check for certificate issues
testssl.sh --cert example.com

# Common issues:
# - Expired certificate
# - Self-signed certificate
# - Wrong hostname (CN/SAN mismatch)
# - Weak signature algorithm (SHA-1, MD5)
# - Short key length (< 2048 bits RSA)
# - Missing intermediate certificates

Resources

• SSL Labs Server Test

• testssl.sh

• Mozilla SSL Configuration Generator

• OWASP TLS Cheat Sheet