Cheat Sheets

Security - nginx SSL Certs


An nginx production webserver should not use weak certificates. Checks for weak signatures (better than SHA-256) and RSA public key size (>=4096)


  • NIST-800-57

Check Script:


# solution: You need to create a new certificate with stronger signing signature and/or RSA public key size

for dir in /etc/nginx /usr/local/nginx/conf; do if [ -d $dir ]; then while read -r c; do c=${c//[\'\"]} x=$(openssl x509 -in "$c" -text)

# Check for weak signature algorithm if echo "$x" | grep -q "Signature Algorithm: sha1WithRSAEncryption"; then result_failed "$c is SHA-1 signed which is insecure!" elif echo "$x" | grep -q "Signature Algorithm: sha256WithRSAEncryption"; then result_warning "$c is SHA-256 signed and might be insecure." fi

# Check for insufficient RSA key sizes key_size=$( echo "$x" | grep "RSA Public Key: ([0-9][0-9]* bit)" |\ sed 's/.*(\([0-9][0-9]*\) bit).*/\1/' ) if [ "$key_size" != "" ]; then if [ "$key_size" -lt 1024 ]; then result_failed "$c has public key size '$key_size' which is insecure!" elif [ "$key_size" -lt 4096 ]; then result_warning "$c has public key size '$key_size' which is insufficient (should be >=4096)" fi fi

# Check for expired/expiring certs (1 week) if ! openssl x509 -checkend 604800 -noout -in "$c"; then result_failed "$c expired/expire soon ($(openssl x509 -enddate -noout -in "$c"))." fi done < <( grep -h "^[^#]*ssl_certificate[^_]" "$dir/"*-enabled/* 2>/dev/null |\ sed 's/^.*ssl_certificate *//;s/;//' ) fi done