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Weak SSH/SSL protocols and ciphers & hardening

July 31, 2017, 1:37 pm
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Sammlung aller SSH/SSL relevanten und meist genutzten Dienste und deren optimale SSH/SSL Konfiguration.

Apache / Nginx

apache 2.4.18 | modern profile | OpenSSL 1.0.1e

Oldest compatible clients: Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, and Java 8

<VirtualHost *:443>
    ...
    SSLEngine on
    SSLCertificateFile      /path/to/signed_certificate_followed_by_intermediate_certs
    SSLCertificateKeyFile   /path/to/private/key

    # Uncomment the following directive when using client certificate authentication
    #SSLCACertificateFile    /path/to/ca_certs_for_client_authentication


    # HSTS (mod_headers is required) (15768000 seconds = 6 months)
    Header always set Strict-Transport-Security "max-age=15768000"
    ...
</VirtualHost>

# modern configuration, tweak to your needs
SSLProtocol             all -SSLv3 -TLSv1 -TLSv1.1
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:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256
SSLHonorCipherOrder     on
SSLCompression          off
SSLSessionTickets       off

# OCSP Stapling, only in httpd 2.3.3 and later
SSLUseStapling          on
SSLStaplingResponderTimeout 5
SSLStaplingReturnResponderErrors off
SSLStaplingCache        shmcb:/var/run/ocsp(128000)

nginx 1.10.1 | modern profile | OpenSSL 1.0.1e

Oldest compatible clients: Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, and Java 8

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # Redirect all HTTP requests to HTTPS with a 301 Moved Permanently response.
    return 301 https://$host$request_uri;
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    # certs sent to the client in SERVER HELLO are concatenated in ssl_certificate
    ssl_certificate /path/to/signed_cert_plus_intermediates;
    ssl_certificate_key /path/to/private_key;
    ssl_session_timeout 1d;
    ssl_session_cache shared:SSL:50m;
    ssl_session_tickets off;


    # modern configuration. tweak to your needs.
    ssl_protocols TLSv1.2;
    ssl_ciphers '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:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256';
    ssl_prefer_server_ciphers on;

    # HSTS (ngx_http_headers_module is required) (15768000 seconds = 6 months)
    add_header Strict-Transport-Security max-age=15768000;

    # OCSP Stapling ---
    # fetch OCSP records from URL in ssl_certificate and cache them
    ssl_stapling on;
    ssl_stapling_verify on;

    ## verify chain of trust of OCSP response using Root CA and Intermediate certs
    ssl_trusted_certificate /path/to/root_CA_cert_plus_intermediates;

    resolver <IP DNS resolver>;

    ....
}

Quelle: https://mozilla.github.io/server-side-tls/ssl-config-generator/

SSL Webserver Test

Qualys hat eine tolle SSL Analyse Webseite, Link: https://www.ssllabs.com/ssltest/

Beispiel google.de:

Es zeigt einen schnellen Überblick plus sehr detailierte Informationen was nicht passt oder was man verbessern kann.

Alternative check with nmap

max@cmkdevel:~$ nmap --script ssl-cert,ssl-enum-ciphers -p 443 www.google.de            

Starting Nmap 7.01 ( https://nmap.org ) at 2017-08-01 09:08 CEST
Nmap scan report for www.google.de (172.217.17.35)
Host is up (0.031s latency).
Other addresses for www.google.de (not scanned): 2a00:1450:400e:804::2003
rDNS record for 172.217.17.35: ams16s29-in-f3.1e100.net
PORT    STATE SERVICE
443/tcp open  https
| ssl-cert: Subject: commonName=www.google.de/organizationName=Google Inc/stateOrProvinceName=California/countryName=US
| Issuer: commonName=Google Internet Authority G2/organizationName=Google Inc/countryName=US
| Public Key type: rsa
| Public Key bits: 2048
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2017-07-19T11:48:30
| Not valid after:  2017-10-11T11:31:00
| MD5:   f21e dd1d 579f 5ea3 1b3d 2e79 873d 616c
|_SHA-1: f2af ac3f fb43 20be 9f6a b0fc 9356 808a f677 86fc
| ssl-enum-ciphers: 
|   TLSv1.0: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (secp256r1) - A
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (secp256r1) - A
|       TLS_RSA_WITH_AES_128_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA (rsa 2048) - C
|     compressors: 
|       NULL
|     cipher preference: server
|   TLSv1.1: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (secp256r1) - A
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (secp256r1) - A
|       TLS_RSA_WITH_AES_128_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA (rsa 2048) - C
|     compressors: 
|       NULL
|     cipher preference: server
|   TLSv1.2: 
|     ciphers: 
|       TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (secp256r1) - A
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (secp256r1) - A
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (secp256r1) - A
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (secp256r1) - A
|       TLS_RSA_WITH_AES_128_GCM_SHA256 (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_GCM_SHA384 (rsa 2048) - A
|       TLS_RSA_WITH_AES_128_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA (rsa 2048) - C
|     compressors: 
|       NULL
|     cipher preference: server
|_  least strength: C

Nmap done: 1 IP address (1 host up) scanned in 3.31 seconds

Postfix

/etc/postfix/main.cf

smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_mandatory_ciphers=high

tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA

smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA, KRB5-DES, CBC3-SHA

smtpd_tls_dh1024_param_file=/etc/ssl/dh2048.pem

smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtp_tls_protocols = !SSLv2, !SSLv3

lmtp_tls_mandatory_protocols = !SSLv2, !SSLv3
lmtp_tls_protocols = !SSLv2, !SSLv3

smtp_tls_security_level = may
smtp_tls_loglevel = 1

smtpd_tls_auth_only = yes

Generate new Diffie Hellman Keys

openssl dhparam -out /etc/ssl/dh2048.pem 2048

Restart Postfix

service postfix restart

Mehr: http://www.postfix.org/TLS_README.html

Check Postfix SSL Configuration

Test mit openssl s_client

openssl s_client -starttls smtp -connect mailserver.example.org:25

Alternative mit nmap

nmap --script ssl-cert,ssl-enum-ciphers -p 993,995,25,587 -Pn mailserver.example.org

Dovecot

/etc/dovecot/conf.d/10-ssl.conf

ssl_cipher_list = EECDH+ECDSA+AESGCM:EECDH+aRSA+AESGCM:EECDH+ECDSA+SHA384:EECDH+ECDSA+SHA256:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH+aRSA+RC4:EECDH:EDH+aRSA:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4
#only for dovecot >=2.2.6, enforce the server cipher preference
ssl_prefer_server_ciphers = yes
#disable SSLv2 and SSLv3
ssl_protocols = !SSLv2 !SSLv3

Restart dovecot

service dovecot restart

Überprüfen mit openssl s_connect

openssl s_client -connect mailserver.example.org:993
openssl s_client -connect mailserver.example.org:995

Alternative mit nmap

nmap --script ssl-cert,ssl-enum-ciphers -p 993,995 -Pn mailserver.example.org

SSH

/etc/ssh/sshd_config

# Remove dsa hostkeys
HostKey /etc/ssh/ssh_host_ed25519_key
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key

KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes256-ctr
Macs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-256

AuthenticationMethods publickey
LogLevel VERBOSE
Subsystem sftp  /usr/lib/ssh/sftp-server -f AUTHPRIV -l INFO
PermitRootLogin No
UsePrivilegeSeparation sandbox

Achtung ! DSA SSH Keys werden danach nicht mehr funktionieren.

Quelle: https://github.com/mozilla/wikimo_content/blob/master/Security/Guidelines/OpenSSH.mediawiki#Modern_OpenSSH_67

Restart SSH

service ssh restart

OpenVPN

/etc/openvpn/openvpn.conf

tls-version-min 1.2
tls-cipher TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384
cipher AES-256-CBC
auth SHA512
reneg-sec 60

Quelle: https://community.openvpn.net/openvpn/wiki/Hardening / https://gist.github.com/pwnsdx/8fc14ee1e9f561a0a5b8

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