Kryptografie/Proxy

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Proxy Solutions

Within enterprise networks and corporations with increased levels of paranoia or at least some defined security requirements it is common not to allow direct connections to the public internet. For this reason proxy solutions are deployed on corporate networks to intercept and scan the traffic for potential threats within sessions. For encrypted traffic there are four options:* Block the connection because it cannot be scanned for threats.

  • Bypass the threat-mitigation and pass the encrypted session to the client, which results in a situation where malicious content is transferred directly to the client without visibility to the security system.
  • Intercept (i.e. terminate) the session at the proxy, scan there and re-encrypt the session towards the client (effectively MITM).
  • Deploy special Certificate Authorities to enable Deep Packet Inspection on the wire.

While the latest solution might be the most "up to date", it arises a new front in the context of this paper, because the most secure part of a client’s connection could only be within the corporate network, if the proxy-server handles the connection to the destination server in an insecure manner. Conclusion: Don’t forget to check your proxy solutions SSL-capabilities. Also do so for your reverse proxies!

Bluecoat / Symantec

Blue Coat Systems was a well-known manufacturer of enterprise proxy appliances. In 2016 it was acquired by Symantec. The products are now known as Symantec ProxySG and Advanced Secure Gateway (ASG). The description below is for the original Blue Coat SG Operating System (SGOS). BlueCoat Proxy SG Appliances can be used as forward and reverse proxies. The reverse proxy feature is rather under-developed, and while it is possible and supported, there only seems to be limited use of this feature "in the wild" - nonetheless there are a few cipher suites to choose from, when enabling SSL features.

Tested with Versions

Proxy Appliance SGOS 6.5.x Blue Coat, now Symantec

Only allow TLS 1.0,1.1 and 1.2 protocols

$conf t
$(config)ssl
$(config ssl)edit ssl-device-profile default
$(config device-profile default)protocol tlsv1 tlsv1.1 tlsv1.2
 ok

Select your accepted cipher-suites

$conf t
Enter configuration commands, one per line.  End with CTRL-Z.
$(config)proxy-services
$(config proxy-services)edit ReverseProxyHighCipher
$(config ReverseProxyHighCipher)attribute cipher-suite
Cipher#  Use        Description        Strength
-------  ---   -----------------------   --------
     1  yes            AES128-SHA256      High
     2  yes            AES256-SHA256      High
     3  yes               AES128-SHA    Medium
     4  yes               AES256-SHA      High
     5  yes       DHE-RSA-AES128-SHA      High
     6  yes       DHE-RSA-AES256-SHA      High
              [...]
    13  yes          EXP-RC2-CBC-MD5    Export
Select cipher numbers to use, separated by commas: 2,5,6
 ok


The same protocols are available for forward proxy settings and should be adjusted accordingly: In your local policy file add the following section: <ssl> 

   DENY server.connection.negotiated_ssl_version=(SSLV2, SSLV3)

Disabling protocols and ciphers in a forward proxy environment could lead to unexpected results on certain (misconfigured?) webservers (i.e. ones accepting only SSLv2/3 protocol connections)

HAProxy

See https://www.haproxy.org/ See https://timtaubert.de/blog/2014/11/the-sad-state-of-server-side-tls-session-resumption-implementations/ See https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#5.1-npn See https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#3.2-tune.ssl.cachesize See https://kura.io/2014/07/02/haproxy-ocsp-stapling/ See https://kura.io/2015/01/27/hpkp-http-public-key-pinning-with-haproxy/ HAProxy can be used as loadbalancer and proxy for TCP and HTTP-based applications. Since version 1.5 it supports SSL and IPv6.

Tested with Versions

HAProxy 1.5.11 with OpenSSL 1.0.1e on Debian Wheezy

Settings

global configuration

global 

   ssl-default-bind-ciphers 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
   ssl-default-bind-options no-sslv3 no-tls-tickets #disable SSLv3
   tune.ssl.default-dh-param 2048 #tune DH to 2048
frontend configuration

frontend public 

   bind *:80
   bind *:443 ssl crt server.pem
   mode http
   redirect scheme https code 301 if !{ ssl_fc } # redirect HTTP to HTTPS
backend configuration

backend backend 

   mode http
   server server 192.168.1.1:80 check
   http-request set-header X-Forwarded-Port %[dst_port]
   http-request add-header X-Forwarded-Proto https if { ssl_fc }
   rspadd Strict-Transport-Security:\ max-age=15768000;\ includeSubDomains #enable HSTS header for this backend

Additional Settings

Enable NPN Support:

   bind *:443 ssl crt server.pem npn "http/1.1,http/1.0"

Append the npn command in the frontend configuration of HAProxy.

Enable OCSP stapling:

HAProxy supports since version 1.5.0 OCSP stapling. To enable it you have to generate the OCSP singing file in the same folder, with the same name as your certificate file plus the extension .ocsp. (e.g. your certificate file is named server.crt then the OCSP file have to be named server.crt.oscp)To generate the OCSP file use these commands: $ openssl x509 -in your.certificate.crt -noout -ocsp_uri # <- get your ocsp uri $ openssl ocsp -noverify -issuer ca.root.cert.crt -cert your.certificate.crt -url "YOUR OCSP URI" -respout your.certificate.crt.ocsp Reload HAProxy and now OCSP stapling should be enabled.Note: This OCSP signature file is only valid for a limited time. The simplest way of updating this file is by using cron.daily or something similar.

Enable HPKP:

Get certificate informations: $ openssl x509 -in server.crt -pubkey -noout | openssl rsa -pubin -outform der | openssl dgst -sha256 -binary | base64 Then you append the returned string in the HAProxy configuration. Add the following line to the backend configuration: rspadd Public-Key-Pins:\ pin-sha256="YOUR_KEY";\ max-age=15768000;\ includeSubDomains Reload HAProxy and HPKP should now be enabled.Note: Keep in mind to generate a backup key in case of problems with your primary key file.

How to test

See appendix Tools

Pound

Tested with Versions

Pound 2.6 See http://www.apsis.ch/pound See https://help.ubuntu.com/community/Pound

Settings

HTTPS Listener in Pound
# HTTP Listener, redirects to HTTPS
ListenHTTP
   Address 10.10.0.10
   Port    80
   Service
       Redirect "https://some.site.tld"
   End
End
## HTTPS Listener
ListenHTTPS
   Address      10.10.0.10
   Port         443
   AddHeader    "Front-End-Https: on"
   Cert         "/path/to/your/cert.pem"
    ## See 'man ciphers'.
   Ciphers "TLSv1.2:TLSv1.1:!SSLv3:!SSLv2: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"
   Service
       BackEnd
           Address 10.20.0.10
           Port 80
       End
   End
End

stunnel

Tested with Versions

  • stunnel 4.53-1.1ubuntu1 on Ubuntu 14.04 Trusty with OpenSSL 1.0.1f, without disabling Secure Client-Initiated Renegotiation
  • stunnel 5.02-1 on Ubuntu 14.04 Trusty with OpenSSL 1.0.1f
  • stunnel 4.53-1.1 on Debian Wheezy with OpenSSL 1.0.1e, without disabling Secure Client-Initiated Renegotiation

Settings

HTTPS Listener in stunnel
ciphers = 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
curve = secp384r1
options = NO_SSLv2
options = NO_SSLv3
options = cipher_server_preference
; Secure Client-Initiated Renegotiation can only be disabled wit stunnel >= 4.54
;renegotiation = no

Additional information

Secure Client-Initiated Renegotiation can only be disabled for stunnel versions >= 4.54, when the renegotiation parameter has been added (See changelog).

References

stunnel documentation: https://www.stunnel.org/static/stunnel.html stunnel changelog: https://www.stunnel.org/sdf_ChangeLog.html

How to test

See appendix Tools


Anhang

Siehe auch

Sicherheit

Dokumentation

Links

Projekt
Weblinks
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