Securing Remote Access With SSL VPNs: A Best Practice Primer

Securing Remote Access With SSL VPNs: A Best Practice Primer

Sikhi Gundu and Kartik Kumar, Juniper Networks India Pvt Ltd

Preliminaries

• Target audience: IT org managers, admins; not developers/implementers

• Introductory/high level overview• Essentially tutorial

Agenda

• Motivation• 30000ft view of SSLVPN Technology• Security with SSLVPN: Athentication• Security with SSLVPN: Endpoint Integrity

• Security with SSLVPN: Authorization• Security with SSLVPN: User Education

Agenda

• Motivation• 30000ft view of SSLVPN Technology• Security with SSLVPN: Authentication• Security with SSLVPN: Endpoint Integrity


Motivation

• Usecase• Remote access for Employees, Partners & Customers

• Why not IPSEC• Requires client software to be installed.• IPSEC VPNs are good for site-to-site, not so good for clients to server

• is layer 3; remote access users get layer 3 access!

• Why SSL VPN• Client less remote access (browser is the client)• Easy on the IT shop (roll-out, config)• Layer 4 access with notion of a " user "

Agenda



– SSLVPN device acts as a reverse proxy– SSL provides data confidentiality and integrity on the public network

Enterprise Network

SSLVPN basic workflow

Employees with Corporate/Home

Laptops

SSL VPN

App Server

Internet

https

https

http

http

SSL VPN typical deployment

EnterpriseNetwork

Internet

Firewall

Router

SSL VPN

Applications Server

Application Server

Employees with Corporate Laptops

Employeeswith Home PCs

Employees with Mobile Devices

SSLVPN – Typical End-user Flow• User connects to the gateway • User Authenticates

• SSLVPN presents portal frontending accessible resources

• User signs out.

Essential functionality: Rewriting

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•

• Layer 4

Essential Functionality: Rewriting Contd.• Layer 3

Src IP11.13.1.1

Dst IP12.2.2.3

Src IP11.13.1.1

Dst IP12.2.2.3

Src IP12.2.2.3

Dst IP10.2.2.4

Src IP12.2.2.3

Dst IP10.2.2.4

Applications Server

Src IP10.2.2.4

Dst IP12.2.2.3

Src IP10.2.2.4

Dst IP12.2.2.3

Src IP12.2.2.3

Dst IP11.13.1.1

Src IP12.2.2.3

Dst IP11.13.1.1

NAT Device

EnterpriseNetwork

Internet

Essential functionality: Granular Access Control

• Policy based access control (based on identity & other factors)

• For ex: assign role to user; assign resources to roles

• Example policies: • Web Access• UNIX file Access• Windows File Access• SSO• Terminal Services

Essential functionality: Granualar Access Control Contd…

• Example Role Assignments based on• Location• Username• Login time• Group• Etc etc.... Fine Grained Access control

• SSL VPN being a layer 4 device, has an end user notion and thus Fine Grained Access control Is possible

Agenda



Security with SSL VPN: Authentication

• Remember: Internet-facing device!• Ensure Strong Authentication

• Strength of Authentication• Strength of a password policy

– Password strength– Password expiry– Blacklisted pin dictionary

• Typically, device vendor would ensure protection against:

• Dictionary attacks• Brute force attacks• Denial of service attacks

• Single factor Authentication

• Two factor

Strong Authentication, Contd

Strength of Authentication Contd.

• Secondary Authentication

• Adaptive authentication

Strength of Authentication Contd.• Secondary Authentication

– Can be used where stronger auth mechanism is required.

– For example :• User does primary authentication to a Auth Server [could be certificate or Machine Auth]

• Once Primary auth succeeds, he has to authenticate again to a Secondary Auth Server [which could be AD or LDAP or radius auth]

• Secondary authentication combined with 2-factor, will be even more stronger, but an overkill.

Agenda



Assess Endpoint’s security posture• Enable this feature, most vendors provide it• Enforce policy not to allow login if client not clean• Makes sure that the client has

– Trusted anitivirus software (eg: Norton AV 2010)– Trusted Anti-MalWare– Updated database virus signatures for the antivirus.– Availabilty of OS Patches.

• Ensure file system has no suspicious content or processes.

• Ensure file system has the content it is supposed to have; ie, not tampered with

Clean session termination

• Data is left behind by the session!– Browser History– Browser Cache– Saved password and forms– Keystroke loggers– Cookies

• Use cache cleaning functionality– Cleans up all Browser data on logout

• Enable virtual keyboards during authentication

Clean session termination Contd.

• SVW [Secure virtual workspace]– Restricted, transient shell– Created when user login-in– Destroyed on logout– Ensures no upload of dangerous content or

download of critical data

Integrate with IDP

• Coordinated Threat control using IDP

IDP

SSL VPN

Detects intrusion

Quarantines user based on IDP instructions

Informs SSL VPN

Agenda



Security with SSLVPN: Authorization

• Can remote users have the same level of access privilege as local users? Maybe not!

• Exploit RBAC to the fullest• Role is a group of policies• Policies govern access to resources

– Web Recource Access– File Resource access [Both windows/UNIX]– Telnet/SSH Access– SSO – Terminal Services access

Role Based Access Control Contd.

• Vendors provide the ability to define roles as a function of several attributes

• For example:– Endpoint security posture– Login time– Login IP– Login Name– Directory attributes– Group– For ex: same user gets different privileges during

office hours as opposed to off-hours

Agenda



Bad people: evil outsiders and disgruntled insiders

• Remember: internet-facing web device• Vulnerable to the usual set of web attacks• Injection Attacks

– Most Common: Cross-site scripting• Parsing and detecting malicious script • Have multiple admins to verify config.

– New one XSRF• Cross site Request forgery

• Frame busting• Vendor provides some form of defence; but beware

your customization may open up holes!

Key is: Train your users

• Educate Users– Always ensure graceful exit– Don’t leave sessions unattended– Avoid logging in via Shared Computers– Don’t cache Password on browsers– Use Virtual keyboards for login

Thank you

Documents

Securing Remote Access With SSL VPNs: A Best Practice Primer