Bear with me readers, in this article I posit a controversial viewpoint. That viewpoint is that all existing technologies acting as proxies to transit security zones must be considered a security asset and that the security team needs to get more involved in load balancer design and operations.
What are we doing with proxies these days?
Working in information security and on the technical side of things you often get involved with the use of reverse and forward network proxies to transit security zones often defined by firewall appliances.
A reverse proxy terminates the flow of data from untrusted
networks in a semi-trusted network zone, your external De-Militarized Zone and
fetches data from a more trusted network zone. Your reverse proxy is meant to
have minimal functionality enabled and be security patched up to vendor
recommendations. The whole idea behind the reverse proxy is that even if a
vulnerability is exploited on it, at least it’s not in the core of your network
with access to everything.
A forward proxy fetches information from an untrusted network and returns it to a user or a system in a trusted network zone. Sometimes in large enterprises you will have user proxies and application proxies. The user proxies fetch content from the internet on behalf of the user and work on allowed categories that users are permitted to retrieve content from, whilst the application proxies allow internal systems to integrate only with whitelisted URLs they are allowed to post/get data to/from. The forward proxies simplify firewall rules and routing and help protect users and systems from retrieving malware or “phoning home” to malware command and control systems.
Proxies also should be used to terminate flows of encrypted data so that they can be inspected for malicious payload. With a DMZ located reverse proxy often an external CA issued digital certificate is installed, connecting to an internal CA issued digital certificate on the internal system. Private keys for these internal certificates can be loaded into intrusion detection and prevention systems etc. Sometimes these proxies are chained to Web Application Firewalls. With forward proxies, user computers are configured to trust internal CA issued certificates, which the forward proxy uses to perform TLS inspection.
Other “proxy technology” can include application specific forward DNS servers and NTP servers.
Why do we do this?
Historically we have only had north south network segregation. Hence web server vulnerabilities would result in access to underlying operating system and shared network segments. With a DMZ if a web server is compromised, maybe all web servers end up being owned through lateral “pivoting”, but at least not the database servers.
Often the only reason we are running apache in a DMZ as a reverse proxy is “because security told us” or “that’s how we’ve always done it” or because that is usually how the vendor of the application commonly deploys it.
Developers would love to just run apache and tomcat on the same host, or heck just tomcat. Often Apache acting as a reverse proxy adds no application functionality, except for hosting a “sorry we’re down” static web page during maintenance outages. In many cases the web server in the DMZ is just hosting a “plugin” that fetches content from another web server on the application server.
How are things changing?
Load balancers also known as Application Delivery Controllers are able to perform TLS re-termination and act as reverse proxies. The main point of ingress into network zones is now the load balancer.
Cloud based user forward proxies are becoming more popular as they provide the ability to protect mobile workers with the same surveillance and security policy as on premise users.
Newer versions of TLS are likely to implement Perfect Forward Security (PFS) and the use of static encryption keys will be deprecated.
Slowly but surely East West Network segregation is coming in via the new buzzword in town Software Defined Networking (SDN). With SDN you can have virtual network setups for each key application and allow interactions with other key applications on principle of least privilege. East West segregation essentially turns every application into a “silo” and allows communications between them on principle of least privilege, restricting lateral movement by an attacker in datacentre networks. The days of physical network appliances physically wired to switches, routers and servers are numbered. The security market is moving more and more towards the build of reference models and QA review of deployment scripts which drive the build/secure configuration of application, server and network infrastructure.
Often proxy logs are being mined to identify malware command and control communications, as once the proxy is the sole method of communication with the internet for most users and systems, all malware communications go through it.
So what as a security team should we be doing?
The enterprise security function must take on responsibility for security policy on web servers that perform reverse proxy capabilities.
Enterprise security must take on responsibility for governing security policy implementation on application delivery controllers leveraging all native capabilities available such as TLS configuration, Layer 3 filtering, Layer 7 filtering, content inspection and identity and access management integration.
The security function must retain the responsibility for governance of security policy on forward proxies and tweak the policy to restrict the download of “dangerous file types” only from trusted web sites (e.g. only allow .exe downloads from trusted vendor websites) and look seriously at implementing user behaviour driven anomaly detection as well as sandboxing to detect malicious PDFs etc.
The security function must work with network architecture to see if the functions of tier 1 firewall, forward proxy and web server can be collapsed. Perhaps this can be accomplished with load balancers to simplify the network topology and allow us to deploy security policy in a single place? If a virtual load balancer can deliver secure layer 3 stateful firewalling capability, do we even need tier 1 firewalls in front of them?
The security function must plan to support newer versions of TLS which may implement perfect forward security whilst maintaining the ability to inspect web content coming into our DMZ.
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