What is a proxy server?

How proxy servers work

When a proxy server receives a request for an internet resource such as a webpage, it looks in its local cache of previously accessed pages. If it finds the page, it returns it to the user without needing to forward the request to the internet. If the page isn't in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own Internet Protocol (IP) addresses to request the page from the server out on the internet. When the page is returned, the proxy server relates it to the original request and forwards it to the user.

Proxy servers are used for both legal and illegal purposes. In the enterprise, a proxy server is used to facilitate security, administrative control or caching services, among other purposes. In a personal computing context, proxy servers are used to enable user privacy and anonymous surfing. Proxy servers can also be used for the opposite purpose: to monitor traffic and undermine user privacy.

To the user, the proxy server is invisible, and all internet requests and returned responses appear to be directly interacting with the addressed internet server. However, the proxy isn't actually invisible, as its IP address must be specified as a proxy configuration option to the browser or other protocol program.

How users can configure a proxy server

Users can access web proxies online or configure web browsers to constantly use a proxy server. Browser proxy settings include automatically detected and manual options for HTTP, Secure Sockets Layer (SSL), File Transfer Protocol, and Socket Secure or Socks proxies.

Proxy servers can serve many users or just one per server. These options are called shared and dedicated proxies, respectively. There are several reasons for proxies and thus many types of proxy servers, often in overlapping categories.

When configuring proxy servers, variations in steps across operating systems (OSes) and devices, such as Microsoft Windows or macOS, can occur due to updates or specific software versions. Users should review the documentation supplied by their proxy service provider or the official documentation of their OS for precise instructions.

Benefits of a proxy server

Using a proxy server can provide various advantages to organizations and individuals, including the following:

• Improved security. Proxy servers bolster security by providing content filtering and serving as a firewall and a web filter, safeguarding users against malware and other cyberattacks. They can also encrypt web requests, which adds an extra layer of protection for sensitive data.
• Efficient monitoring of internet usage. Businesses and individuals can use proxy servers to regulate and monitor internet usage by restricting access to specific websites during work or study hours. Proxy servers also enable tracking and logging of online requests, providing insight into user behavior, even in situations where website restrictions aren't entirely enforced. This enables more effective enforcement of laws against cyberloafing, which involves employees using work time for nonwork-related activities.
• Privacy and anonymity. By changing the user's IP address, proxy servers enable anonymous browsing, masking the user's location and identity. Anonymous browsing enhances privacy and anonymity when accessing the internet.
• Improved network performance. Proxy servers enhance network performance by locally caching copies of popular websites. This caching speeds up access to frequently visited sites, reduces bandwidth usage and ultimately improves overall network performance.
• No regional restrictions or blocks. By using a proxy server to change their IP address, individuals can bypass geographical content restrictions. The masked IP address makes them appear as though they're accessing content from a region where access is permitted. This enables them to access websites, services or content that might otherwise be restricted based on their location.

Types of proxy servers

Proxy servers come in various types, each serving specific purposes and offering distinct functionalities. The following are some common types of proxy servers:

Forward proxies

Forward proxies send the requests of a client onward to a web server. Users access forward proxies by directly surfing to a web proxy address or by configuring their internet settings. Forward proxies enable users to circumvent firewalls and increase their privacy and security, but can sometimes be used to download illegal content such as copyrighted works or child sexual abuse material.

Reverse proxies

Reverse proxies transparently handle all requests for resources on destination servers without requiring any action from the requester or the origin server. Reverse proxies are used to do the following:

• Enable indirect access when a website disallows direct connections as a security measure.
• Enable load balancing between servers.
• Stream internal content to internet users.
• Disable access to a site; for example, when an internet service provider (ISP) or government wishes to block a website.

Sites might be blocked for legitimate reasons. Sometimes these reasons are considered justifiable, and sometimes they aren't. Reverse proxies sometimes prevent access to news sites where users could view leaked information. They can also prevent end users from accessing sites where they can disclose information about government or industry actions.

Transparent proxies

Transparent proxies are typically found near the exit of a corporate network. These proxies centralize network traffic. On corporate networks, a proxy server is associated with -- or is part of -- a gateway server that separates the network from external networks -- typically the internet -- and a firewall that protects the network from outside intrusion and enables data to be scanned for security purposes before delivery to a client on the network.

These proxies help with monitoring and administering network traffic, as the computers in a corporate network are usually safe devices that don't need anonymity for typically mundane tasks.

Anonymous proxies

Anonymous proxy servers hide the IP address of the client using them to enable access to materials that are blocked by firewalls or to circumvent proxy IP address bans. They can also be used for enhanced privacy and protection from cyberattacks.

Highly anonymous proxies

Highly anonymous proxies hide even the fact that they're being used by clients and present a nonproxy public IP address. So not only do they hide the IP address of the client using them, high anonymity proxy servers also enable access to sites that might block proxy servers.

Socks 4 and 5 proxies

Socks 4 and 5 proxies provide proxy service for User Datagram Protocol data and Domain Name System (DNS) lookup operations in addition to web traffic. Some proxy servers offer both Socks protocols.

DNS proxies

DNS proxies forward DNS requests from local area networks to internet DNS servers while caching for enhanced speed.

Distorting proxies

A distorting proxy is a type of proxy server that masks the client's IP address by modifying the HTTP headers and presenting a fake IP address to the target server.

This manipulation creates the impression that the user is from a different location, providing a layer of anonymity and privacy while limiting the ability to monitor the user's browsing activity.

HTTP proxies

Primarily used for web browsing, an HTTP proxy handles HTTP requests from web browsers and forwards them to web servers. It can also handle HTTPS requests in some cases.

Residential and data center proxies

Residential and data center proxies conceal the real IP addresses of the client, with the primary distinction lying in their IP address sources. Data center proxies originate from data centers, whereas ISPs assign residential proxies.

Proxy hacking

In proxy hacking, an attacker attempts to steal hits from an authentic webpage in a search engine's index and search results pages. The proxy hacker has either a fraudulent site emulating the original or whatever they choose to show the clients requesting the page.

Proxy hacking encompasses a range of activities, including the following:

• Imitation website creation. The attacker creates a copy of the targeted webpage on a proxy server and uses methods such as keyword stuffing and linking to the copied page from external sites to artificially raise its search engine ranking. The authentic page will rank lower and can be seen as duplicated content, in which case a search engine can remove it from its index.
• Redirection and malware introduction. Proxy hacking can also be used to deliver pages with malicious intent. Proxy hacking can direct users to fake banking sites, for example, to steal account info that can then be sold or used to steal funds from the account. The attacker can also use the hack to direct users to a malware-infected site to compromise their machines for a variety of nefarious purposes.
• Search engine optimization hijacking and content scraping. SEO hijacking involves attempting to gain an advantage over competitors or redirecting traffic to fraudulent websites for advertising revenue. It's also known as content scraping or page hijacking.
• Application-level hijacking. In this type of proxy hacking, users exploit vulnerabilities in web applications that don't use SSL to encrypt data. This involves modifying traffic and information sent to a trusted application, pretending the traffic came from a legitimate user.

Some means have been developed to compromise proxy abilities. Specially crafted Adobe Flash and Java apps, JavaScript, ActiveX and some other browser plugins can be used to reveal a proxy user's identity, so proxies shouldn't be used on untrusted sites or anywhere that anonymity is important.

Website owners who suspect they've been the victim of a proxy hack can test the theory by searching for a phrase that would be almost uniquely identifying to the site. Their site should be prominent on the search engine results page. If a second site with the same content shows up, it might be a proxy page.

Proxy server security

Proxy servers in many forms enhance security, but they can also be vulnerable themselves. To prevent denial-of-service (DoS) attacks and network intrusion, administrators should take the following steps:

• Keep software up to date. Software updates often include patches that address security vulnerabilities discovered in previous versions. By regularly updating the proxy server software, administrators can mitigate the risk of exploitation by malicious actors who target known vulnerabilities. Updates also introduce new security features or improvements to existing security mechanisms. These enhancements can strengthen the proxy server's defenses against evolving threats such as malware, phishing attacks and unauthorized access attempts.
• Use load balancing. Load balancing distributes incoming traffic across multiple proxy servers. For example, if one server becomes unavailable due to a security incident or overload, the load balancer redirects traffic to other servers. This ensures continuous availability and minimizes the effects of potential attacks or failures.
• Enforce secure authorization and authentication. Secure authorization and authentication measures ensure only authorized users and devices can access the proxy server. For example, the server can verify their identity before granting access by requiring users to authenticate with strong credentials such as passwords, biometrics or two-factor authentication.
• Block unsolicited traffic and audit proxy activities. Blocking unsolicited proxy traffic and regularly monitoring and auditing proxy activities can help detect and prevent security breaches such as DoS attacks, malware and phishing attempts. This enables administrators to promptly identify unusual traffic patterns, unauthorized access attempts and other suspicious activities.
• Define and enforce access policies. Defining and enforcing access policies that dictate which websites or services users can access through the proxy server can minimize the risk of malicious activities. These policies restrict user access to only authorized websites and services, reducing exposure to malicious content and unauthorized activities. By controlling access, organizations can prevent data exfiltration attempts and ensure compliance with regulatory standards.
• Disable or remove unnecessary services, ports or features. By eliminating or disabling unused functionalities, administrators can minimize potential entry points that attackers could exploit. This proactive approach minimizes the attack surface and reduces the complexity of the server environment, making it easier to manage and secure. It also decreases the likelihood of vulnerabilities in unused services or ports that could otherwise be targeted for unauthorized access or exploitation.
• Set up a backup strategy. Setting up a backup strategy for critical proxy server configurations and data ensures quick recovery in case of a security incident or hardware failure. It can also help protect against certain cyberextortion attempts such as ransomware attacks. For example, ransomware attacks can encrypt or delete data, including proxy server configurations and logs. Having offline backups stored securely ensures organizations can recover their systems without paying ransom demands, thereby mitigating financial risks associated with cyberextortion.

Proxy server vs. VPN

The choice between a proxy server and a virtual private network depends on the specific security and privacy needs of the user or organization. The main differences between a VPN and a proxy server include the following:

Proxy server

• Proxy servers function as an agent between a user and the internet. While they hide the user's IP address from the web server being accessed, proxy servers don't secure the data being sent and received.
• Because proxy servers don't encrypt data, a user's online activities aren't fully protected when using a proxy server.
• The scope of protection of a proxy server is typically limited, since it only functions with a single app or service.
• Free proxy connections can be slower and less secure due to fewer configuration options and reduced infrastructure.

VPN server

• A VPN server encrypts and routes all internet traffic through a remote server. This provides a high level of security and privacy for users' online activities.
• VPNs also hide the user's IP address, but they go further and protect privacy by redirecting internet data through an encrypted tunnel.
• VPNs offer comprehensive protection by securing all internet traffic, not just specific apps or services.
• While both VPNs and proxy servers can slow down browsing, VPNs are generally considered the faster option, especially when compared with free proxy connections.

Forward and reverse proxies secure and isolate private network resources, each serving distinct roles in modern enterprise architectures. Understand their differences for effective deployment and management.