Web

/kɔːrz/

n. “You may speak… but only from where I recognize you.”

CORS, short for Cross-Origin Resource Sharing, is a browser-enforced security model that controls how web pages are allowed to request resources from origins other than their own. It exists because the web learned, the hard way, that letting any site freely read responses from any other site was a catastrophically bad idea.

By default, browsers follow the same-origin policy. A script loaded from one origin — defined by scheme, host, and port — is not allowed to read responses from another. This rule prevents malicious websites from silently reading private data from places like banking portals, email providers, or internal dashboards. Without it, the browser would be an accomplice.

CORS is the controlled exception to that rule. It allows servers to explicitly declare which external origins are permitted to access their resources, and under what conditions. The browser enforces these declarations. The server does not trust the client. The client does not trust itself. The browser acts as the bouncer.

This control is expressed through HTTP response headers. When a browser makes a cross-origin request, it looks for permission signals in the response. If the headers say access is allowed, the browser hands the response to the requesting script. If not, the browser blocks it — even though the network request itself may have succeeded.

One of the most misunderstood aspects of CORS is that it is not a server-side security feature. Servers will happily send responses to anyone who asks. CORS determines whether the browser is allowed to expose that response to JavaScript. This distinction matters. CORS protects users, not servers.

Requests come in two broad flavors: simple and non-simple. Simple requests use safe HTTP methods and headers and are sent directly. Non-simple requests trigger a preflight — an automatic OPTIONS request sent by the browser to ask the server whether the real request is permitted. This preflight advertises the method and headers that will be used, and waits for approval.

The preflight mechanism exists to prevent side effects. Without it, a malicious page could trigger destructive actions on another origin using methods like PUT or DELETE without ever reading the response. CORS forces the server to opt in before the browser allows those requests to proceed.

Credentials complicate everything. Cookies, HTTP authentication, and client certificates are powerful — and dangerous. CORS requires explicit permission for credentialed requests, and forbids wildcard origins when credentials are involved. This prevents a server from accidentally granting authenticated access to the entire internet.

CORS is often confused with CSP, but they solve different problems. CSP restricts what a page is allowed to load or execute. CORS restricts what a page is allowed to read. One controls inbound behavior. The other controls outbound trust.

Many modern APIs exist entirely because of CORS. Without it, browser-based applications could not safely consume third-party services. With it, APIs can be shared selectively, documented clearly, and revoked instantly by changing headers rather than code.

CORS does not stop attackers from sending requests. It stops browsers from handing attackers the answers. In the security world, that distinction is everything.

When developers complain that CORS is “blocking their request,” what it is actually blocking is their assumption. The browser is asking a simple question: did the other side agree to this conversation? If the answer is no, the browser walks away.

CORS is not optional. It is the price of a web that allows interaction without surrendering isolation — and the reason your browser can talk to many places without betraying you to all of them.

/ˌsiː-ɛs-ˈpiː/

n. “Trust nothing by default. Especially the browser.”

CSP, short for Content Security Policy, is a defensive security mechanism built into modern browsers to reduce the damage caused by malicious or unintended content execution. It does not fix broken code. It does not sanitize input. What it does instead is draw very explicit boundaries around what a web page is allowed to load, execute, embed, or communicate with — and then enforces those boundaries with extreme prejudice.

At its core, CSP is a browser-enforced rulebook delivered by a server, usually via HTTP headers, sometimes via meta tags. That rulebook answers questions browsers used to shrug at: Where can scripts come from? Are inline scripts allowed? Can this page embed frames? Can it talk to third-party APIs? If an instruction isn’t explicitly allowed, it is blocked. Silence becomes denial.

The policy exists largely because of XSS. Cross-site scripting thrives in environments where browsers eagerly execute whatever JavaScript they encounter. For years, the web operated on a naive assumption: if the server sent it, the browser should probably run it. CSP replaces that assumption with a whitelist model. Scripts must come from approved origins. Stylesheets must come from approved origins. Inline execution becomes suspicious by default.

This matters because many real-world attacks don’t inject entire applications — they inject tiny fragments. A single inline script. A rogue image tag with an onerror handler. A compromised third-party analytics file. With CSP enabled and properly configured, those fragments simply fail to execute. The browser refuses them before your application logic ever sees the mess.

CSP is especially effective when paired with modern authentication and session handling. Even if an attacker manages to reflect or store malicious input, the policy can prevent that payload from loading external scripts, exfiltrating data, or escalating its reach. This makes CSP one of the few mitigations that still holds value when other layers have already failed.

Policies are expressed through directives. These directives describe allowed sources for different content types: scripts, styles, images, fonts, connections, frames, workers, and more. A policy might state that scripts are only allowed from the same origin, that images may load from a CDN, and that inline scripts are forbidden entirely. Browsers enforce each rule independently, creating a layered denial system rather than a single brittle gate.

Importantly, CSP can operate in reporting mode. This allows a site to observe violations without enforcing them, collecting reports about what would have been blocked. This feature turns deployment into a learning process rather than a blind leap. Teams can tune policies gradually, tightening restrictions as they understand their own dependency graph.

CSP does not replace input validation. It does not replace output encoding. It does not make unsafe frameworks safe. What it does is drastically limit the blast radius when something slips through. In that sense, it behaves more like a containment field than a shield — assuming compromise will happen, then making that compromise far less useful.

Modern frameworks and platforms increasingly assume the presence of CSP. Applications built with strict policies tend to avoid inline scripts, favor explicit imports, and document their dependencies more clearly. This side effect alone often leads to cleaner architectures and fewer accidental couplings.

CSP is not magic. Misconfigured policies can break applications. Overly permissive policies can provide a false sense of safety. But when treated as a first-class security control — alongside transport protections like TLS and authentication mechanisms — it becomes one of the most effective browser-side defenses available.

In a hostile web, CSP doesn’t ask whether content is trustworthy. It asks whether it was invited. Anything else stays outside.

/ˈæŋɡjələr/

n. “A framework that turns complexity into structured interactivity.”

Angular is a TypeScript-based front-end web application framework developed and maintained by Google. It allows developers to build dynamic, single-page applications (SPAs) using a component-driven architecture, reactive programming patterns, and declarative templates. Unlike libraries such as React, which focus on the view layer, Angular provides a complete ecosystem, including routing, forms, HTTP services, and dependency injection.

One of the hallmark features of Angular is its declarative templates. Developers write HTML enhanced with Angular-specific syntax, such as *directives* and *bindings*, to express how the UI should react to changes in data. The framework then automatically updates the DOM, reflecting state changes without manual intervention.

Example: A shopping cart component can display items, update totals, and enable checkout without ever directly manipulating the DOM. Angular’s data binding ensures that any change in the underlying data model instantly reflects in the UI.

Angular leverages a powerful dependency injection system, which promotes modularity and testability. Services, such as HTTP clients or logging utilities, can be injected into components without manually instantiating them. This pattern encourages separation of concerns and reduces boilerplate code.

The framework also integrates reactive programming through RxJS, allowing developers to manage asynchronous data streams with observables. This is particularly useful for applications that rely on real-time updates, such as messaging platforms or dashboards.

Performance optimizations in Angular include Ahead-of-Time (AOT) compilation, tree-shaking, and lazy loading. AOT compiles templates at build time, reducing runtime parsing and increasing load speed. Lazy loading allows modules to load only when required, improving initial render performance.

Angular is widely used in enterprise environments, where maintainability, scalability, and strong typing (via TypeScript) are priorities. It pairs effectively with REST APIs, GraphQL, and modern authentication methods like OAuth and SSO.

Security is also a built-in consideration: Angular automatically sanitizes content in templates to prevent XSS attacks, and developers are encouraged to follow best practices for authentication and authorization.

In essence, Angular is a full-featured, structured framework that allows developers to build complex, responsive, and maintainable web applications while handling state, UI updates, and performance optimizations out-of-the-box.

/nɛkst dʒeɪ ɛs/

n. “The framework that makes React feel like magic.”

Next.js is a React-based framework designed to simplify building fast, scalable, and production-ready web applications. It extends React by providing built-in server-side rendering (SSR), static site generation (SSG), routing, and API routes — features that normally require additional configuration or libraries.

At its core, Next.js treats every file in the pages directory as a route. A pages/index.js file becomes the root path, pages/about.js becomes /about, and so on. This filesystem-based routing eliminates the need for manual route definitions, making development more intuitive.

One of the major strengths of Next.js is server-side rendering. Instead of sending a blank HTML shell to the browser and letting JavaScript populate content, Next.js can pre-render pages on the server, delivering fully formed HTML. This improves SEO, performance, and perceived load times. Developers can also opt for static generation, where pages are built at build time and served as static assets.

Example: An e-commerce product page can be statically generated for each product, ensuring fast load times and search engine discoverability. At the same time, dynamic data like user-specific recommendations can be fetched client-side or via server-side functions.

Next.js also supports API routes, allowing developers to create backend endpoints within the same project. A file in pages/api/hello.js becomes an HTTP endpoint at /api/hello, removing the need for a separate server just to handle basic API functionality.

Performance optimizations are baked in: automatic code splitting ensures users only download the JavaScript they need, and built-in image optimization improves rendering efficiency. It works seamlessly with modern standards like TLS and HTTPS, making production deployments secure by default.

The framework integrates well with state management libraries such as Redux or React Query, and supports both TypeScript and JavaScript. This flexibility allows teams to scale projects from small static sites to complex enterprise applications while keeping the development workflow consistent.

Security, SEO, and user experience are core considerations in Next.js. By handling server-side rendering, static generation, and routing intelligently, it reduces attack surfaces, ensures content is discoverable, and delivers smooth, responsive interfaces.

In essence, Next.js turns React applications into production-ready, fast, and SEO-friendly sites without the friction of custom configuration, making it a favorite for developers who want both control and efficiency.

/riˈækt/

n. “A library that thinks fast and renders faster.”

React is a JavaScript library for building user interfaces, primarily for web applications. Created by Facebook, it allows developers to design complex, interactive UIs by breaking them down into reusable components. Each component manages its own state and renders efficiently when that state changes, providing a reactive user experience.

At the core of React is the concept of a virtual DOM. Rather than directly manipulating the browser’s DOM, React maintains a lightweight copy of the DOM in memory. When a component’s state changes, React calculates the minimal set of changes needed to update the real DOM, reducing unnecessary reflows and improving performance.

Example: Suppose you have a comment section. Each comment is a React component. If a user edits one comment, only that component re-renders, not the entire list. This makes updates fast and predictable.

React uses a declarative syntax with JSX, which looks like HTML but allows embedding JavaScript expressions. Developers describe what the UI should look like for a given state, and React ensures the actual DOM matches that description. This approach contrasts with imperative DOM manipulation, making code easier to reason about and debug.

Beyond the core library, React has an ecosystem including React Router for navigation, Redux for state management, and Next.js for server-side rendering. These tools enable large-scale, maintainable applications while keeping components modular and testable.

Security and performance considerations are critical in React. Since React directly interacts with the DOM, improper handling of untrusted input can lead to XSS vulnerabilities. Additionally, developers must manage state and props efficiently to avoid unnecessary renders and memory leaks.

In essence, React is not just a library; it is a methodology for building modern, component-driven web applications that are fast, predictable, and maintainable. Its declarative, reactive nature has influenced countless frameworks and continues to shape how developers approach UI development.

/ˈdiː-ˈoʊ-ˈɛm/

n. “Where the browser meets your code.”

DOM, short for Document Object Model, is a programming interface for HTML and XML documents. It represents the page so scripts can change the document structure, style, and content dynamically. Think of it as a live map of the web page: every element, attribute, and text node is a node in this tree-like structure that can be accessed and manipulated.

When a browser loads a page, it parses the HTML into the DOM. JavaScript can then traverse this structure to read or modify elements. For instance, you can change the text of a paragraph, add a new image, or remove a button — all without reloading the page. This dynamic interaction is the foundation of modern web applications and frameworks.

The DOM treats documents as a hierarchy: the document is the root node, containing elements, attributes, and text nodes. Each element is a branch, each text or attribute a leaf. Scripts use APIs such as getElementById, querySelector, or createElement to navigate, modify, or create new nodes. Events, like clicks or key presses, bubble through this tree, allowing developers to respond to user interaction.

Example: Clicking a button might trigger JavaScript that locates a div via the DOM and updates its content. Frameworks like React or Angular build virtual DOMs to efficiently update the visible DOM without unnecessary reflows or repaints, improving performance.

Beyond HTML, the DOM is standardized by the W3C, ensuring consistency across browsers. This makes cross-browser scripting feasible, even if implementations vary slightly. Security considerations are tied closely to the DOM: XSS attacks exploit the ability to inject malicious scripts into the document tree, showing how central the DOM is to web security.

In essence, the DOM is the living interface between static markup and dynamic behavior. It enables scripts to read, modify, and react to the document, forming the backbone of interactive, responsive, and modern web experiences.

/ˌɛks-ɛs-ˈɛs/

n. “Sneaky scripts slipping where they shouldn’t.”

XSS, short for Cross-Site Scripting, is a class of web security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. Unlike server-side attacks, XSS exploits the trust a user has in a website, executing code in their browser without their consent or knowledge.

There are three main types of XSS: Reflected, Stored, and DOM-based. Reflected XSS occurs when malicious input is immediately echoed by a web page, such as through a search query or URL parameter. Stored XSS involves the attacker saving the payload in a database or message forum so it executes for anyone viewing that content. DOM-based XSS happens when client-side JavaScript processes untrusted data without proper validation.

A classic example: a user clicks on a seemingly normal link that contains JavaScript in the query string. If the website fails to sanitize or escape the input, the script runs in the victim’s browser, potentially stealing cookies, session tokens, or manipulating the page content. XSS attacks can escalate into full account takeover, phishing, or delivering malware.

Preventing XSS relies on a combination of techniques: input validation, output encoding, and content security policies. Frameworks often include built-in escaping functions to ensure that user input does not become executable code. For example, in HTML, characters like < and > are encoded to prevent interpretation as tags. In modern web development, using libraries that automatically sanitize data, alongside Content Security Policy, greatly reduces risk.

XSS remains one of the most common vulnerabilities in web applications, making awareness critical. Even large, popular sites can fall victim if validation and sanitization practices are inconsistent. Testing tools, such as automated scanners, penetration tests, and bug bounty programs, often prioritize XSS detection due to its prevalence and impact.

In essence, XSS is about trust and control. Users trust a website to deliver content safely; attackers exploit that trust to execute unauthorized scripts. Proper sanitization, rigorous coding practices, and security policies are the antidotes, turning a website from a potential playground for malicious scripts into a secure, trustworthy environment.

/ˈdʌbəljuː-ˈeɪ-ɛf/

n. “A gatekeeper that filters the bad, lets the good pass, and occasionally throws tantrums.”

WAF, short for Web Application Firewall, is a specialized security system designed to monitor, filter, and block HTTP traffic to and from a web application. Unlike traditional network firewalls that focus on ports and protocols, a WAF operates at the application layer, understanding web-specific threats like SQL injection, cross-site scripting (XSS), and other attacks targeting the logic of web applications.

A WAF sits between the client and the server, inspecting requests and responses. It applies a set of rules or signatures to detect malicious activity and can respond in several ways: block the request, challenge the client with a CAPTCHA, log the attempt, or even modify the request to neutralize threats. Modern WAF solutions often include learning algorithms to adapt to the traffic patterns of the specific application they protect.

Consider an example: a user submits a form on a website. Without a WAF, an attacker could inject SQL commands into input fields, potentially exposing databases. With a WAF, the request is inspected, recognized as suspicious, and blocked before it reaches the backend, preventing exploitation.

WAFs can be deployed as hardware appliances, software running on a server, or cloud-based services. Popular cloud-based offerings integrate seamlessly with CDNs and CDN services, combining traffic acceleration with security filtering. Rulesets may follow well-known standards, such as the OWASP Top Ten, ensuring coverage against the most common web vulnerabilities.

While a WAF provides strong protection, it is not a panacea. It cannot fix insecure code or prevent all attacks, especially those that exploit logical flaws not covered by its rules. However, combined with secure coding practices, HTTPS, proper authentication mechanisms like OAuth or SSO, and monitoring, a WAF significantly raises the bar for attackers.

Modern WAF features often include rate limiting, bot management, and integration with SIEM systems, providing visibility and automated response to threats. They are particularly valuable for high-traffic applications or services exposed to the public internet, where the volume and diversity of requests make manual inspection impossible.

In short, a WAF is a critical component in web application security: it enforces rules, blocks known attack patterns, and adds a layer of defense to protect sensitive data, infrastructure, and user trust. It does not replace secure design but complements it, catching threats that slip past traditional defenses.

/ˌeɪtʃ-tiː-ɛs-tiː-ɛs/

n. “Never talk unencrypted, even if asked nicely.”

HSTS, short for HTTP Strict Transport Security, is a web security policy mechanism that tells browsers to always use HTTPS when communicating with a specific site. Once a browser sees the HSTS header from a site, it refuses to make any unencrypted HTTP requests for that domain, effectively preventing downgrade attacks and certain types of man-in-the-middle attacks.

Introduced in 2012, HSTS is a response to the persistent problem of users accidentally navigating to HTTP versions of sites or attackers attempting to intercept HTTP traffic and redirect users to malicious endpoints. By enforcing HTTPS strictly, HSTS removes that human and technical error vector.

The policy is communicated via a special response header: Strict-Transport-Security. A typical header might look like this: Strict-Transport-Security: max-age=31536000; includeSubDomains; preload. This tells the browser to enforce HTTPS for one year, apply it to all subdomains, and optionally include the domain in browser preload lists.

For practical purposes, HSTS ensures that once a user visits a site securely, every subsequent visit—even if they type "http://" or click an outdated link—will automatically upgrade to HTTPS. This eliminates the chance of insecure communication slipping in and protects sensitive data like passwords, session cookies, and personal information.

Sites like online banking, e-commerce platforms, and cloud services often implement HSTS in combination with TLS to maximize security. It works hand-in-hand with HTTPS, certificate validation, and other transport-layer security mechanisms.

A subtle but important feature is HSTS preload. Maintained by browsers, this list allows domains to be hardcoded as HTTPS-only, preventing the first connection from ever occurring over HTTP. Domains must meet specific criteria—valid certificates, redirect from HTTP to HTTPS, and correct header configuration—to be added to this list safely.

Misconfiguration can backfire. If a domain deploys HSTS but later mismanages its certificates, users can be locked out because browsers refuse HTTP fallbacks. Planning, monitoring, and automation are crucial.

In short, HSTS enforces a strict policy: encrypted communication only, no exceptions, no shortcuts. It strengthens HTTPS adoption and ensures that even naive users remain protected against some of the most common web-layer attacks. Once deployed properly, it is a silent but formidable guardian of modern web security.

/ˌɛs-ɛf-ti-ˈpi/

n. “Securely moving files without looking over your shoulder.”

SFTP, short for SSH File Transfer Protocol or sometimes Secure File Transfer Protocol, is a network protocol that provides secure file transfer capabilities over the SSH (Secure Shell) protocol. Unlike traditional FTP, which sends data in plaintext, SFTP encrypts both commands and data, ensuring confidentiality, integrity, and authentication in transit.

Conceptually, SFTP looks like FTP: you can list directories, upload, download, delete files, and manage file permissions. But under the hood, all traffic is wrapped in an encrypted SSH session. This eliminates the need for separate encryption layers like FTPS while preventing eavesdropping and man-in-the-middle attacks.

A typical SFTP workflow involves connecting to a remote server with a username/password or SSH key, issuing commands like get, put, or ls, and transferring files through the secure channel. Clients like FileZilla, WinSCP, and command-line sftp utilities are commonly used to interact with SFTP servers.

SFTP is widely used for secure website deployment, backing up sensitive data, or exchanging large files between organizations. For example, a development team may deploy new web assets to a production server using SFTP, ensuring that credentials and content cannot be intercepted during transfer.

The protocol also supports advanced features like file permission management, resuming interrupted transfers, and atomic file operations. Because it operates over SSH, SFTP inherits strong cryptographic algorithms, including AES and HMAC, for encryption and authentication.

While SFTP is similar in appearance to FTP, it is a completely different protocol and is often preferred whenever security and compliance are concerns, such as for GDPR or CCPA regulated data transfers.

SFTP is not just FTP over SSH; it’s a purpose-built, secure protocol that keeps files safe in transit while offering the same flexibility that made FTP useful for decades.