Web Application Attacks

When Sir Tim Berners-Lee released the first website in 1991, he surely didn’t foresee today’s sprawling web of dynamic applications powering banking, shopping, telemedicine, and even spaceflight dashboards. But along with this explosive growth has come an equally vibrant underground economy of attackers exploiting the very code that makes the modern web possible. Understanding how these attacks work is the first step toward building—and defending—resilient applications. Below we’ll explore the most prevalent web application attacks, real-world incidents that highlight their impact, and layered defenses your team can implement right away.

Injection Attacks

What they are.

Injection flaws occur when untrusted data is sent to an interpreter as part of a command or query. Classic examples include SQL, NoSQL, OS-command, and LDAP injection.

Why they matter.

In 2024, the MOVEit file-transfer breach exploited a SQL injection vulnerability and led to data theft from hundreds of organizations, costing an estimated ₹80,000 billion globally.

Defenses.

• Use parameterized queries or prepared statements in every data-store call.
• Employ rigorous input validation with allow-lists rather than block-lists.
• Deploy Web Application Firewalls (WAFs) that can flag anomalous query patterns.

Cross-Site Scripting (XSS)

What they are.

XSS lets attackers inject scripts into pages viewed by other users. Once executed, the script can hijack sessions, deface content, or redirect victims to phishing sites.

Real-world example.

In early 2025, a popular social network’s comment field failed to escape tags, leading to the automatic posting of credential-stealing links whenever users opened an infected thread.

Defenses.

• Encode output by context (HTML, JavaScript, CSS, URL).
• Implement a strong Content Security Policy (CSP).
• Use modern frameworks like React or Vue that auto-escape data bindings.

Cross-Site Request Forgery (CSRF)

What they are.

CSRF tricks authenticated users into submitting malicious requests—changing an email, initiating a funds transfer—without their knowledge.

Case in point.

A 2023 attack on a fintech startup used a hidden tag in a phishing email. When logged-in users opened the email, their browsers unknowingly sent a POST request that wired money to the attacker’s account.

Defenses.

• Include unpredictable CSRF tokens in state-changing requests.
• Use the SameSite cookie attribute (SameSite=Lax or Strict).
• Require re-authentication or multi-factor verification for critical actions.

Broken Authentication & Session Management

What they are.

Flaws that let attackers compromise passwords, keys, or session tokens.

Notable breach.

An e-commerce giant in 2024 leaked session IDs via a misconfigured analytics script. Attackers replayed the tokens to place fraudulent orders worth ₹16 million before detection.

Defenses.

• Store hashed and salted passwords with strong algorithms like Argon2id.
• Rotate session tokens on privilege change, logout, and password reset.
• Enable multi-factor authentication (MFA) for all accounts.

Security Misconfiguration

What they are.

Default credentials, verbose error messages, or unpatched CMS plugins all count as misconfigurations.

Example.

In 2023, a city’s online tax portal exposed stack traces in production, revealing the framework version; attackers used a known exploit to gain shell access.

Defenses.

• Follow Infrastructure as Code (IaC) with hardened baselines.
• Automate security scans in CI/CD pipelines.
• Enforce least privilege for containers, VMs, and serverless functions.

Sensitive Data Exposure

Sometimes listed as a consequence rather than a vector, data exposure often stems from weak crypto, improper key storage, or transmitting data over plaintext channels.

Solution stack.

• Use TLS 1.3 with HSTS; redirect HTTP to HTTPS at edge proxies.
• Encrypt data at rest with envelope encryption; store keys in a KMS.
• Apply field-level encryption for sensitive PII.

Insecure Deserialization

Objects serialized into JSON or binary blobs may be tampered with; when reconstituted, malicious payloads execute arbitrary code.

Defense.

Avoid native serialization of sensitive objects or use a strict allowlist of classes.

Server-Side Request Forgery (SSRF)

Attackers make your server fetch internal resources (IMDS, private APIs) that aren’t meant to be public.

Mitigations.

• Block direct IP or localhost calls unless explicitly required.
• Egress-filter outbound requests.
• Use metadata-proxy restrictions like IMDSv2 on AWS.

Zero-Day & Supply-Chain Attacks

Even dependency updates can be Trojan horses. The infamous Log4Shell vulnerability disclosed in December 2021—and still exploited in 2025—underscores how a single library can place thousands of services at risk.

What to do.

• Track SBOMs (Software Bills of Materials) for every build.
• Subscribe to vendor security advisories and patch within SLAs.
• Implement runtime application self-protection (RASP).

Defense-in-Depth: A Practical Blueprint

• Shift-Left Security: Integrate static application security testing (SAST) in pull-request workflows.
• Dynamic Testing: Run DAST scans against staging environments nightly.
• Runtime Protection: Use WAF, RASP, and anomaly detection tools.
• Culture & Training: Host secure-coding workshops and bug-bounty programs.
• Incident Response: Maintain runbooks and real-time SIEM alerting.

Key Takeaways

• Attack surfaces are expanding: APIs and SPAs introduce new vectors.
• Automation is essential: Toolchains must be integrated across the SDLC.
• People remain the strongest link: Educate and empower your dev teams.

Building bulletproof defenses isn’t a one-time sprint—it’s a continuous marathon. By understanding the mechanics of web application attacks and embedding security into every stage of development, you can stay several steps ahead of cyber-criminals and protect both your users and your brand.