Web Security Basics Every Developer Must Know (2026)

Web Security Basics Every Developer Must Know (2026) Security isn't just for security teams. Every developer needs these fundamentals to protect their applications and users. The Threat Landscape in 2026 Most common attacks targeting web apps: 1. SQL Injection — Still #1, still devastating 2. XSS (Cross-Site Scripting) — Steals sessions, defaces sites 3. CSRF (Cross-Site Request Forgery) — Actions on behalf of users 4. Authentication bypass — Weak passwords, session fixation 5. Sensitive data exposure — API keys in code, unencrypted data 6. IDOR (Broken Access Control) — Accessing others' data 7. SSRF (Server-Side Request Forgery) — Internal network probing 8. Dependency vulnerabilities — Compromised npm/pip packages Key principle: Defense in depth → Don't rely on one security layer → Multiple independent controls → If one fails, others catch it #1 SQL Injection Prevention // ❌ VULNERABLE: String concatenation const query = `SELECT * FROM users WHERE email = ' ${ email } '` ; // Attacker inputs: ' OR '1'='1' -- // Result: Returns ALL users! // ✅ Parameterized queries (always!) const user = db . prepare ( ' SELECT * FROM users WHERE email = ? ' ). get ( email ); // The database treats the input as DATA, not code. // With ORM (Sequelize/TypeORM/Prisma): User . findOne ({ where : { email } }); // Safe by default // Even with parameterized queries, validate input first: function isValidEmail ( email ) { return /^ [^\s @ ] +@ [^\s @ ] + \.[^\s @ ] +$/ . test ( email ); } if ( ! isValidEmail ( email )) return res . status ( 400 ). json ({ error : ' Invalid email ' }); // ⚠️ Dangerous: Dynamic table/column names can't be parameterized! const allowedTables = [ ' users ' , ' products ' , ' orders ' ]; if ( ! allowedTables . includes ( table )) throw new Error ( ' Invalid table ' ); #2 XSS (Cross-Site Scripting) Defense // Types of XSS: // 1. Stored XSS: Malicious script saved in DB, shown to all viewers // → Comment sections, profiles, product reviews // 2. Reflected XSS: Sc