We know how easy it is to get caught up in shipping features and forget about the quiet gaps that can turn into security nightmares. With ASP.NET Core, the pressure’s always on—deadlines, user requests, and the next big thing.
But if we don’t pay attention, attackers find those small oversights. That’s why we put together a checklist that’s clear and direct. We focus on the basics: forcing HTTPS, locking down cookies, handling errors the right way, and keeping our codebase fresh. It’s about building apps that hold up, even when someone’s trying to break in.
Key Takeaway
- Enforce HTTPS and secure headers to protect data in transit and control browser behavior.
- Validate inputs, use anti-forgery tokens, and implement strong authentication to block common attacks.
- Keep dependencies updated and monitor logs to catch vulnerabilities early and respond effectively.
Enforce HTTPS Everywhere
We never skip HTTPS. Not once. Every bit of data flying between a browser and our app needs protection, or we’re just begging for someone to listen in. Plain HTTP is like shouting passwords across a crowded street—someone’s gonna hear. So we toss in app.UseHttpsRedirection() early in the pipeline. Not middle. Not later. Right near the start. (1)
HTTP Strict Transport Security (HSTS)
There’s something reassuring about knowing the browser won’t even try to reach us over HTTP again. HSTS does that. We set it up so the browser remembers—only HTTPS, no exceptions. We usually start with something like 30 days (max-age=2592000) while testing, then crank it up once we’re confident.
Practical Tip
We test our HTTPS setup using online TLS testers—those tools don’t lie. They’ll point out weak ciphers or half-baked certificates. Worth the ten minutes.
Input Validation: Guarding Against Injection Attacks
We treat every piece of user input like it’s wrapped in barbed wire. Feels harsh, maybe, but it keeps us honest. We’ve had forms that seemed harmless until a stray SQL statement sneaked in. Now, we use [Required], [StringLength], and regex attributes without blinking.
Server-Side Validation
We don’t trust JavaScript to catch bad input. It’s nice, sure. But server-side is where the line gets drawn. If it doesn’t pass on the backend, it doesn’t get in—simple as that.
Output Encoding
When we display user input, we let Razor do the work. It’s already set up to HTML-encode everything. Still, whenever we have to output raw HTML (and sometimes we have to), we double-check it six ways from Sunday.
Practical Tip
If we’re writing SQL by hand, we stop. ORM tools like EF Core aren’t perfect, but they build queries with parameters—and that helps. We’ve avoided more than a few headaches by refusing to concatenate strings directly.
Authentication and Authorization: Controlling Access
Every user’s action starts with a question: “Who are you, and what can you do?” That’s the heart of it. Our identity system answers that with solid password rules, two-factor options, and role checks that don’t feel like duct tape.
Strong Password Policies
We don’t accept “123456.” Ever. We ask for length, mix of characters, and lock accounts after 5 bad tries. Keeps the bots sweating.
Multi-Factor Authentication (MFA)
MFA saves us every time someone reuses a leaked password. We like simple app-based codes—SMS feels too easy to intercept.
Role-Based Access Control (RBAC)
Our app knows who’s an admin, who’s a user, and who just signed up yesterday. Roles live in one place. It’s easier to manage and harder to mess up.
Token-Based Authentication and JWT Security
For APIs, we use JWTs. They’re fast and stateless. But we sign them tight, expire them fast, and keep them small. No personal info. No secrets inside.
Practical Tip
Every couple months, we audit our roles. Some users outgrow their access. Others shouldn’t have had it to begin with. A quick cleanup goes a long way.
Data Protection: Safeguarding Sensitive Information
We don’t just store data—we guard it. Things like tokens, cookies, even user preferences—if it’s sensitive, we encrypt it with the Data Protection API.
Key Management
We stash our keys where they can’t be touched by the app’s file system. Cloud key services help here, but we’ve also used environment-level secrets.
Encryption at Rest and In Transit
Our rule: if it’s personal or private, it’s encrypted. On disk. In transit. Doesn’t matter. Full TLS on everything, and encrypted DB fields when needed.
Practical Tip
We rotate our keys yearly, minimum. And we test our recovery steps twice—once when things are calm, once during chaos (because that’s when it matters most).
Secure Cookies: Protecting Sessions
Cookies feel harmless. They aren’t. We’ve seen sessions stolen by one bad config. Now we set Secure, HttpOnly, and SameSite by default. Every time.
Cookie Flags
- Secure — HTTPS only
- HttpOnly — no JavaScript access
- SameSite=Strict or Lax — stops cross-site weirdness
Session Management
Our sessions expire after 20 minutes of inactivity. Tokens refresh silently, but nothing lasts forever. That’s how we keep stale sessions from becoming attack surfaces.
Practical Tip
We crack open the browser dev tools after every deployment. A fast check on cookie settings saves hours of debugging later.
Cross-Site Request Forgery (CSRF) Protection
CSRF is sneaky. We’ve seen it turn a harmless form into a trojan horse. That’s why we lean on [ValidateAntiForgeryToken] for every POST form. Razor helps here—it adds the hidden token automatically.
Anti-Forgery Tokens
The anti-forgery token checks two things: does the token match what the server expects, and did it come from the right origin? Both matter. Without both, it’s useless.
Practical Tip
APIs don’t use cookies often, but if they do, we switch to custom headers or OAuth tokens to keep CSRF out.
Content Security Policy (CSP): Limiting What Runs
We’ve stopped a lot of XSS junk just by using a decent CSP. Feels like a small thing, but blocking script tags from shady origins? That alone buys peace of mind.
Implementing CSP
Our policies usually allow scripts and styles from our own domain, maybe a CDN or two. We start with report-only mode, then go full-enforce once things look clean.
Practical Tip
We watch our CSP violation reports weekly. It’s boring—until it isn’t. One weird script trying to load from a random subdomain is all it takes to start digging.
Error Handling: Avoiding Information Leakage
When something breaks, users shouldn’t see stack traces. They need something calm. Clean. We give them that. And meanwhile, we log the dirty details safely.
Custom Error Pages
Our 500 page doesn’t say “NullReferenceException.” It says “Oops.” We keep it vague. Our logs handle the specifics.
Logging Sensitive Data
We log request paths, response times, status codes. But never passwords, credit cards, or tokens. Not even for a second.
Practical Tip
Our dev and prod error settings are miles apart. In dev, we show all the gory details. In prod, we don’t.
Database Security: Preventing SQL Injection and Unauthorized Access
SQL injection isn’t just theory. We’ve seen it ruin systems. That’s why we use EF Core or parameterized queries, no exceptions.
Principle of Least Privilege
Our DB user can only read and write what it must. No drop tables. No schema changes. Nothing fancy.
Practical Tip
Once a quarter, we scan database permissions. Sometimes, things creep in. Old test accounts. Forgotten roles. We clean house.
Secure Headers: Controlling Browser Behavior
Headers are like road signs. We use them to keep browsers on the safe path.
Common Security Headers
- X-Content-Type-Options: nosniff
- X-Frame-Options: DENY
- Strict-Transport-Security
- X-XSS-Protection (yeah, even if it’s mostly legacy)
Practical Tip
Middleware handles this fast. We plug it into the pipeline and forget about it—until something changes, and we have to tweak a setting.
Rate Limiting: Thwarting Brute-Force and DDoS
No one types a password 500 times in a minute. Bots do. We limit requests—logins especially—to slow down attackers. (2)
Implementing Rate Limits
We throttle by IP. Then by user. Sometimes by path. We return 429s when things get fishy.
Practical Tip
Rate limits are useless without lockouts. We combine both. One slows them down, the other shuts the door.
Logging and Monitoring: Detecting Suspicious Activity
Our logs have caught stuff we didn’t even know was happening. Failed logins, token replays, odd request patterns—they all leave a trail.
What to Log
- Authentication failures
- Access denials
- Unusual IP addresses
- Sudden spikes in traffic
Avoid Logging
- Passwords
- Personal identifiers
- Raw request bodies (unless sanitized)
Practical Tip
Our logs pipe into a central system with alerts. We don’t watch them every second, but the system does.
Dependency and Patch Management: Staying Ahead of Vulnerabilities
Old packages carry ghosts. We patch often. Weekly usually. Sometimes more.
Regular Updates
We update everything—from ASP.NET Core itself to that one weird JSON parser we forgot we used.
Vulnerability Scanning
Automated tools scan our dependencies after every push. They flag CVEs and nudge us to fix them.
Practical Tip
CI/CD pipelines do the heavy lifting. We just read the reports—and fix what’s broken.
Secure File Uploads: Preventing Malicious Content
File uploads scare us more than most features. We treat every file like it’s dangerous until proven otherwise.
Validation and Scanning
We check file types, file sizes, and use antivirus scanning before we store anything.
Storage
We drop files outside the web root. They can’t be executed. They can’t be browsed directly.
Practical Tip
We rename uploads using GUIDs. Keeps things clean. No clashes. No hints about what’s inside.
Secure Configuration and Environment Management
Secrets don’t belong in source code. Ever. We store them where the app can reach them, but the repo can’t.
Use Environment Variables
Every connection string, API key, or token lives in the environment. Local or cloud, doesn’t matter.
Secure App Secrets
During dev, we use secret managers. In prod, we move to managed services with audit logs.
Practical Tip
We grep our repo for strings like password= or apikey: before every release. Catches stuff we didn’t mean to commit.
Secure Deployment and DevOps Practices
Security doesn’t stop with code. It follows us through the build, deploy, and monitor phases too.
Secure Middleware and Routing
Middleware order matters. We test it. One misplaced auth check and the whole app’s exposed.
Secure DevOps
Our pipelines run security checks: static analysis, dependency scanning, basic vulnerability probes. It’s noisy sometimes, but we’d rather filter noise than miss a breach.
Practical Tip
We run a pentest twice a year—internally if we have to. The results always sting, but they help.
FAQ
What are the most important security steps every ASP.NET Core developer should follow?
Start with authentication and authorization to control who can access your app. Always use HTTPS to protect data in transit. Keep your packages updated, validate all user input, and store secrets properly. These basic steps prevent most common attacks and keep your application safe from hackers.
How do I protect my ASP.NET Core app from hackers trying to steal user data?
Use strong authentication methods and encrypt sensitive information. Set up proper authorization rules so users only see what they should. Always validate data that comes from users before processing it. Store passwords securely using built-in hashing tools, and never put secret keys directly in your code.
Why should I use HTTPS everywhere in my ASP.NET Core application?
HTTPS encrypts all data traveling between your app and users’ browsers. Without it, hackers can easily read passwords, personal information, and other sensitive data. Modern browsers also warn users about unsafe sites, which hurts your reputation. Always redirect HTTP traffic to HTTPS automatically.
What’s the easiest way to handle user passwords safely in ASP.NET Core?
Never store passwords as plain text. Use the built-in Identity system which automatically hashes passwords properly. Require strong passwords with numbers, letters, and symbols. Add two-factor authentication for extra protection. Let users reset passwords securely through email, and consider using external login providers when possible.
How do I keep hackers from injecting bad code into my ASP.NET Core app?
Always validate and clean user input before using it. Use parameterized queries for database operations instead of building SQL strings directly. The framework helps prevent many injection attacks automatically, but you still need to be careful with user data and avoid executing untrusted code.
Where should I store API keys and database passwords in ASP.NET Core?
Never put secrets directly in your code or config files. Use the Secret Manager for development and secure key vaults for production. Environment variables work too, but make sure they’re properly protected. Keep different secrets for development, testing, and live environments to limit damage if one gets compromised.
How often should I update my ASP.NET Core packages and dependencies?
Check for security updates at least monthly, but apply critical security patches immediately. Subscribe to security announcements and use tools that scan for vulnerable packages. Keep both the framework and third-party libraries current, as outdated components are common entry points for attackers.
What logging should I set up to catch security problems in my ASP.NET Core app?
Log all authentication attempts, authorization failures, and suspicious activities. Track unusual patterns like multiple failed logins or attempts to access restricted areas. Store logs securely and monitor them regularly. Good logging helps you spot attacks early and understand what happened during security incidents.
Conclusion
We don’t fix everything at once. We start with what’s most exposed—HTTPS, input validation, authentication. Then we work our way out. Security’s never really “done,” but each step buys peace of mind. Keeps the app standing when the wind hits hard. And that’s the goal. Something that lasts. Something that holds.
If you’re ready to take your secure coding skills to the next level, consider joining the Secure Coding Practices Bootcamp. This hands-on, real-world training is designed by experts to help developers build safer software from day one. Whether you’re part of a team or flying solo, it’s a practical way to level up your security game.
Related Articles
- https://securecodingpractices.com/secure-coding-in-c-net/
- https://securecodingpractices.com/prevent-sql-injection-ado-net-entity-framework/
- https://securecodingpractices.com/node-js-security-best-practices-checklist/
References
- https://learn.microsoft.com/en-us/aspnet/core/security/?view=aspnetcore-9.0
- https://learn.microsoft.com/en-us/aspnet/core/fundamentals/best-practices?view=aspnetcore-9.0
