Session Hijacking
Last updated: January 16, 2026
Session hijacking occurs when attackers obtain valid session tokens through theft, prediction, or fixation, allowing them to impersonate authenticated users.
Scan for This VulnerabilityWhat is Session Hijacking?
Once a user authenticates, applications issue session tokens (usually in cookies) to identify them. If an attacker obtains this token, they can make requests as that user. Tokens can be stolen via XSS, network interception, or exposed in logs/URLs.
Why It's Dangerous
This vulnerability can allow attackers to access sensitive data, compromise user accounts, or gain unauthorized control over your application. In AI-generated code, this issue is particularly common because security measures are often deprioritized in favor of rapid feature development.
Why AI Code Is Vulnerable
AI code generation tools focus on producing functional code quickly. They often generate patterns that work correctly but lack the defensive measures experienced security engineers would implement. This makes session hijacking particularly prevalent in vibe-coded applications.
Understanding the Technical Details
Session Hijacking is classified as a critical-severity vulnerability because of its potential to cause significant damage to your application and users. Understanding the technical mechanics helps you recognize and prevent this issue in your own code.
This vulnerability typically occurs when security controls are either missing entirely, improperly configured, or incorrectly implemented. In many cases, the code appears to work correctly during development and testing, but the security flaw becomes exploitable once the application is deployed and accessible to malicious actors.
Attackers actively scan for this type of vulnerability using automated tools. Once discovered, exploitation can be rapid—often within hours of your application going live. The consequences range from data theft and account takeover to complete system compromise depending on the application's architecture.
For vibe-coded applications built with platforms like Lovable, Bolt.new, Replit, or v0.dev, this vulnerability appears in roughly 20-40% of deployments according to security research. The AI-generated patterns often follow insecure defaults that require manual security hardening.
How It Happens
- Session tokens in URLs
- Missing HttpOnly cookie flag
- Missing Secure cookie flag
- XSS vulnerabilities enabling token theft
- Predictable session IDs
- Session fixation vulnerabilities
Impact
Complete account takeover
Access to all user data
Ability to perform actions as user
Persistent access until session expires
How to Detect
- Check cookie security attributes
- Verify session tokens aren't in URLs
- Test session ID randomness
- Look for XSS that could steal cookies
How to Fix
Secure cookie attributes
Use all protective cookie flags.
Set-Cookie: session=token; HttpOnly; Secure; SameSite=Lax; Path=/
// HttpOnly: Not accessible via JavaScript
// Secure: Only sent over HTTPS
// SameSite: Prevents CSRF
// Path: Limits cookie scopeRegenerate session on auth changes
Issue new session ID after login and privilege changes.
// After successful login
await session.regenerate();
// After privilege escalation
if (user.becameAdmin) {
await session.regenerate();
}Implement session timeout
Limit session lifetime and implement idle timeout.
// Session configuration
{
maxAge: 24 * 60 * 60 * 1000, // 24 hours absolute
rolling: true, // Extend on activity
idleTimeout: 30 * 60 * 1000, // 30 min idle
}Commonly Affected Platforms
Prevention Best Practices
The most effective approach to session hijacking is prevention. Implementing security measures during development is significantly easier and less costly than remediating vulnerabilities after deployment.
Security-First Development
When using AI code generation tools, always review the generated code for security implications. AI tools prioritize functionality over security, so treat all generated code as requiring security review. Establish a checklist of security requirements specific to your application type and verify each before deployment.
Continuous Security Testing
Integrate security scanning into your development workflow. Run scans after major code changes, before deployments, and on a regular schedule for production applications. Early detection of vulnerabilities reduces remediation costs and prevents potential breaches.
Defense in Depth
Never rely on a single security control. Implement multiple layers of protection so that if one control fails, others still protect your application. For example, combine authentication, authorization, input validation, and output encoding to create comprehensive protection against attacks.
Stay Informed
Security threats evolve constantly. Follow security researchers, subscribe to vulnerability databases, and monitor your dependencies for known issues. Understanding emerging threats helps you proactively protect your applications before attackers exploit new techniques.
Is Your App Vulnerable?
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Get Starter ScanFrequently Asked Questions
How does HttpOnly prevent session hijacking?
HttpOnly prevents JavaScript from accessing the cookie (document.cookie won't include it). This blocks XSS-based session theft - even if an attacker injects script, they can't read or exfiltrate the session cookie. Always use HttpOnly for session cookies.
What is session fixation?
Session fixation is when an attacker sets a known session ID before the user logs in, then uses that ID after authentication. Prevent it by regenerating the session ID upon login - invalidate the old session and issue a new one.