Session Fixation

Summary

Session Fixation is a web application attack where an attacker tricks a user into using a known session ID, allowing the attacker to hijack the user’s authenticated session and gain unauthorized access.

Key Characteristics

• Exploits the session management mechanism by setting or forcing a session ID before user authentication.
• Allows attackers to take over a valid user session without needing to steal credentials.
• Commonly targets web applications that do not regenerate session IDs after login.
• Often involves sending a crafted URL or link containing the fixed session ID to the victim.
• Can lead to unauthorized access, data theft, and privilege escalation.

Defensive Controls

• Regenerate session IDs immediately after user authentication to prevent fixation.
• Use secure, random, and unpredictable session identifiers.
• Implement proper session expiration and invalidation mechanisms.
• Employ secure cookie attributes such as HttpOnly, Secure, and SameSite.
• Validate and restrict session ID acceptance only from legitimate sources.

Related Security Solutions

Web Application Firewalls (WAFs) can help detect and block suspicious session-related activities. Secure coding practices and session management libraries/frameworks provide built-in protections against session fixation. Security testing tools and vulnerability scanners can identify session fixation weaknesses during application assessments.