CAPEC Details
Name Session Fixation
Likelyhood of attack Typical severity
Medium High
Summary The attacker induces a client to establish a session with the target software using a session identifier provided by the attacker. Once the user successfully authenticates to the target software, the attacker uses the (now privileged) session identifier in their own transactions. This attack leverages the fact that the target software either relies on client-generated session identifiers or maintains the same session identifiers after privilege elevation.
Prerequisites Session identifiers that remain unchanged when the privilege levels change. Permissive session management mechanism that accepts random user-generated session identifiers Predictable session identifiers
Execution Flow
Step Phase Description Techniques
1 Explore [Setup the Attack] Setup a session: The attacker has to setup a trap session that provides a valid session identifier, or select an arbitrary identifier, depending on the mechanism employed by the application. A trap session is a dummy session established with the application by the attacker and is used solely for the purpose of obtaining valid session identifiers. The attacker may also be required to periodically refresh the trap session in order to obtain valid session identifiers.
  • The attacker chooses a predefined identifier that they know.
  • The attacker creates a trap session for the victim.
2 Experiment [Attract a Victim] Fixate the session: The attacker now needs to transfer the session identifier from the trap session to the victim by introducing the session identifier into the victim's browser. This is known as fixating the session. The session identifier can be introduced into the victim's browser by leveraging cross site scripting vulnerability, using META tags or setting HTTP response headers in a variety of ways.
  • Attackers can put links on web sites (such as forums, blogs, or comment forms).
  • Attackers can establish rogue proxy servers for network protocols that give out the session ID and then redirect the connection to the legitimate service.
  • Attackers can email attack URLs to potential victims through spam and phishing techniques.
3 Exploit [Abuse the Victim's Session] Takeover the fixated session: Once the victim has achieved a higher level of privilege, possibly by logging into the application, the attacker can now take over the session using the fixated session identifier.
  • The attacker loads the predefined session ID into their browser and browses to protected data or functionality.
  • The attacker loads the predefined session ID into their software and utilizes functionality with the rights of the victim.
Solutions Use a strict session management mechanism that only accepts locally generated session identifiers: This prevents attackers from fixating session identifiers of their own choice. Regenerate and destroy session identifiers when there is a change in the level of privilege: This ensures that even though a potential victim may have followed a link with a fixated identifier, a new one is issued when the level of privilege changes. Use session identifiers that are difficult to guess or brute-force: One way for the attackers to obtain valid session identifiers is by brute-forcing or guessing them. By choosing session identifiers that are sufficiently random, brute-forcing or guessing becomes very difficult.
Related Weaknesses
CWE ID Description
CWE-361 7PK - Time and State
CWE-384 Session Fixation
CWE-664 Improper Control of a Resource Through its Lifetime
CWE-732 Incorrect Permission Assignment for Critical Resource
Related CAPECS
CAPEC ID Description
CAPEC-593 This type of attack involves an adversary that exploits weaknesses in an application's use of sessions in performing authentication. The adversary is able to steal or manipulate an active session and use it to gain unathorized access to the application.
Taxonomy: WASC
Entry ID Entry Name
37 Session Fixation
Taxonomy: OWASP Attacks
Entry ID Entry Name
Link Session fixation