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CWE-384: Session Fixation

Weakness ID: 384
Abstraction: Compound
Structure: Composite
Status: Incomplete
Presentation Filter:
+ Description
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.
+ Extended Description

Such a scenario is commonly observed when:

1. A web application authenticates a user without first invalidating the existing session, thereby continuing to use the session already associated with the user.
2. An attacker is able to force a known session identifier on a user so that, once the user authenticates, the attacker has access to the authenticated session.
3. The application or container uses predictable session identifiers. In the generic exploit of session fixation vulnerabilities, an attacker creates a new session on a web application and records the associated session identifier. The attacker then causes the victim to associate, and possibly authenticate, against the server using that session identifier, giving the attacker access to the user's account through the active session.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
ChildOfClassClass287Improper Authentication
+ Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
ChildOfClassClass287Improper Authentication
+ Relevant to the view "Architectural Concepts" (CWE-1008)
MemberOfCategoryCategory1018Manage User Sessions
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory3617PK - Time and State
ChildOfClassClass287Improper Authentication
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Access Control

Technical Impact: Gain Privileges or Assume Identity

+ Demonstrative Examples

Example 1

The following example shows a snippet of code from a J2EE web application where the application authenticates users with LoginContext.login() without first calling HttpSession.invalidate().

(bad code)
Example Language: Java 
private void auth(LoginContext lc, HttpSession session) throws LoginException {


In order to exploit the code above, an attacker could first create a session (perhaps by logging into the application) from a public terminal, record the session identifier assigned by the application, and reset the browser to the login page. Next, a victim sits down at the same public terminal, notices the browser open to the login page of the site, and enters credentials to authenticate against the application. The code responsible for authenticating the victim continues to use the pre-existing session identifier, now the attacker simply uses the session identifier recorded earlier to access the victim's active session, providing nearly unrestricted access to the victim's account for the lifetime of the session. Even given a vulnerable application, the success of the specific attack described here is dependent on several factors working in the favor of the attacker: access to an unmonitored public terminal, the ability to keep the compromised session active and a victim interested in logging into the vulnerable application on the public terminal.

In most circumstances, the first two challenges are surmountable given a sufficient investment of time. Finding a victim who is both using a public terminal and interested in logging into the vulnerable application is possible as well, so long as the site is reasonably popular. The less well known the site is, the lower the odds of an interested victim using the public terminal and the lower the chance of success for the attack vector described above. The biggest challenge an attacker faces in exploiting session fixation vulnerabilities is inducing victims to authenticate against the vulnerable application using a session identifier known to the attacker.

In the example above, the attacker did this through a direct method that is not subtle and does not scale suitably for attacks involving less well-known web sites. However, do not be lulled into complacency; attackers have many tools in their belts that help bypass the limitations of this attack vector. The most common technique employed by attackers involves taking advantage of cross-site scripting or HTTP response splitting vulnerabilities in the target site [12]. By tricking the victim into submitting a malicious request to a vulnerable application that reflects JavaScript or other code back to the victim's browser, an attacker can create a cookie that will cause the victim to reuse a session identifier controlled by the attacker. It is worth noting that cookies are often tied to the top level domain associated with a given URL. If multiple applications reside on the same top level domain, such as and, a vulnerability in one application can allow an attacker to set a cookie with a fixed session identifier that will be used in all interactions with any application on the domain [29].

Example 2

The following example shows a snippet of code from a J2EE web application where the application authenticates users with a direct post to the <code>j_security_check</code>, which typically does not invalidate the existing session before processing the login request.

(bad code)
Example Language: HTML 
<form method="POST" action="j_security_check">
<input type="text" name="j_username">
<input type="text" name="j_password">

+ Potential Mitigations

Phase: Architecture and Design

Invalidate any existing session identifiers prior to authorizing a new user session.

Phase: Architecture and Design

For platforms such as ASP that do not generate new values for sessionid cookies, utilize a secondary cookie. In this approach, set a secondary cookie on the user's browser to a random value and set a session variable to the same value. If the session variable and the cookie value ever don't match, invalidate the session, and force the user to log on again.
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
+ Notes


Other attack vectors include DNS poisoning and related network based attacks where an attacker causes the user to visit a malicious site by redirecting a request for a valid site. Network based attacks typically involve a physical presence on the victim's network or control of a compromised machine on the network, which makes them harder to exploit remotely, but their significance should not be overlooked. Less secure session management mechanisms, such as the default implementation in Apache Tomcat, allow session identifiers normally expected in a cookie to be specified on the URL as well, which enables an attacker to cause a victim to use a fixed session identifier simply by emailing a malicious URL.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
7 Pernicious KingdomsSession Fixation
OWASP Top Ten 2004A3CWE More SpecificBroken Authentication and Session Management
WASC37Session Fixation
+ Content History
Submission DateSubmitterOrganization
7 Pernicious Kingdoms
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITRE
updated Description, Relationships, Other_Notes, Taxonomy_Mappings
2009-07-27CWE Content TeamMITRE
updated Demonstrative_Examples, Related_Attack_Patterns
2010-02-16CWE Content TeamMITRE
updated Taxonomy_Mappings
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2013-07-17CWE Content TeamMITRE
updated Relationships
2015-12-07CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Modes_of_Introduction, Relationships

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Page Last Updated: January 18, 2018