Session Fixation
Incomplete Compound
Structure: Composite
Description
Session fixation occurs when an application authenticates a user without first destroying the previous session ID. This allows an attacker who knows that session identifier to hijack the user's authenticated session.
This vulnerability typically happens in three scenarios: when an app authenticates a user while keeping their old session active, when an attacker can force a user to use a known session identifier, or when the application uses predictable session IDs that are easy to guess. Essentially, the system fails to issue a fresh, secure session token upon login, leaving the door open for session theft. In a common attack, the attacker first creates a session on the target application and notes its identifier. They then trick or redirect the victim into using that same session ID, often before the victim logs in. Once the victim authenticates, the attacker can use the known identifier to access the now-privileged session, effectively taking over the user's account without needing their credentials.
Common Consequences 1
Scope: Access Control
Impact: Gain Privileges or Assume Identity
Potential Mitigations 3
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.
Phase: Operation
Strategy: Firewall
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Effectiveness: Moderate
Demonstrative Examples 2
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().
Code Example:
Bad
Java
javaIn 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 bank.example.com and recipes.example.com, 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 example.com [29].
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.
Code Example:
Bad
HTML
htmlObserved Examples 1
CVE-2022-2820Website software for game servers does not proprerly terminate user sessions, allowing for possible session fixation
References 2
Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors
Katrina Tsipenyuk, Brian Chess, and Gary McGraw
NIST Workshop on Software Security Assurance Tools Techniques and Metrics • NIST
07-11-2005
ID: REF-6
D3FEND: Application Layer Firewall
D3FEND
ID: REF-1481
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Architecture and Design
Implementation
Related Attack Patterns
- 21DEPRECATED: Pathname Traversal and Equivalence Errors
- 31Path Traversal: 'dir\..\..\filename'
- 39Path Traversal: 'C:dirname'
- 59Improper Link Resolution Before File Access ('Link Following')
- 60DEPRECATED: UNIX Path Link Problems
- 61UNIX Symbolic Link (Symlink) Following
- 196Unsigned to Signed Conversion Error
Related Weaknesses
Requires:
Origin Validation Error (CWE-346)
Taxonomy Mapping
- 7 Pernicious Kingdoms
- OWASP Top Ten 2004
- WASC
Notes
OtherOther 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.