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CWE-6: J2EE Misconfiguration: Insufficient Session-ID Length

J2EE Misconfiguration: Insufficient Session-ID Length
Weakness ID: 6 (Weakness Variant)Status: Incomplete
+ Description

Description Summary

The J2EE application is configured to use an insufficient session ID length.

Extended Description

If an attacker can guess or steal a session ID, then he/she may be able to take over the user's session (called session hijacking). The number of possible session IDs increases with increased session ID length, making it more difficult to guess or steal a session ID.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms



+ Common Consequences

Technical Impact: Gain privileges / assume identity

If an attacker can guess an authenticated user's session identifier, they can take over the user's session.

+ Enabling Factors for Exploitation

If attackers use a botnet with hundreds or thousands of drone computers, it is reasonable to assume that they could attempt tens of thousands of guesses per second. If the web site in question is large and popular, a high volume of guessing might go unnoticed for some time.

+ Demonstrative Examples

Example 1

The following XML example code is a deployment descriptor for a Java web application deployed on a Sun Java Application Server. This deployment descriptor includes a session configuration property for configuring the session ID length.

(Bad Code)
Example Language: XML 
<property name="idLengthBytes" value="8">
<description>The number of bytes in this web module's session ID.</description>

This deployment descriptor has set the session ID length for this Java web application to 8 bytes (or 64 bits). The session ID length for Java web applications should be set to 16 bytes (128 bits) to prevent attackers from guessing and/or stealing a session ID and taking over a user's session.

Note for most application servers including the Sun Java Application Server the session ID length is by default set to 128 bits and should not be changed. And for many application servers the session ID length cannot be changed from this default setting. Check your application server documentation for the session ID length default setting and configuration options to ensure that the session ID length is set to 128 bits.

+ Potential Mitigations

Phase: Implementation

Session identifiers should be at least 128 bits long to prevent brute-force session guessing. A shorter session identifier leaves the application open to brute-force session guessing attacks.

Phase: Implementation

A lower bound on the number of valid session identifiers that are available to be guessed is the number of users that are active on a site at any given moment. However, any users that abandon their sessions without logging out will increase this number. (This is one of many good reasons to have a short inactive session timeout.) With a 64 bit session identifier, assume 32 bits of entropy. For a large web site, assume that the attacker can try 1,000 guesses per second and that there are 10,000 valid session identifiers at any given moment. Given these assumptions, the expected time for an attacker to successfully guess a valid session identifier is less than 4 minutes. Now assume a 128 bit session identifier that provides 64 bits of entropy. With a very large web site, an attacker might try 10,000 guesses per second with 100,000 valid session identifiers available to be guessed. Given these assumptions, the expected time for an attacker to successfully guess a valid session identifier is greater than 292 years.

+ Background Details

Session ID's can be used to identify communicating parties in a web environment.

The expected number of seconds required to guess a valid session identifier is given by the equation: (2^B+1)/(2*A*S) Where: - B is the number of bits of entropy in the session identifier. - A is the number of guesses an attacker can try each second. - S is the number of valid session identifiers that are valid and available to be guessed at any given time. The number of bits of entropy in the session identifier is always less than the total number of bits in the session identifier. For example, if session identifiers were provided in ascending order, there would be close to zero bits of entropy in the session identifier no matter the identifier's length. Assuming that the session identifiers are being generated using a good source of random numbers, we will estimate the number of bits of entropy in a session identifier to be half the total number of bits in the session identifier. For realistic identifier lengths this is possible, though perhaps optimistic.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
Seven Pernicious Kingdoms (primary)700
ChildOfCategoryCategory4J2EE Environment Issues
Development Concepts (primary)699
ChildOfWeakness BaseWeakness Base334Small Space of Random Values
Research Concepts (primary)1000
ChildOfCategoryCategory895SFP Cluster: Information Leak
Software Fault Pattern (SFP) Clusters (primary)888
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
7 Pernicious KingdomsJ2EE Misconfiguration: Insufficient Session-ID Length
+ Content History
Submission DateSubmitterOrganizationSource
Externally Mined
Modification DateModifierOrganizationSource
updated Time_of_Introduction
updated Relationships, Other_Notes, Taxonomy_Mappings
updated Background_Details, Description
updated Description, Other_Notes, References
updated Background_Details, Common_Consequences, Enabling_Factors_for_Exploitation, Other_Notes, Potential_Mitigations
updated Demonstrative_Examples
updated Common_Consequences
updated Demonstrative_Examples, Relationships
updated Potential_Mitigations
Page Last Updated: June 23, 2014