Small Space of Random Values

Draft Base

Structure: Simple

Description

The number of possible random values is smaller than needed by the product, making it more susceptible to brute force attacks.

Common Consequences 1

Scope: Access ControlOther

Impact: Bypass Protection MechanismOther

An attacker could easily guess the values used. This could lead to unauthorized access to a system if the seed is used for authentication and authorization.

Potential Mitigations 1

Phase: Architecture and DesignRequirements

Strategy: Libraries or Frameworks

Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").

Demonstrative Examples 1

ID : DX-47

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.

Code Example:Bad
XML
xml

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.

Observed Examples 4

CVE-2002-0583Product uses 5 alphanumeric characters for filenames of expense claim reports, stored under web root.

CVE-2002-0903Product uses small number of random numbers for a code to approve an action, and also uses predictable new user IDs, allowing attackers to hijack new accounts.

CVE-2003-1230SYN cookies implementation only uses 32-bit keys, making it easier to brute force ISN.

CVE-2004-0230Complex predictability / randomness (reduced space).

References 2

FIPS PUB 140-2: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES

Information Technology Laboratory, National Institute of Standards and Technology

25-05-2001

https://csrc.nist.gov/files/pubs/fips/140-2/upd2/final/docs/fips1402.pdf(2025-05-21)

ID: REF-267

24 Deadly Sins of Software Security

Michael Howard, David LeBlanc, and John Viega

McGraw-Hill

2010

ID: REF-44

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Architecture and Design

Implementation

Related Weaknesses

ChildOf:

Use of Insufficiently Random Values (CWE-330)

Taxonomy Mapping

PLOVER

Notes

MaintenanceAs of CWE 4.5, terminology related to randomness, entropy, and predictability can vary widely. Within the developer and other communities, "randomness" is used heavily. However, within cryptography, "entropy" is distinct, typically implied as a measurement. There are no commonly-used definitions, even within standards documents and cryptography papers. Future versions of CWE will attempt to define these terms and, if necessary, distinguish between them in ways that are appropriate for different communities but do not reduce the usability of CWE for mapping, understanding, or other scenarios.