COMMON WEAKNESS ENUMERATIONDraft

CWE-342

Predictable Exact Value from Previous Values

An exact value or random number can be precisely predicted by observing previous values.

Abstraction

Base

Structure

Simple

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

An exact value or random number can be precisely predicted by observing previous values.

Root cause

How and when does the problem arise?

Lifecycle phase

Architecture and Design

Lifecycle phase

Implementation

Risk

What does successful exploitation lead to?

Varies by Context

Affected security scopes: Other

Defence

How is it prevented and fixed?

All phases

General mitigation and defence approach

Detail
Increase the entropy used to seed a PRNG.

Architecture and Design · Requirements

Libraries or Frameworks

Detail
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").

Implementation

Implementation-phase defence

Detail
Use a PRNG that periodically re-seeds itself using input from high-quality sources, such as hardware devices with high entropy. However, do not re-seed too frequently, or else the entropy source might block.