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Weakness · Medium

CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)

What it is

A Pseudo-Random Number Generator (PRNG) is initialized from a predictable seed, such as the process ID or system time.

MITRE CWE 4.19.1

Severity (our rating)
Medium
Likelihood of exploit
Not rated by MITRE
Introduced during
Implementation
Exploited in the wild
No CVE in CISA's catalog

In more detail

The use of predictable seeds significantly reduces the number of possible seeds that an attacker would need to test in order to predict which random numbers will be generated by the PRNG.

What an attacker can do

  • Varies by Context (Other)

How to prevent it

General

  • Use non-predictable inputs for seed generation.

Architecture and Design

  • Use products or modules that conform to FIPS 140-2 to avoid obvious entropy problems, or use the more recent FIPS 140-3 if possible.

Implementation

  • 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.

How to find it

  • Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

CWE-337 on MITRE's CWE site

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Source: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.