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Base weakness

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CWE-342: Predictable Exact Value from Previous Values

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

Last updated May 1, 2026

6

Recorded CVEs

With this primary weakness

0

KEVs

In the CISA KEV catalog

Not rated

Likelihood of exploit

Per MITRE

Base

Abstraction

MITRE classification

Overview

CWE-342 (Predictable Exact Value from Previous Values) is a base-level software weakness catalogued by MITRE in the Common Weakness Enumeration (CWE). It describes a recurring type of mistake that can lead to exploitable security vulnerabilities.

Real-world CVEs

6 recorded CVEs are caused by CWE-342 (Predictable Exact Value from Previous Values). The highest-severity and most recent are shown first.

Unscored · EPSS 67th

2022-04-11

CVE-2020-16226

Mitsubishi Electric Multiple Products

Unscored · EPSS 65th

2020-10-05

CVE-2014-9196

Eaton’s Cooper Power Series Form 6 Control and Idea/IdeaPlus Relays with Ethernet

Unscored · EPSS 86th

2015-07-20

Common consequences

What can happen when CWE-342 is exploited.

Varies by Context

Affects: Other

How it happens

When it is introduced

Typically introduced during these phases of the software lifecycle.

Architecture and Design

Implementation

How to prevent it

Practical mitigations for CWE-342, grouped by where in the lifecycle they apply.

Increase the entropy used to seed a PRNG.

Architecture and Design

Requirements

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").

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.

Illustrative examples

Real CVEs that MITRE cites as examples of this weakness.

CVE-2002-1463 — Firewall generates easily predictable initial sequence numbers (ISN), which allows remote attackers to spoof connections.
CVE-1999-0074 — Listening TCP ports are sequentially allocated, allowing spoofing attacks.
CVE-1999-0077 — Predictable TCP sequence numbers allow spoofing.
CVE-2000-0335 — DNS resolver uses predictable IDs, allowing a local user to spoof DNS query results.

Terminology & mappings

Mapped taxonomies

PLOVER: Predictable Exact Value from Previous Values

Frequently asked questions

Common questions about CWE-342.

What is CWE-342?

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

What CVEs are caused by CWE-342?

6 recorded CVEs are attributed to CWE-342, including CVE-2022-29930, CVE-2020-28388, CVE-2023-3373.

How do you prevent CWE-342?

Increase the entropy used to seed a PRNG.

What are the consequences of CWE-342?

Exploiting CWE-342 can lead to: Varies by Context.

Is CWE-342 actively exploited?

6 recorded CVEs are caused by CWE-342; none are currently in CISA's KEV catalog of actively exploited flaws.

References

Weakness data is sourced from the MITRE CWE catalog (v4.20). CVE associations are aggregated and kept current by RadicalNotion.AI.

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