CWE-343: Predictable Value Range from Previous Values

Extended Description

The output of a random number generator should not be predictable based on observations of previous values. In some cases, an attacker cannot predict the exact value that will be produced next, but can narrow down the possibilities significantly. This reduces the amount of effort to perform a brute force attack. For example, suppose the product generates random numbers between 1 and 100, but it always produces a larger value until it reaches 100. If the generator produces an 80, then the attacker knows that the next value will be somewhere between 81 and 100. Instead of 100 possibilities, the attacker only needs to consider 20.

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-343 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-343, Predictable Value Range from Previous Values, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Apply Libraries or Frameworks controls for Predictable Value Range from Previous Values

MITRE associates mitigation with Architecture and Design, Requirements, and Implementation; the listed strategies include Libraries or Frameworks; recorded impacts include Varies by Context. Use these source-defined anchors to turn CWE-343 into implementation, review, and verification checks for the affected component.

CWE-343: Predictable Value Range from Previous Values — MITRE CWE

Triage CWE-343 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-343, Predictable Value Range from Previous Values, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-343

Apply MITRE's full root-cause mapping guidance when using CWE-343, Predictable Value Range from Previous Values. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-343 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-343, Predictable Value Range from Previous Values. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-343: Predictable Value Range from Previous Values?+

CWE-343: Predictable Value Range from Previous Values is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product's random number generator produces a series of values which, when observed, can be used to infer a relatively small range of possibilities for the next value that could be generated. The output of a random number generator should not be predictable based on observations of previous values. In some cases, an attacker cannot predict the exact value that will be produced next, but can narrow down the possibilities significantly. This reduces the amount of effort to perform a brute force attack. For example, suppose the product generates random numbers between 1 and 100, but it always produces a larger value until it reaches 100. If the generator produces an 80, then the attacker knows that the next value will be somewhere between 81 and 100. Instead of 100 possibilities, the attacker only needs to consider 20.

What are the security consequences of Predictable Value Range from Previous Values?+

If exploited, CWE-343 (Predictable Value Range from Previous Values) it can compromise Other, leading to outcomes such as Varies by Context.

How do you prevent or mitigate Predictable Value Range from Previous Values?+

Recommended mitigations for CWE-343 include: Increase the entropy used to seed a PRNG.

Which programming languages are affected by Predictable Value Range from Previous Values?+

CWE-343 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-343 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-343: Predictable Value Range from Previous Values

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