The product uses a scheme that generates numbers or identifiers that are more predictable than required.

Primary

Architecture and Design

Implementation

Other
Varies by Context

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.)

This code generates a unique random identifier for a user's session.

function generateSessionID($userID){srand($userID);return rand();}

Because the seed for the PRNG is always the user's ID, the session ID will always be the same. An attacker could thus predict any user's session ID and potentially hijack the session.
This example also exhibits a Small Seed Space (CWE-339).

CVE-2022-29330
Product for administering PBX systems uses predictable identifiers and timestamps for filenames (CWE-340) which allows attackers to access files via direct request (CWE-425).
https://www.cve.org/CVERecord?id=CVE-2022-29330

CVE-2001-1141
PRNG allows attackers to use the output of small PRNG requests to determine the internal state information, which could be used by attackers to predict future pseudo-random numbers.
https://www.cve.org/CVERecord?id=CVE-2001-1141

CVE-1999-0074
Listening TCP ports are sequentially allocated, allowing spoofing attacks.
https://www.cve.org/CVERecord?id=CVE-1999-0074

Predictability problems

11
Brute Force

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

As 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.

PLOVER
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2010-02-16
updated Taxonomy_Mappings

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated References, Relationships

CWE Content Team
MITRE
2020-02-24
updated Description, Name, Relationships

CWE Content Team
MITRE
2021-07-20
updated Maintenance_Notes

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Observed_Examples

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Demonstrative_Examples

CWE Content Team
MITRE
2024-07-16
4.15
2024-07-16
updated Relationships

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Detection_Factors, Relationships, Weakness_Ordinalities

Predictability Problems