Weakness ID: 331
Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilitiesAbstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
Description
The product uses an algorithm or scheme that produces insufficient entropy, leaving patterns or clusters of values that are more likely to occur than others.
Common Consequences
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
| Impact | Details |
|---|---|
|
Bypass Protection Mechanism; Other |
Scope: Access Control, Other
An attacker could guess the random numbers generated and could gain unauthorized access to a system if the random numbers are used for authentication and authorization. |
Potential Mitigations
| Phase(s) | Mitigation |
|---|---|
|
Implementation |
Determine the necessary entropy to adequately provide for randomness and predictability. This can be achieved by increasing the number of bits of objects such as keys and seeds. |
Relationships
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Research Concepts" (View-1000)
| Nature | Type | ID | Name |
|---|---|---|---|
| ChildOf |
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
|
330 | Use of Insufficiently Random Values |
| ParentOf |
Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.
|
332 | Insufficient Entropy in PRNG |
| ParentOf |
Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.
|
333 | Improper Handling of Insufficient Entropy in TRNG |
Relevant to the view "Software Development" (View-699)
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)
| Nature | Type | ID | Name |
|---|---|---|---|
| ChildOf |
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
|
330 | Use of Insufficiently Random Values |
Relevant to the view "Architectural Concepts" (View-1008)
| Nature | Type | ID | Name |
|---|---|---|---|
| MemberOf |
Category - a CWE entry that contains a set of other entries that share a common characteristic.
|
1013 | Encrypt Data |
Modes
Of Introduction
The different Modes of Introduction provide information
about how and when this
weakness may be introduced. The Phase identifies a point in the life cycle at which
introduction
may occur, while the Note provides a typical scenario related to introduction during the
given
phase.
| Phase | Note |
|---|---|
| Architecture and Design | |
| Implementation | REALIZATION: This weakness is caused during implementation of an architectural security tactic. |
Applicable Platforms
This listing shows possible areas for which the given
weakness could appear. These
may be for specific named Languages, Operating Systems, Architectures, Paradigms,
Technologies,
or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
| Languages |
Class: Not Language-Specific (Undetermined Prevalence) |
Demonstrative Examples
Example 1
This code generates a unique random identifier for a user's session.
(bad code)
Example Language: PHP
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).
Example 2
The following code uses a statistical PRNG to create a URL for a receipt that remains active for some period of time after a purchase.
(bad code)
Example Language: Java
String GenerateReceiptURL(String baseUrl) {
Random ranGen = new Random();
ranGen.setSeed((new Date()).getTime());
return(baseUrl + ranGen.nextInt(400000000) + ".html");
}
This code uses the Random.nextInt() function to generate "unique" identifiers for the receipt pages it generates. Because Random.nextInt() is a statistical PRNG, it is easy for an attacker to guess the strings it generates. Although the underlying design of the receipt system is also faulty, it would be more secure if it used a random number generator that did not produce predictable receipt identifiers, such as a cryptographic PRNG.
Selected Observed
Examples
Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.
| Reference | Description |
|---|---|
|
Insufficiently random data used to generate session tokens using C rand(). Also, for certificate/key generation, uses a source that does not block when entropy is low. |
|
|
Chain: insufficient precision (CWE-1339) in random-number generator causes some zero bits to be reliably generated, reducing the amount of entropy (CWE-331) |
Weakness Ordinalities
| Ordinality | Description |
|---|---|
|
Primary |
(where the weakness exists independent of other weaknesses) |
Detection
Methods
| Method | Details |
|---|---|
|
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.) |
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
| Nature | Type | ID | Name |
|---|---|---|---|
| MemberOf |  View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). |
884 | CWE Cross-section |
| MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. |
905 | SFP Primary Cluster: Predictability |
| MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. |
1170 | SEI CERT C Coding Standard - Guidelines 48. Miscellaneous (MSC) |
| MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. |
1346 | OWASP Top Ten 2021 Category A02:2021 - Cryptographic Failures |
| MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. |
1414 | Comprehensive Categorization: Randomness |
| MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. |
1439 | OWASP Top Ten 2025 Category A04:2025 - Cryptographic Failures |
Vulnerability Mapping Notes
| Usage |
ALLOWED
(this CWE ID may be used to map to real-world vulnerabilities) |
| Reason | Acceptable-Use |
|
Rationale |
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities. |
|
Comments |
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction. |
Notes
Maintenance
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.
Taxonomy
Mappings
| Mapped Taxonomy Name | Node ID | Fit | Mapped Node Name |
|---|---|---|---|
| PLOVER | Insufficient Entropy | ||
| WASC | 11 | Brute Force | |
| CERT C Secure Coding | MSC32-C | Exact | Properly seed pseudorandom number generators |
References
| [REF-207] | John Viega and Gary McGraw. "Building Secure Software: How to Avoid Security Problems the Right Way". 1st Edition. Addison-Wesley. 2002. |
Content
History
| Submissions |
||
|---|---|---|
| Submission Date | Submitter | Organization |
|
2006-07-19
(CWE Draft 3, 2006-07-19) |
PLOVER | |
 Modifications |
||
| Modification Date | Modifier | Organization |
|
2025-12-11
(CWE 4.19, 2025-12-11) |
CWE Content Team | MITRE |
| updated Detection_Factors, Relationships, Weakness_Ordinalities | ||
|
2023-06-29
(CWE 4.12, 2023-06-29) |
CWE Content Team | MITRE |
| updated Mapping_Notes | ||
|
2023-04-27
(CWE 4.11, 2023-04-27) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2023-01-31
(CWE 4.10, 2023-01-31) |
CWE Content Team | MITRE |
| updated Description | ||
|
2021-10-28
(CWE 4.6, 2021-10-28) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2021-07-20
(CWE 4.5, 2021-07-20) |
CWE Content Team | MITRE |
| updated Maintenance_Notes, Observed_Examples | ||
|
2020-02-24
(CWE 4.0, 2020-02-24) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2019-06-20
(CWE 3.3, 2019-06-20) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2019-01-03
(CWE 3.2, 2019-01-03) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2017-11-08
(CWE 3.0, 2017-11-08) |
CWE Content Team | MITRE |
| updated Applicable_Platforms, Modes_of_Introduction, Relationships, Taxonomy_Mappings | ||
|
2015-12-07
(CWE 2.9, 2015-12-07) |
CWE Content Team | MITRE |
| updated Relationships | ||
|
2012-10-30
(CWE 2.3, 2012-10-30) |
CWE Content Team | MITRE |
| updated Potential_Mitigations | ||
|
2012-05-11
(CWE 2.2, 2012-05-15) |
CWE Content Team | MITRE |
| updated Common_Consequences, Demonstrative_Examples, References, Relationships | ||
|
2011-06-01
(CWE 1.13, 2011-06-01) |
CWE Content Team | MITRE |
| updated Common_Consequences | ||
|
2010-02-16
(CWE 1.8, 2010-02-16) |
CWE Content Team | MITRE |
| updated Taxonomy_Mappings | ||
|
2008-09-08
(CWE 1.0, 2008-09-09) |
CWE Content Team | MITRE |
| updated Relationships, Taxonomy_Mappings | ||
|
2008-07-01
(CWE 1.0, 2008-09-09) |
Eric Dalci | Cigital |
| updated Time_of_Introduction | ||