CWE - CWE-335: Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG) (4.18)

Home > CWE List > CWE-335: Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG) (4.18)

CWE Glossary Definition

CWE-335: Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)

Weakness ID: 335

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: 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.

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Description

The product uses a Pseudo-Random Number Generator (PRNG) but does not correctly manage seeds.

Extended Description

PRNGs are deterministic and, while their output appears random, they cannot actually create entropy. They rely on cryptographically secure and unique seeds for entropy so proper seeding is critical to the secure operation of the PRNG.

Management of seeds could be broken down into two main areas:

(1) protecting seeds as cryptographic material (such as a cryptographic key);
(2) whenever possible, using a uniquely generated seed from a cryptographically secure source

PRNGs require a seed as input to generate a stream of numbers that are functionally indistinguishable from random numbers. While the output is, in many cases, sufficient for cryptographic uses, the output of any PRNG is directly determined by the seed provided as input. If the seed can be ascertained by a third party, the entire output of the PRNG can be made known to them. As such, the seed should be kept secret and should ideally not be able to be guessed. For example, the current time may be a poor seed. Knowing the approximate time the PRNG was seeded greatly reduces the possible key space.

Seeds do not necessarily need to be unique, but reusing seeds may open up attacks if the seed is discovered.

Common Consequences

Section HelpThis 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 If a PRNG is used incorrectly, such as using the same seed for each initialization or using a predictable seed, then an attacker may be able to easily guess the seed and thus the random numbers. This could lead to unauthorized access to a system if the seed is used for authentication and authorization.

Relationships

Section Help 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 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 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.	336	Same Seed in Pseudo-Random Number Generator (PRNG)
ParentOf	Variant 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.	337	Predictable Seed in Pseudo-Random Number Generator (PRNG)
ParentOf	Variant 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.	339	Small Seed Space in PRNG

Relevant to the view "Software Development" (View-699)

Nature	Type	ID	Name
MemberOf	Category Category - a CWE entry that contains a set of other entries that share a common characteristic.	310	Cryptographic Issues
MemberOf	Category Category - a CWE entry that contains a set of other entries that share a common characteristic.	1213	Random Number Issues

Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)

Nature	Type	ID	Name
ChildOf	Class 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 Category - a CWE entry that contains a set of other entries that share a common characteristic.	1013	Encrypt Data

Modes Of Introduction

Section HelpThe 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
Implementation	REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Applicable Platforms

Section HelpThis 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

The following code uses a statistical PRNG to generate account IDs.

(bad code)

Example Language: Java

private static final long SEED = 1234567890;
public int generateAccountID() {

Random random = new Random(SEED);
return random.nextInt();

}

Because the program uses the same seed value for every invocation of the PRNG, its values are predictable, making the system vulnerable to attack.

Example 2

Both of these examples use a statistical PRNG seeded with the current value of the system clock to generate a random number:

(bad code)

Example Language: Java

Random random = new Random(System.currentTimeMillis());
int accountID = random.nextInt();

(bad code)

Example Language: C

srand(time());
int randNum = rand();

An attacker can easily predict the seed used by these PRNGs, and so also predict the stream of random numbers generated. Note these examples also exhibit CWE-338 (Use of Cryptographically Weak PRNG).

Example 3

This code grabs some random bytes and uses them for a seed in a PRNG, in order to generate a new cryptographic key.

(bad code)

Example Language: Python

# getting 2 bytes of randomness for the seeding the PRNG
seed = os.urandom(2)
random.seed(a=seed)
key = random.getrandbits(128)

Since only 2 bytes are used as a seed, an attacker will only need to guess 2^16 (65,536) values before being able to replicate the state of the 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
CVE-2020-7010	Cloud application on Kubernetes generates passwords using a weak random number generator based on deployment time.
CVE-2019-11495	server uses erlang:now() to seed the PRNG, which results in a small search space for potential random seeds
CVE-2018-12520	Product's PRNG is not seeded for the generation of session IDs
CVE-2016-10180	Router's PIN generation is based on rand(time(0)) seeding.

Memberships

Section HelpThis 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	ViewView - 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	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	905	SFP Primary Cluster: Predictability
MemberOf	CategoryCategory - 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	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1414	Comprehensive Categorization: Randomness

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	PRNG Seed Error

References

[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 20: Weak Random Numbers." Page 299. McGraw-Hill. 2010.

Content History

Submissions
Submission Date	Submitter	Organization
2006年07月19日 (CWE Draft 3, 2006年07月19日)	PLOVER
2006年07月19日 (CWE Draft 3, 2006年07月19日)
Modifications
Modification Date	Modifier	Organization
2023年10月26日	CWE Content Team	MITRE
2023年10月26日	updated Demonstrative_Examples
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated Relationships, Time_of_Introduction
2023年01月31日	CWE Content Team	MITRE
2023年01月31日	updated Description
2022年10月13日	CWE Content Team	MITRE
2022年10月13日	updated Observed_Examples
2021年10月28日	CWE Content Team	MITRE
2021年10月28日	updated Relationships
2021年07月20日	CWE Content Team	MITRE
2021年07月20日	updated Description, Maintenance_Notes, Observed_Examples
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships
2019年06月20日	CWE Content Team	MITRE
2019年06月20日	updated Relationships
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Applicable_Platforms, Description, Modes_of_Introduction, Name, Relationships, Type
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Common_Consequences, References, Relationships
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Relationships, Taxonomy_Mappings
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Time_of_Introduction
Previous Entry Names
Change Date	Previous Entry Name
2017年11月08日	PRNG Seed Error

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Page Last Updated: September 09, 2025

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