CWE - CWE-339: Small Seed Space in PRNG (4.18)

Home > CWE List > CWE-339: Small Seed Space in PRNG (4.18)

CWE Glossary Definition

CWE-339: Small Seed Space in PRNG

Weakness ID: 339

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

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Description

A Pseudo-Random Number Generator (PRNG) uses a relatively small seed space, which makes it more susceptible to brute force attacks.

Extended Description

PRNGs are entirely deterministic once seeded, so it should be extremely difficult to guess the seed. If an attacker can collect the outputs of a PRNG and then brute force the seed by trying every possibility to see which seed matches the observed output, then the attacker will know the output of any subsequent calls to the PRNG. A small seed space implies that the attacker will have far fewer possible values to try to exhaust all possibilities.

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
Varies by Context	Scope: Other

Potential Mitigations

Phase(s)	Mitigation
Architecture and Design	Use well vetted pseudo-random number generating algorithms with adequate length seeds. Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a "random enough" number.
Architecture and Design; Requirements	Strategy: Libraries or Frameworks Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.

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	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.	335	Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)
PeerOf	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.	341	Predictable from Observable State

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

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-2019-10908	product generates passwords via org.apache.commons.lang.RandomStringUtils, which uses java.util.Random internally. This PRNG has only a 48-bit seed.

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	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.	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 Variant 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

This entry may have a chaining relationship with predictable from observable state (CWE-341).

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	Small Seed Space in PRNG

References

[REF-267] Information Technology Laboratory, National Institute of Standards and Technology. "FIPS PUB 140-2: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES". Annex C, Approved Random Number Generators. 2001年05月25日.
<https://csrc.nist.gov/files/pubs/fips/140-2/upd2/final/docs/fips1402.pdf>. (URL validated: 2025年05月21日)

[REF-1192] Information Technology Laboratory, National Institute of Standards and Technology. "FIPS PUB 140-3: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES". 2019年03月22日.
<https://csrc.nist.gov/publications/detail/fips/140/3/final>.

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
2025年09月09日 (CWE 4.18, 2025年09月09日)	CWE Content Team	MITRE
2025年09月09日 (CWE 4.18, 2025年09月09日)	updated References
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 References, Relationships, Time_of_Introduction
2021年07月20日	CWE Content Team	MITRE
2021年07月20日	updated Demonstrative_Examples, Description, Maintenance_Notes, Observed_Examples, Potential_Mitigations, References
2021年03月15日	CWE Content Team	MITRE
2021年03月15日	updated Maintenance_Notes
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 Type
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Applicable_Platforms, Modes_of_Introduction, References, Relationships
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Potential_Mitigations
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Relationships
2011年09月13日	CWE Content Team	MITRE
2011年09月13日	updated Potential_Mitigations, References
2011年06月27日	CWE Content Team	MITRE
2011年06月27日	updated Common_Consequences
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2010年06月21日	CWE Content Team	MITRE
2010年06月21日	updated Observed_Examples, Potential_Mitigations
2009年12月28日	CWE Content Team	MITRE
2009年12月28日	updated Potential_Mitigations
2009年03月10日	CWE Content Team	MITRE
2009年03月10日	updated Potential_Mitigations
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Maintenance_Notes, Relationships, Taxonomy_Mappings
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Time_of_Introduction

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Page Last Updated: September 09, 2025

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