CWE

Common Weakness Enumeration

A Community-Developed List of Software & Hardware Weakness Types

CWE Top 25 Most Dangerous Weaknesses
Home > CWE List > CWE- Individual Dictionary Definition (4.5)  
ID

CWE-336: Same Seed in Pseudo-Random Number Generator (PRNG)

Weakness ID: 336
Abstraction: Variant
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
A Pseudo-Random Number Generator (PRNG) uses the same seed each time the product is initialized.
+ Extended Description
Given the deterministic nature of PRNGs, using the same seed for each initialization will lead to the same output in the same order. If an attacker can guess (or knows) the seed, then the attacker may be able to determine the random numbers that will be produced from the PRNG.
+ Relationships
Section HelpThis 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" (CWE-1000)
NatureTypeIDName
ChildOfBaseBase - 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.335Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)
Section HelpThis 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 "Architectural Concepts" (CWE-1008)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1013Encrypt 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.
PhaseNote
Architecture and DesignThe developer might not consider the need to use new seeds during design.
ImplementationREALIZATION: 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: Language-Independent (Undetermined Prevalence)

+ 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.
ScopeImpactLikelihood
Other
Access Control

Technical Impact: Other; Bypass Protection Mechanism

+ 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

This code attempts to generate 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.

If the user IDs are generated sequentially, or otherwise restricted to a narrow range of values, then this example also exhibits a Small Seed Space (CWE-339).

+ Potential Mitigations

Phase: Architecture and Design

Do not reuse PRNG seeds. Consider a PRNG that periodically re-seeds itself as needed from a high quality pseudo-random output, such as hardware devices.

Phases: 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.
+ 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.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.861The CERT Oracle Secure Coding Standard for Java (2011) Chapter 18 - Miscellaneous (MSC)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.905SFP Primary Cluster: Predictability
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1152SEI CERT Oracle Secure Coding Standard for Java - Guidelines 49. Miscellaneous (MSC)
+ 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 NameNode IDFitMapped Node Name
PLOVERSame Seed in PRNG
The CERT Oracle Secure Coding Standard for Java (2011)MSC02-JGenerate strong random numbers
+ References
[REF-267] Information Technology Laboratory, National Institute of Standards and Technology. "SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES". Annex C, Approved Random Number Generators. 2001-05-25. <http://csrc.nist.gov/publications/fips/fips140-2/fips1402.pdf>.
[REF-1192] Information Technology Laboratory, National Institute of Standards and Technology. "FIPS PUB 140-3: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES". 2019-03-22. <https://csrc.nist.gov/publications/detail/fips/140/3/final>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2006-07-19PLOVER
+ Modifications
Modification DateModifierOrganization
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-03-10CWE Content TeamMITRE
updated Potential_Mitigations
2009-12-28CWE Content TeamMITRE
updated Potential_Mitigations
2010-06-21CWE Content TeamMITRE
updated Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-09-13CWE Content TeamMITRE
updated Potential_Mitigations, References
2012-05-11CWE Content TeamMITRE
updated Relationships
2014-07-30CWE Content TeamMITRE
updated Demonstrative_Examples
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Description, Modes_of_Introduction, Name, References, Relationships
2019-01-03CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2019-06-20CWE Content TeamMITRE
updated Type
2020-02-24CWE Content TeamMITRE
updated Relationships
2021-07-20CWE Content TeamMITRE
updated Demonstrative_Examples, Description, Maintenance_Notes, Modes_of_Introduction, Potential_Mitigations, References
+ Previous Entry Names
Change DatePrevious Entry Name
2017-11-08Same Seed in PRNG
More information is available — Please select a different filter.
Page Last Updated: July 20, 2021