CWE - CWE-333: Improper Handling of Insufficient Entropy in TRNG (4.19.1)
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    CWE-333: Improper Handling of Insufficient Entropy in TRNG

    Weakness ID: 333
    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
    True random number generators (TRNG) generally have a limited source of entropy and therefore can fail or block.
    + Extended Description
    The rate at which true random numbers can be generated is limited. It is important that one uses them only when they are needed for security.
    + 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

    DoS: Crash, Exit, or Restart

    		Scope: Availability

    A program may crash or block if it runs out of random numbers.
    + Potential Mitigations
    Phase(s) Mitigation

    Implementation
    Rather than failing on a lack of random numbers, it is often preferable to wait for more numbers to be created.
    + 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. 331 Insufficient Entropy
    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. 755 Improper Handling of Exceptional Conditions
    + 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
    Architecture and Design
    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)

    + Likelihood Of Exploit
    Low
    + Demonstrative Examples

    Example 1


    This code uses a TRNG to generate a unique session id for new connections to a server:

    (bad code)
    Example Language: C 
    while (1){
    if (haveNewConnection()){
    if (hwRandom()){
    int sessionID = hwRandom();
    createNewConnection(sessionID);
    } } }

    This code does not attempt to limit the number of new connections or make sure the TRNG can successfully generate a new random number. An attacker may be able to create many new connections and exhaust the entropy of the TRNG. The TRNG may then block and cause the program to crash or hang.



    + Weakness Ordinalities
    Ordinality Description
    Primary
    (where the weakness exists independent of other weaknesses)
    Resultant
    (where the weakness is typically related to the presence of some other weaknesses)
    + 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. 861 The CERT Oracle Secure Coding Standard for Java (2011) Chapter 18 - Miscellaneous (MSC)
    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

    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
    CLASP Failure of TRNG
    The CERT Oracle Secure Coding Standard for Java (2011) MSC02-J Generate strong random numbers
    + References
    [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005.
    <https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024-11-17)
    + Content History
    + Submissions
    Submission Date Submitter Organization
    2006-07-19
    (CWE Draft 3, 2006-07-19)     		CLASP
    + Modifications
    Modification Date Modifier Organization
    2025-12-11
    (CWE 4.19, 2025-12-11)     		CWE Content Team MITRE
    updated Weakness_Ordinalities
    2024-02-29
    (CWE 4.14, 2024-02-29)     		CWE Content Team MITRE
    updated Relationships
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes
    2023-04-27 CWE Content Team MITRE
    updated Relationships
    2021-07-20 CWE Content Team MITRE
    updated Maintenance_Notes
    2020-02-24 CWE Content Team MITRE
    updated References, Relationships
    2019-01-03 CWE Content Team MITRE
    updated Taxonomy_Mappings
    2017-11-08 CWE Content Team MITRE
    updated Applicable_Platforms, Likelihood_of_Exploit, Modes_of_Introduction, Relationships
    2012-10-30 CWE Content Team MITRE
    updated Demonstrative_Examples
    2012-05-11 CWE Content Team MITRE
    updated Relationships
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences, Relationships, Taxonomy_Mappings
    2009-10-29 CWE Content Team MITRE
    updated Description, Other_Notes
    2009-05-27 CWE Content Team MITRE
    updated Description, Name
    2008-09-08 CWE Content Team MITRE
    updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
    2008-07-01 Eric Dalci Cigital
    updated Time_of_Introduction
    + Previous Entry Names
    Change Date Previous Entry Name
    2008-04-11 Failure of TRNG
    2009-05-27 Failure to Handle Insufficient Entropy in TRNG
    Page Last Updated: January 21, 2026