CWE - CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG) (4.19.1)
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    CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)

    Weakness ID: 337
    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) is initialized from a predictable seed, such as the process ID or system time.
    + Extended Description
    The use of predictable seeds significantly reduces the number of possible seeds that an attacker would need to test in order to predict which random numbers will be generated by the PRNG.
    + 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
    Use non-predictable inputs for seed generation.

    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.

    Implementation
    Use a PRNG that periodically re-seeds itself using input from high-quality sources, such as hardware devices with high entropy. However, do not re-seed too frequently, or else the entropy source might block.
    + 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)
    + 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


    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).



    + 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
    Cloud application on Kubernetes generates passwords using a weak random number generator based on deployment time.
    server uses erlang:now() to seed the PRNG, which results in a small search space for potential random seeds
    The removal of a couple lines of code caused Debian's OpenSSL Package to only use the current process ID for seeding a PRNG
    Router's PIN generation is based on rand(time(0)) seeding.
    cloud provider product uses a non-cryptographically secure PRNG and seeds it with the current time
    + 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
    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. 1152 SEI CERT Oracle Secure Coding Standard for Java - Guidelines 49. Miscellaneous (MSC)
    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. 1366 ICS Communications: Frail Security in Protocols
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1414 Comprehensive Categorization: Randomness
    MemberOf CategoryCategory - 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 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
    PLOVER Predictable Seed in PRNG
    The CERT Oracle Secure Coding Standard for Java (2011) MSC02-J Generate strong random numbers
    + 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. 2001-05-25.
    <https://csrc.nist.gov/files/pubs/fips/140-2/upd2/final/docs/fips1402.pdf>. (URL validated: 2025-05-21)
    [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>.
    [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
    2006-07-19
    (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
    2025-09-09
    (CWE 4.18, 2025-09-09)     		CWE Content Team MITRE
    updated References
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes, Relationships
    2023-04-27 CWE Content Team MITRE
    updated References, Relationships, Time_of_Introduction
    2022-10-13 CWE Content Team MITRE
    updated Observed_Examples
    2021-10-28 CWE Content Team MITRE
    updated Relationships
    2021-07-20 CWE Content Team MITRE
    updated Maintenance_Notes, Observed_Examples, Potential_Mitigations, References
    2020-02-24 CWE Content Team MITRE
    updated Description, Relationships
    2019-06-20 CWE Content Team MITRE
    updated Type
    2019-01-03 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2017-11-08 CWE Content Team MITRE
    updated Applicable_Platforms, Demonstrative_Examples, Description, Modes_of_Introduction, Name, References, Relationships
    2012-10-30 CWE Content Team MITRE
    updated Demonstrative_Examples, Potential_Mitigations
    2012-05-11 CWE Content Team MITRE
    updated References, Relationships
    2011-09-13 CWE Content Team MITRE
    updated Potential_Mitigations, References
    2011-06-27 CWE Content Team MITRE
    updated Common_Consequences
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences, Relationships, Taxonomy_Mappings
    2010-06-21 CWE Content Team MITRE
    updated Potential_Mitigations
    2009-12-28 CWE Content Team MITRE
    updated Potential_Mitigations
    2009-03-10 CWE Content Team MITRE
    updated Potential_Mitigations
    2008-09-08 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2008-07-01 Eric Dalci Cigital
    updated Time_of_Introduction
    2008-07-01 Sean Eidemiller Cigital
    added/updated demonstrative examples
    + Previous Entry Names
    Change Date Previous Entry Name
    2017-11-08 Predictable Seed in PRNG
    Page Last Updated: January 21, 2026