CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)Weakness ID: 337 Vulnerability Mapping:
ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction: VariantVariant - 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. |
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 This 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.Scope | Impact | Likelihood |
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Other
| Technical Impact: Varies by Context | |
Potential Mitigations
Use non-predictable inputs for seed generation. |
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. |
Phase: 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 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" (CWE-1000) Nature | Type | ID | Name |
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ChildOf | 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) |
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 "Architectural Concepts" (CWE-1008) Nature | Type | ID | Name |
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MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. | 1013 | Encrypt Data |
Modes Of Introduction The 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 |
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Implementation | REALIZATION: This weakness is caused during implementation of an architectural security tactic. |
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). Observed Examples 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 |
Memberships This 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. Vulnerability Mapping Notes Usage: ALLOWED (this CWE ID could 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
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[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.
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Content History Submissions |
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Submission Date | Submitter | Organization |
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2006-07-19 (CWE Draft 3, 2006-07-19) | PLOVER | | | Modifications |
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Modification Date | Modifier | Organization |
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2008-07-01 | Sean Eidemiller | Cigital | added/updated demonstrative examples | 2008-07-01 | Eric Dalci | Cigital | updated Time_of_Introduction | 2008-09-08 | CWE Content Team | MITRE | updated Relationships, Taxonomy_Mappings | 2009-03-10 | CWE Content Team | MITRE | updated Potential_Mitigations | 2009-12-28 | CWE Content Team | MITRE | updated Potential_Mitigations | 2010-06-21 | CWE Content Team | MITRE | updated Potential_Mitigations | 2011-06-01 | CWE Content Team | MITRE | updated Common_Consequences, Relationships, Taxonomy_Mappings | 2011-06-27 | CWE Content Team | MITRE | updated Common_Consequences | 2011-09-13 | CWE Content Team | MITRE | updated Potential_Mitigations, References | 2012-05-11 | CWE Content Team | MITRE | updated References, Relationships | 2012-10-30 | CWE Content Team | MITRE | updated Demonstrative_Examples, Potential_Mitigations | 2017-11-08 | CWE Content Team | MITRE | updated Applicable_Platforms, Demonstrative_Examples, Description, Modes_of_Introduction, Name, References, Relationships | 2019-01-03 | CWE Content Team | MITRE | updated Relationships, Taxonomy_Mappings | 2019-06-20 | CWE Content Team | MITRE | updated Type | 2020-02-24 | CWE Content Team | MITRE | updated Description, Relationships | 2021-07-20 | CWE Content Team | MITRE | updated Maintenance_Notes, Observed_Examples, Potential_Mitigations, References | 2021-10-28 | CWE Content Team | MITRE | updated Relationships | 2022-10-13 | CWE Content Team | MITRE | updated Observed_Examples | 2023-04-27 | CWE Content Team | MITRE | updated References, Relationships, Time_of_Introduction | 2023-06-29 | CWE Content Team | MITRE | updated Mapping_Notes, Relationships | Previous Entry Names |
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Change Date | Previous Entry Name |
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2017-11-08 | Predictable Seed in PRNG | |
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