CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)Weakness ID: 338 Vulnerability Mapping:
ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction: BaseBase - 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. |
Description The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong. Extended Description When a non-cryptographic PRNG is used in a cryptographic context, it can expose the cryptography to certain types of attacks. Often a pseudo-random number generator (PRNG) is not designed for cryptography. Sometimes a mediocre source of randomness is sufficient or preferable for algorithms that use random numbers. Weak generators generally take less processing power and/or do not use the precious, finite, entropy sources on a system. While such PRNGs might have very useful features, these same features could be used to break the cryptography. 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 |
---|
Access Control
| Technical Impact: Bypass Protection Mechanism If a PRNG is used for authentication and authorization, such as a session ID or a seed for generating a cryptographic key, then an attacker may be able to easily guess the ID or cryptographic key and gain access to restricted functionality. | |
Potential Mitigations
Phase: Implementation Use functions or hardware which use a hardware-based random number generation for all crypto. This is the recommended solution. Use CyptGenRandom on Windows, or hw_rand() on Linux. |
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 |
---|
ChildOf | 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. | 330 | Use of Insufficiently Random Values |
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. 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003) Nature | Type | ID | Name |
---|
ChildOf | 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. | 330 | Use of Insufficiently Random Values |
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 |
---|
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 |
---|
Architecture and Design | | Implementation | REALIZATION: This weakness is caused during implementation of an architectural security tactic. |
Likelihood Of Exploit 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();
The random number functions used in these examples, rand() and Random.nextInt(), are not considered cryptographically strong. An attacker may be able to predict the random numbers generated by these functions. Note that these example also exhibit CWE-337 (Predictable Seed in PRNG). Observed Examples Reference | Description |
| PHP framework uses mt_rand() function (Marsenne Twister) when generating tokens |
| Crypto product uses rand() library function to generate a recovery key, making it easier to conduct brute force attacks. |
| Random number generator can repeatedly generate the same value. |
| Web application generates predictable session IDs, allowing session hijacking. |
| SSL library uses a weak random number generator that only generates 65,536 unique keys. |
Detection Methods
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 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 Base 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 | | | Non-cryptographic PRNG |
CERT C Secure Coding | MSC30-C | CWE More Abstract | Do not use the rand() function for generating pseudorandom numbers |
References
|
[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) | CLASP | | | Modifications |
---|
Modification Date | Modifier | Organization |
---|
2008-07-01 | Eric Dalci | Cigital | updated Time_of_Introduction | 2008-09-08 | CWE Content Team | MITRE | updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings | 2011-06-01 | CWE Content Team | MITRE | updated Common_Consequences | 2012-05-11 | CWE Content Team | MITRE | updated Common_Consequences, Observed_Examples, References, Relationships | 2012-10-30 | CWE Content Team | MITRE | updated Demonstrative_Examples, Potential_Mitigations | 2014-06-23 | CWE Content Team | MITRE | updated Applicable_Platforms, Description, Name, Other_Notes | 2015-12-07 | CWE Content Team | MITRE | updated Relationships | 2017-11-08 | CWE Content Team | MITRE | updated Demonstrative_Examples, Description, Modes_of_Introduction, Relationships, Taxonomy_Mappings | 2019-01-03 | CWE Content Team | MITRE | updated Relationships | 2020-02-24 | CWE Content Team | MITRE | updated References, Relationships | 2021-03-15 | CWE Content Team | MITRE | updated Demonstrative_Examples | 2021-07-20 | CWE Content Team | MITRE | updated Maintenance_Notes | 2021-10-28 | CWE Content Team | MITRE | updated Relationships | 2023-04-27 | CWE Content Team | MITRE | updated Detection_Factors, Relationships | 2023-06-29 | CWE Content Team | MITRE | updated Mapping_Notes | 2023-10-26 | CWE Content Team | MITRE | updated Observed_Examples | Previous Entry Names |
---|
Change Date | Previous Entry Name |
---|
2008-04-11 | Non-cryptographic PRNG | | 2014-06-23 | Use of Cryptographically Weak PRNG | |
More information is available — Please edit the custom filter or select a different filter.
|