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Home > CWE List > CWE-340: Generation of Predictable Numbers or Identifiers (4.18)
ID
CWE Glossary Definition

CWE-340: Generation of Predictable Numbers or Identifiers

Weakness ID: 340
Vulnerability Mapping: ALLOWED This CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review (with careful review of mapping notes)
Abstraction: 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.
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Description
The product uses a scheme that generates numbers or identifiers that are more predictable than required.
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

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 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. 330 Use of Insufficiently Random Values
ParentOf 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. 341 Predictable from Observable State
ParentOf 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. 342 Predictable Exact Value from Previous Values
ParentOf 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. 343 Predictable Value Range from Previous Values
CanPrecede Composite Composite - a Compound Element that consists of two or more distinct weaknesses, in which all weaknesses must be present at the same time in order for a potential vulnerability to arise. Removing any of the weaknesses eliminates or sharply reduces the risk. One weakness, X, can be "broken down" into component weaknesses Y and Z. There can be cases in which one weakness might not be essential to a composite, but changes the nature of the composite when it becomes a vulnerability. 384 Session Fixation
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
Demonstrative Examples

Example 1


This code generates 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.

This example also exhibits a Small Seed Space (CWE-339).



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
Product for administering PBX systems uses predictable identifiers and timestamps for filenames (CWE-340) which allows attackers to access files via direct request (CWE-425).
PRNG allows attackers to use the output of small PRNG requests to determine the internal state information, which could be used by attackers to predict future pseudo-random numbers.
Listening TCP ports are sequentially allocated, allowing spoofing attacks.
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. 905 SFP Primary Cluster: Predictability
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. 1414 Comprehensive Categorization: Randomness
Vulnerability Mapping Notes
Usage ALLOWED-WITH-REVIEW
(this CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review)
Reason Abstraction

Rationale

This CWE entry is a Class and might have Base-level children that would be more appropriate

Comments

Examine children of this entry to see if there is a better fit
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 Predictability problems
WASC 11 Brute Force
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年07月19日
(CWE Draft 3, 2006年07月19日) 		PLOVER
Modifications
Modification Date Modifier Organization
2024年07月16日
(CWE 4.15, 2024年07月16日) 		CWE Content Team MITRE
updated Relationships
2024年02月29日
(CWE 4.14, 2024年02月29日) 		CWE Content Team MITRE
updated Demonstrative_Examples
2023年10月26日 CWE Content Team MITRE
updated Observed_Examples
2023年06月29日 CWE Content Team MITRE
updated Mapping_Notes
2023年04月27日 CWE Content Team MITRE
updated Relationships
2021年10月28日 CWE Content Team MITRE
updated Relationships
2021年07月20日 CWE Content Team MITRE
updated Maintenance_Notes
2020年02月24日 CWE Content Team MITRE
updated Description, Name, Relationships
2012年05月11日 CWE Content Team MITRE
updated References, Relationships
2011年06月27日 CWE Content Team MITRE
updated Common_Consequences
2011年06月01日 CWE Content Team MITRE
updated Common_Consequences
2010年02月16日 CWE Content Team MITRE
updated Taxonomy_Mappings
2008年09月08日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2008年07月01日 Eric Dalci Cigital
updated Time_of_Introduction
Previous Entry Names
Change Date Previous Entry Name
2020年02月24日 Predictability Problems
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Page Last Updated: September 09, 2025

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