CWE - CWE-521: Weak Password Requirements (4.18)

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CWE Glossary Definition

CWE-521: Weak Password Requirements

Weakness ID: 521

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: 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.

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Description

The product does not require that users should have strong passwords, which makes it easier for attackers to compromise user accounts.

Extended Description

Authentication mechanisms often rely on a memorized secret (also known as a password) to provide an assertion of identity for a user of a system. It is therefore important that this password be of sufficient complexity and impractical for an adversary to guess. The specific requirements around how complex a password needs to be depends on the type of system being protected. Selecting the correct password requirements and enforcing them through implementation are critical to the overall success of the authentication mechanism.

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
Gain Privileges or Assume Identity	Scope: Access Control An attacker could easily guess user passwords and gain access user accounts.

Potential Mitigations

Phase(s)	Mitigation
Architecture and Design	A product's design should require adherance to an appropriate password policy. Specific password requirements depend strongly on contextual factors, but it is recommended to contain the following attributes: Enforcement of a minimum and maximum length Restrictions against password reuse Restrictions against using common passwords Restrictions against using contextual string in the password (e.g., user id, app name) Depending on the threat model, the password policy may include several additional attributes. Complex passwords requiring mixed character sets (alpha, numeric, special, mixed case) Increasing the range of characters makes the password harder to crack and may be appropriate for systems relying on single factor authentication. Unfortunately, a complex password may be difficult to memorize, encouraging a user to select a short password or to incorrectly manage the password (write it down). Another disadvantage of this approach is that it often does not result in a significant increases in overal password complexity due to people's predictable usage of various symbols. Large Minimum Length (encouraging passphrases instead of passwords) Increasing the number of characters makes the password harder to crack and may be appropriate for systems relying on single factor authentication. A disadvantage of this approach is that selecting a good passphrase is not easy and poor passwords can still be generated. Some prompting may be needed to encourage long un-predictable passwords. Randomly Chosen Secrets Generating a password for the user can help make sure that length and complexity requirements are met, and can result in secure passwords being used. A disadvantage of this approach is that the resulting password or passpharse may be too difficult to memorize, encouraging them to be written down. See NIST 800-63B [REF-1053] for further information on password requirements.
Architecture and Design	Consider a second authentication factor beyond the password, which prevents the password from being a single point of failure. See CWE-308 for further information.
Implementation	Consider implementing a password complexity meter to inform users when a chosen password meets the required attributes.
Implementation	Previously, "password expiration" was widely advocated as a defense-in-depth approach to minimize the risk of weak passwords, and it has become a common practice. Password expiration requires a password to be changed within a fixed time window (such as every 90 days). However, this approach has significant limitations in the current threat landscape, and its utility has been reduced in light of the adoption of related protection mechanisms (such as password complexity and computational effort), along with the recognition that regular password changes often caused users to generate more predictable passwords. As a result, this is now a Discouraged Common Practice [REF-1488] [REF-1489], especially as the sole factor in protecting passwords. It is still strongly encouraged to force password changes in case of evidence of compromise, but this is not the same as a forced "expiration" on an arbitrary time frame.

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.	1391	Use of Weak Credentials
ParentOf	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.	258	Empty Password in Configuration File

Relevant to the view "Software Development" (View-699)

Nature	Type	ID	Name
MemberOf	Category Category - a CWE entry that contains a set of other entries that share a common characteristic.	255	Credentials Management Errors

Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)

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.	287	Improper Authentication

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.	1010	Authenticate Actors

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	COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.
Implementation	Not enforcing the password policy stated in a products design can allow users to create passwords that do not provide the necessary level of protection.

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)

Technologies

Class: Not Technology-Specific (Undetermined Prevalence)

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
CVE-2020-4574	key server application does not require strong passwords

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.) Effectiveness: High

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.)

Effectiveness: High

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.	724	OWASP Top Ten 2004 Category A3 - Broken Authentication and Session Management
MemberOf	ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	884	CWE Cross-section
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	951	SFP Secondary Cluster: Insecure Authentication Policy
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1353	OWASP Top Ten 2021 Category A07:2021 - Identification and Authentication Failures
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1396	Comprehensive Categorization: Access Control

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 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.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
OWASP Top Ten 2004	A3	CWE More Specific	Broken Authentication and Session Management

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-112	Brute Force
CAPEC-16	Dictionary-based Password Attack
CAPEC-49	Password Brute Forcing
CAPEC-509	Kerberoasting
CAPEC-55	Rainbow Table Password Cracking
CAPEC-555	Remote Services with Stolen Credentials
CAPEC-561	Windows Admin Shares with Stolen Credentials
CAPEC-565	Password Spraying
CAPEC-70	Try Common or Default Usernames and Passwords

References

[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 19: Use of Weak Password-Based Systems." Page 279. McGraw-Hill. 2010.

[REF-1053] NIST. "Digital Identity Guidelines (SP 800-63B)". Sections: 5.1.1, 10.2.1, and Appendix A. 2017-06.
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-63b.pdf>. (URL validated: 2023年04月07日)

[REF-1488] NIST. "Digital Identity Guidelines (SP 800-63B-4)". 8.1.2.1. Passwords. 2025-07.
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-63B-4.pdf>. (URL validated: 2025年09月08日)

[REF-1489] National Cyber Security Centre. "Password Guidance: Simplifying Your Approach". Tip 2: Help users cope with password overload. 2015年09月14日.
<https://assets.publishing.service.gov.uk/media/5a806bb9e5274a2e87db9b6a/Password_guidance_-_simplifying_your_approach.pdf>. (URL validated: 2025年09月08日)

Content History

Submissions
Submission Date	Submitter	Organization
2006年07月19日 (CWE Draft 3, 2006年07月19日)	Anonymous Tool Vendor (under NDA)
2006年07月19日 (CWE Draft 3, 2006年07月19日)
Contributions
Contribution Date	Contributor	Organization
2025年03月17日 (CWE 4.18, 2025年09月09日)	Camille Gouttebroze	CAST Software
2025年03月17日 (CWE 4.18, 2025年09月09日)	suggested removal of password expiration as an acceptable mitigation and provided references
Modifications
Modification Date	Modifier	Organization
2025年09月09日 (CWE 4.18, 2025年09月09日)	CWE Content Team	MITRE
2025年09月09日 (CWE 4.18, 2025年09月09日)	updated Potential_Mitigations, References
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated Detection_Factors, Relationships
2022年10月13日	CWE Content Team	MITRE
2022年10月13日	updated Observed_Examples, Potential_Mitigations, Relationships
2021年10月28日	CWE Content Team	MITRE
2021年10月28日	updated Relationships
2020年08月20日	CWE Content Team	MITRE
2020年08月20日	updated Related_Attack_Patterns
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Applicable_Platforms, Description, Modes_of_Introduction, Potential_Mitigations, References
2019年06月20日	CWE Content Team	MITRE
2019年06月20日	updated Relationships
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Modes_of_Introduction, Relationships, Taxonomy_Mappings
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Common_Consequences, References, Relationships
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2011年03月29日	CWE Content Team	MITRE
2011年03月29日	updated Potential_Mitigations, Relationships
2009年05月27日	CWE Content Team	MITRE
2009年05月27日	updated Related_Attack_Patterns
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Description, Relationships, Taxonomy_Mappings
2008年08月15日	Veracode
2008年08月15日	Suggested OWASP Top Ten 2004 mapping
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Potential_Mitigations, Time_of_Introduction

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Page Last Updated: September 09, 2025

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