A client/server product performs authentication within client code but not in server code, allowing server-side authentication to be bypassed via a modified client that omits the authentication check.
Client-side authentication is extremely weak and may be breached easily. Any attacker may read the source code and reverse-engineer the authentication mechanism to access parts of the application which would otherwise be protected.

Primary

Architecture and Design
COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.

Implementation

Access Control
Bypass Protection Mechanism
Gain Privileges or Assume Identity

Architecture and Design
Do not rely on client side data. Always perform server side authentication.

In 2022, the OT:ICEFALL study examined products by 10 different Operational Technology (OT) vendors. The researchers reported 56 vulnerabilities and said that the products were "insecure by design" [REF-1283]. If exploited, these vulnerabilities often allowed adversaries to change how the products operated, ranging from denial of service to changing the code that the products executed. Since these products were often used in industries such as power, electrical, water, and others, there could even be safety implications.
Multiple vendors used client-side authentication in their OT products.

CVE-2022-33139
SCADA system only uses client-side authentication, allowing adversaries to impersonate other users.
https://www.cve.org/CVERecord?id=CVE-2022-33139

CVE-2006-0230
Client-side check for a password allows access to a server using crafted XML requests from a modified client.
https://www.cve.org/CVERecord?id=CVE-2006-0230

Allowed
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.
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.

Anonymous Tool Vendor (under NDA)
2007-05-07
Draft 6
2007-05-07

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Description, Relationships, Observed_Example, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Maintenance_Notes, Other_Notes

CWE Content Team
MITRE
2012-05-11
updated References, Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-05-03
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Modes_of_Introduction, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Maintenance_Notes, Relationships

CWE Content Team
MITRE
2022-10-13
updated Demonstrative_Examples, Observed_Examples, References, Relationships

CWE Content Team
MITRE
2023-01-31
updated Applicable_Platforms, Relationships

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes, Relationships

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Weakness_Ordinalities

Client-Side Authentication