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Home > CWE List > CWE-602: Client-Side Enforcement of Server-Side Security (4.18)
ID
CWE Glossary Definition

CWE-602: Client-Side Enforcement of Server-Side Security

Weakness ID: 602
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 is composed of a server that relies on the client to implement a mechanism that is intended to protect the server.
Extended Description
When the server relies on protection mechanisms placed on the client side, an attacker can modify the client-side behavior to bypass the protection mechanisms, resulting in potentially unexpected interactions between the client and server. The consequences will vary, depending on what the mechanisms are trying to protect.
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

Bypass Protection Mechanism; DoS: Crash, Exit, or Restart

Scope: Access Control, Availability

Client-side validation checks can be easily bypassed, allowing malformed or unexpected input to pass into the application, potentially as trusted data. This may lead to unexpected states, behaviors and possibly a resulting crash.

Bypass Protection Mechanism; Gain Privileges or Assume Identity

Scope: Access Control

Client-side checks for authentication can be easily bypassed, allowing clients to escalate their access levels and perform unintended actions.
Potential Mitigations
Phase(s) Mitigation

Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.

Architecture and Design
If some degree of trust is required between the two entities, then use integrity checking and strong authentication to ensure that the inputs are coming from a trusted source. Design the product so that this trust is managed in a centralized fashion, especially if there are complex or numerous communication channels, in order to reduce the risks that the implementer will mistakenly omit a check in a single code path.

Testing
Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Testing
Use tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session. These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.
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 Pillar Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things. 693 Protection Mechanism Failure
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. 565 Reliance on Cookies without Validation and Integrity Checking
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. 603 Use of Client-Side Authentication
PeerOf 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. 290 Authentication Bypass by Spoofing
PeerOf 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. 300 Channel Accessible by Non-Endpoint
PeerOf 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. 836 Use of Password Hash Instead of Password for Authentication
CanPrecede 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. 471 Modification of Assumed-Immutable Data (MAID)
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. 1012 Cross Cutting
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.
Architecture and Design Consider a product that consists of two or more processes or nodes that must interact closely, such as a client/server model. If the product uses protection schemes in the client in order to defend from attacks against the server, and the server does not use the same schemes, then an attacker could modify the client in a way that bypasses those schemes. This is a fundamental design flaw that is primary to many weaknesses.
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: ICS/OT (Undetermined Prevalence)

Class: Mobile (Undetermined Prevalence)

Likelihood Of Exploit
Medium
Demonstrative Examples

Example 1


This example contains client-side code that checks if the user authenticated successfully before sending a command. The server-side code performs the authentication in one step, and executes the command in a separate step.

CLIENT-SIDE (client.pl)

(good code)
Example Language: Perl
$server = "server.example.com";
$username = AskForUserName();
$password = AskForPassword();
$address = AskForAddress();
$sock = OpenSocket($server, 1234);
writeSocket($sock, "AUTH $username $password\n");
$resp = readSocket($sock);
if ($resp eq "success") {

# username/pass is valid, go ahead and update the info!
writeSocket($sock, "CHANGE-ADDRESS $username $address\n";
}
else {
print "ERROR: Invalid Authentication!\n";
}

SERVER-SIDE (server.pl):

(bad code)
Example Language: Perl
$sock = acceptSocket(1234);
($cmd, $args) = ParseClientRequest($sock);
if ($cmd eq "AUTH") {
($username, $pass) = split(/\s+/, $args, 2);
$result = AuthenticateUser($username, $pass);
writeSocket($sock, "$result\n");
# does not close the socket on failure; assumes the

# user will try again
}
elsif ($cmd eq "CHANGE-ADDRESS") {
if (validateAddress($args)) {
$res = UpdateDatabaseRecord($username, "address", $args);
writeSocket($sock, "SUCCESS\n");
}
else {
writeSocket($sock, "FAILURE -- address is malformed\n");
}
}

The server accepts 2 commands, "AUTH" which authenticates the user, and "CHANGE-ADDRESS" which updates the address field for the username. The client performs the authentication and only sends a CHANGE-ADDRESS for that user if the authentication succeeds. Because the client has already performed the authentication, the server assumes that the username in the CHANGE-ADDRESS is the same as the authenticated user. An attacker could modify the client by removing the code that sends the "AUTH" command and simply executing the CHANGE-ADDRESS.



Example 2


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.



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
SCADA system only uses client-side authentication, allowing adversaries to impersonate other users.
ASP program allows upload of .asp files by bypassing client-side checks.
steganography products embed password information in the carrier file, which can be extracted from a modified client.
steganography products embed password information in the carrier file, which can be extracted from a modified client.
client allows server to modify client's configuration and overwrite arbitrary files.
Weakness Ordinalities
Ordinality Description
Primary
(where the weakness exists independent of other weaknesses)
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. 722 OWASP Top Ten 2004 Category A1 - Unvalidated Input
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 753 2009 Top 25 - Porous Defenses
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. 975 SFP Secondary Cluster: Architecture
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1348 OWASP Top Ten 2021 Category A04:2021 - Insecure Design
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1413 Comprehensive Categorization: Protection Mechanism Failure
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
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
OWASP Top Ten 2004 A1 CWE More Specific Unvalidated Input
References
[REF-7] Michael Howard and David LeBlanc. "Writing Secure Code". Chapter 23, "Client-Side Security Is an Oxymoron" Page 687. 2nd Edition. Microsoft Press. 2002年12月04日.
<https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223>.
[REF-1283] Forescout Vedere Labs. "OT:ICEFALL: The legacy of "insecure by design" and its implications for certifications and risk management". 2022年06月20日.
<https://www.forescout.com/resources/ot-icefall-report/>.
Content History
Submissions
Submission Date Submitter Organization
2007年05月07日
(CWE Draft 6, 2007年05月07日) 		CWE Community
Submitted by members of the CWE community to extend early CWE versions
Modifications
Modification Date Modifier Organization
2025年04月03日
(CWE 4.17, 2025年04月03日) 		CWE Content Team MITRE
updated Demonstrative_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
2023年01月31日 CWE Content Team MITRE
updated Applicable_Platforms, Relationships, Type
2022年10月13日 CWE Content Team MITRE
updated Demonstrative_Examples, Description, Observed_Examples, References, Relationships
2022年04月28日 CWE Content Team MITRE
updated Research_Gaps
2021年10月28日 CWE Content Team MITRE
updated Relationships
2020年02月24日 CWE Content Team MITRE
updated Applicable_Platforms, Relationships
2019年06月20日 CWE Content Team MITRE
updated Related_Attack_Patterns
2018年03月27日 CWE Content Team MITRE
updated References
2017年11月08日 CWE Content Team MITRE
updated Applicable_Platforms, Enabling_Factors_for_Exploitation, Modes_of_Introduction, References, Relationships
2017年05月03日 CWE Content Team MITRE
updated Related_Attack_Patterns
2014年07月30日 CWE Content Team MITRE
updated Relationships
2012年05月11日 CWE Content Team MITRE
updated Relationships
2011年06月01日 CWE Content Team MITRE
updated Common_Consequences
2011年03月29日 CWE Content Team MITRE
updated Relationships
2010年12月13日 CWE Content Team MITRE
updated Related_Attack_Patterns
2010年04月05日 CWE Content Team MITRE
updated Related_Attack_Patterns
2010年02月16日 CWE Content Team MITRE
updated References
2009年10月29日 CWE Content Team MITRE
updated Applicable_Platforms, Common_Consequences, Description
2009年07月27日 CWE Content Team MITRE
updated Related_Attack_Patterns, Relationships
2009年05月27日 CWE Content Team MITRE
updated Demonstrative_Examples
2009年03月10日 CWE Content Team MITRE
updated Potential_Mitigations
2009年01月12日 CWE Content Team MITRE
updated Demonstrative_Examples, Description, Likelihood_of_Exploit, Name, Observed_Examples, Other_Notes, Potential_Mitigations, Relationships, Research_Gaps, Time_of_Introduction
2008年09月08日 CWE Content Team MITRE
updated Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008年07月01日 Eric Dalci Cigital
updated Time_of_Introduction
Previous Entry Names
Change Date Previous Entry Name
2008年04月11日 Client-Side Enforcement of Server-Side Security
2009年01月12日 Design Principle Violation: Client-Side Enforcement of Server-Side Security
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Page Last Updated: September 09, 2025

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