The product does not properly handle input in which an inconsistency exists between two or more special characters or reserved words.
An example of this problem would be if paired characters appear in the wrong order, or if the special characters are not properly nested.

Primary

Implementation

Availability
Access Control
Non-Repudiation
DoS: Crash, Exit, or Restart
Bypass Protection Mechanism
Hide Activities

Developers should anticipate that inconsistent special elements will be injected/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.

Implementation
Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Implementation
Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Inconsistent Special Elements

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.

PLOVER
2006-07-19
Draft 3
2006-07-19

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

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

CWE Content Team
MITRE
2008-10-14
updated Description

CWE Content Team
MITRE
2009-03-10
updated Relationships

CWE Content Team
MITRE
2009-07-27
updated Potential_Mitigations

CWE Content Team
MITRE
2010-12-13
updated Name

CWE Content Team
MITRE
2011-03-29
updated Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated 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 Potential_Mitigations

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms

CWE Content Team
MITRE
2020-02-24
updated Description, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2023-01-31
updated Description, Potential_Mitigations

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Relationships

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

Inconsistent Special Elements
Failure to Resolve Inconsistent Special Elements