The product does not properly filter, remove, quote, or otherwise manage the invalid use of special elements in user-controlled input, which could cause adverse effect on its behavior and integrity.

Primary

Implementation

Integrity
Unexpected State

Developers should anticipate that special elements will be injected/removed/manipulated in the input vectors of their software system. 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
Output Encoding
While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).

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.

CVE-2002-1362
Crash via message type without separator character
https://www.cve.org/CVERecord?id=CVE-2002-1362

CVE-2000-0116
Extra "<" in front of SCRIPT tag bypasses XSS prevention.
https://www.cve.org/CVERecord?id=CVE-2000-0116

Common Special Element Manipulations

SFP24
Tainted input to command

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

The list of children for this entry is far from complete. However, the types of special elements might be too precise for use within CWE.
Precise terminology for the underlying weaknesses does not exist. Therefore, these weaknesses use the terminology associated with the manipulation.
Customized languages and grammars, even those that are specific to a particular product, are potential sources of weaknesses that are related to special elements. However, most researchers concentrate on the most commonly used representations for data transmission, such as HTML and SQL. Any representation that is commonly used is likely to be a rich source of weaknesses; researchers are encouraged to investigate previously unexplored representations.

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, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2009-07-27
updated Potential_Mitigations

CWE Content Team
MITRE
2009-10-29
updated Maintenance_Notes, Other_Notes, Terminology_Notes

CWE Content Team
MITRE
2011-03-29
updated Description, Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
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
2014-06-23
updated Other_Notes

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-05-03
updated Potential_Mitigations

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms, Relationships

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

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2021-03-15
updated Maintenance_Notes

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Observed_Examples

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

Common Special Element Manipulations
Failure to Sanitize Special Element