CWE

Improper Handling of Additional Special Element

ID: 167		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: DRAFT
Abstraction Type: Base

Description

The software receives input from an upstream component, but it does not handle or incorrectly handles when an additional unexpected special element is missing.

Applicable Platforms
Language Class: All

Time Of Introduction

• Implementation

Common Consequences

Scope	Technical Impact	Notes
Integrity	Unexpected state

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
		Developers should anticipate that extra special elements will be injected in the input vectors of their software system. Use an appropriate combination of black lists and white lists 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 whitelist 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 (i.e., do not rely on a blacklist). A blacklist 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, blacklists 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 whitelist (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 whitelist validation schemes by introducing dangerous inputs after they have been checked.

Relationships

Related CWE	Type	View	Chain
CWE-167 ChildOf CWE-896	Category	CWE-888

Demonstrative Examples
None

Observed Examples

1. CVE-2000-0116 : Extra "<" in front of SCRIPT tag.
2. CVE-2001-1157 : Extra "<" in front of SCRIPT tag.
3. CVE-2002-2086 : "<script" - probably a cleansing error

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
PLOVER		Extra Special Element

References:
None