CWE

Improper Neutralization of Expression/Command Delimiters

ID: 146		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: INCOMPLETE
Abstraction Type: Variant

Description

The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as expression or command delimiters when they are sent to a downstream component.

Extended Description

As data is parsed, an injected/absent/malformed delimiter may cause the process to take unexpected actions.

Applicable Platforms
Language Class: Language-independent

Time Of Introduction

• Implementation

Related Attack Patterns

• CAPEC-15
• CAPEC-6

Common Consequences

Scope	Technical Impact	Notes
Confidentiality Integrity Availability Other	Execute unauthorized code or commands Alter execution logic

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
		Developers should anticipate that inter-expression and inter-command delimiters will be injected/removed/manipulated in the input vectors of their software 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
A shell metacharacter (covered in CWE-150) is one example of a potential delimiter that may need to be neutralized.

Related CWE	Type	View	Chain
CWE-146 ChildOf CWE-896	Category	CWE-888

Demonstrative Examples
None

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
PLOVER		Delimiter between Expressions or Commands

References:

1. Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 8, "Embedded Delimiters", Page 408.'. Published on 2006.