Improper Neutralization of Whitespace

Description

This vulnerability occurs when an application fails to properly handle or sanitize whitespace characters in input before passing that data to another system component. This allows special whitespace elements to be interpreted incorrectly downstream, potentially altering how the data is processed.

Extended Description

Improper neutralization of whitespace happens when an application doesn't filter or escape characters like spaces, tabs, newlines, or non-breaking spaces before sending user-supplied input to a parser, database, or other subsystem. Attackers can exploit this by injecting these characters to manipulate file paths, alter command syntax, bypass input validation, or trigger unexpected behavior in the downstream component. Developers should implement strict input validation that defines and enforces allowed character sets, rejecting or sanitizing unwanted whitespace. To fix this, treat all user input as untrusted and use context-specific encoding or escaping—such as parameterized queries for databases or proper encoding for file system paths—before passing data to any internal or external component.

Common Consequences 1

Scope: Integrity

Impact: Unexpected State

Potential Mitigations 4

Developers should anticipate that whitespace will be injected/removed/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.

Phase: Implementation

Strategy: 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.

Phase: Implementation

Strategy: 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 (Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')).

Phase: Implementation

Strategy: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (Incorrect Behavior Order: Validate Before Canonicalize). Make sure that the application does not decode the same input twice (Double Decoding of the Same Data). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Observed Examples 3

CVE-2002-0637MIE. virus protection bypass with RFC violations involving extra whitespace, or missing whitespace.

CVE-2004-0942CPU consumption with MIME headers containing lines with many space characters, probably due to algorithmic complexity (RESOURCE.AMP.ALG).

CVE-2003-1015MIE. whitespace interpreted differently by mail clients.

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Alternate Terms

White space

Related Weaknesses

ChildOf:

Improper Neutralization of Special Elements (CWE-138)

Taxonomy Mapping

PLOVER
Software Fault Patterns

Notes

RelationshipCan overlap other separator characters or delimiters.