Improper Neutralization of Internal Special Elements

Description

This vulnerability occurs when an application accepts data from a source but fails to properly sanitize internal control elements or metadata before passing it to another internal component. This can cause the downstream component to misinterpret the data and perform unintended actions.

Extended Description

Think of this as a breakdown in communication between two trusted parts of your own system. When one module sends data containing special instructions or formatting (like internal delimiters, escape sequences, or length indicators) to another, the receiving component might process those elements as commands instead of inert data. This internal confusion can corrupt data flows, trigger logic errors, or bypass security checks, leading to crashes or unauthorized behavior. For developers, the core issue is assuming data from an upstream component (even within the same application) is already safe or correctly formatted. The fix requires implementing strict validation and neutralization at the trust boundary between these components. Always treat internal data streams with the same suspicion as external input, ensuring special elements are escaped, removed, or handled in a way that prevents misinterpretation.

Common Consequences 1

Scope: Integrity

Impact: Unexpected State

Potential Mitigations 4

Developers should anticipate that internal special elements 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.

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Improper Neutralization of Special Elements (CWE-138)

Taxonomy Mapping

PLOVER
Software Fault Patterns