Improper Neutralization of Multiple Internal Special Elements

Description

This vulnerability occurs when an application accepts external input but fails to properly sanitize multiple internal control characters or delimiters before passing that data to another internal component. This can cause the downstream component to misinterpret the data and execute unintended commands.

Extended Description

When an application processes complex data structures, it often uses internal special elements—like separators, escape sequences, or control characters—to parse information. If an attacker can inject multiple un-sanitized versions of these elements, they can manipulate the parsing logic. This forces the downstream component (like a data parser, interpreter, or internal API) to misinterpret boundaries and relationships within the data, leading to logic errors, data corruption, or injection attacks. To prevent this, developers must implement strict validation and encoding routines that neutralize all relevant internal special elements in the correct sequence and context. This is especially critical in data serialization/deserialization, configuration file processing, and when passing complex arguments between system modules. Security depends on treating all internal data streams as potentially tainted after they receive external input.

Common Consequences 1

Scope: Integrity

Impact: Unexpected State

Potential Mitigations 4

Developers should anticipate that multiple 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 Internal Special Elements (CWE-164)

Taxonomy Mapping

PLOVER
Software Fault Patterns