Improper Neutralization of Section Delimiters

Description

This vulnerability occurs when an application fails to properly sanitize or validate special characters that act as section delimiters in data streams. When this unsanitized input is passed to another component, these delimiters can be misinterpreted, leading to incorrect data parsing or unintended behavior.

Extended Description

During data parsing, unexpected delimiters—whether injected, missing, or malformed—can trick the system into processing information incorrectly. This often happens when boundaries between data sections aren't properly enforced, allowing attackers to manipulate structure and control flow. Common examples include multipart MIME message boundaries or double newline characters that signal section transitions. Without proper neutralization, these delimiters become injection points that can corrupt data interpretation, break parsing logic, or enable data smuggling between application layers.

Common Consequences 1

Scope: Integrity

Impact: Unexpected State

Potential Mitigations 4

Developers should anticipate that section delimiters 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.

References 1

The Art of Software Security Assessment

Mark Dowd, John McDonald, and Justin Schuh

Addison Wesley

2006

ID: REF-62

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Improper Neutralization of Delimiters (CWE-140)

CanAlsoBe:

Improper Neutralization of CRLF Sequences ('CRLF Injection') (CWE-93)

Taxonomy Mapping

PLOVER
Software Fault Patterns

Notes

RelationshipDepending on the language and syntax being used, this could be the same as the record delimiter (Improper Neutralization of Record Delimiters).