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Improper Neutralization of Delimiters

Draft Base
Structure: Simple
Description

This vulnerability occurs when an application fails to properly handle or sanitize delimiter characters within data inputs, allowing them to be misinterpreted by downstream systems.

Extended Description

Delimiters, like commas, quotes, or newlines, are special characters used to structure data. When an application doesn't neutralize these characters in user-controlled input, an attacker can inject their own delimiters. This can corrupt data files, break parsing logic, or enable injection attacks by tricking the system into misreading the boundaries of a data field. To prevent this, developers must treat all user input as untrusted. Implement strict input validation using allowlists for expected characters and encode or escape delimiters based on the specific context where the data will be used, such as in CSV files, command lines, or configuration data. Relying on blacklists is error-prone, as it's easy to miss obscure or alternative delimiter encodings.
Common Consequences 1
Scope: Integrity

Impact: Unexpected State
Potential Mitigations 4
Phase: Implementation

Strategy: Input Validation

Developers should anticipate that 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.
Observed Examples 4
CVE-2003-0307Attacker inserts field separator into input to specify admin privileges.
CVE-2000-0293Multiple internal space, insufficient quoting - program does not use proper delimiter between values.
CVE-2001-0527Attacker inserts carriage returns and "|" field separator characters to add new user/privileges.
CVE-2002-0267Linebreak in field of PHP script allows admin privileges when written to data file.
Modes of Introduction
Implementation
Related Attack Patterns
Related Weaknesses
ChildOf: Improper Neutralization of Special Elements (CWE-138)
Taxonomy Mapping
  • PLOVER
  • Software Fault Patterns